FULL PAPER DOI: 10.1002/asia.201402627
Mechanochromic Luminescence of Fluorenyl-Substituted Ethylenes Yun Lv, Yang Liu,* Dan Guo, Xin Ye, Guangfeng Liu, and Xutang Tao*[a] Abstract: It has been reported several times that some organic luminogens with aggregation-induced emission (AIE) characteristics exhibit the abnormal phenomenon of crystallization-induced blueshift fluorescence, which makes them suitable for utilization as luminescence color-switching materials. Because of the attractive application potential and the numerous underlying structure–property relationships in such materials, we investigated a series
of fluorenyl-containing tetrasubstituted ethylenes for their novel optical properties and structural features. The dyes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solKeywords: aggregation · ethylenes · luminescence · morphology · substituent effects
Introduction
shows distinct fluorescence in different polymorphs, for example, in the amorphous and crystalline state. The mechano-stimuli that can induce certain crystalline materials into the amorphous state can trigger ML. In this field a longterm goal is to develop candidates with large contrast and strong emissions. Given that many common luminogens severely decrease their luminescence in the condensed phase, thereby making them unfit for the use in efficient and highcontrast ML, aggregation-induced emission (AIE) luminogens with strong emissions in the solid state are superior candidates. Since the discovery of the piezofluorochromic phenomenon based on an AIE compound in 2010,[8] a number of AIE compounds with reversible ML have been successfully prepared by other groups.[9] The fluorescence of many such materials depends on their morphology, which shows abnormal crystallization-induced blueshift emission.[10] Researchers have checked the structures and packing motifs of the AIE materials to find correlations between structures and the AIE property.[6, 7] For the AIE materials with ML ability, the structural relationship has also been recognized on the basis of recent experimental results.[9, 11] To achieve the molecular design of promising ML materials, the structural features of the smart compounds should be thoroughly investigated along with the underlying mechanism as to why the materials change their intermolecular interactions or intramolecular conformations in response to mechanical stimuli, and how this change causes fluorescence shift should be fully understood. Here we have investigated the ML property of a series of fluorenyl-containing tetrasubstituted ethylenes. By analyzing their single-crystal XRD structures and optical and thermal properties, we discussed the effect of different substituents and the molecular arrangements on the ML behavior, as well as the solventfuming crystallization process.
Mechanochromic luminescence (ML) materials have attracted a great deal of interest because of their potential applications in sensors, security materials, and information display and storage.[1] Normally, ML materials produce clear fluorescence intensity and/or color changes as a result of the transformation of chemical or physical structures in which the transformation is sensitive to external stimuli such as mechanical forces, solvent fuming, or thermal treatment.[2–5] For example, the tuning of the emission of some organic materials was implemented through changing the chemical structures that involved the opened/closed cyclic form[2] or double-bond E/Z isomerization.[3] However, some reports focused on controlling the mode of molecular packing by means of the crystalline-to-amorphous transition[4] or the phase shift of the liquid-crystalline state.[5] Recently, researchers have begun to pay more and more attention to changing the intermolecular interactions of chromophores by means of mechano-stimuli, which is believed to be more facile when achieving highly efficient and reversible ML.[6] Up to now most research efforts have proved that the emission property of some organic solids has a close relationship with the regularity of molecular packing.[7] Researchers have encountered many cases in which the same compound [a] Y. Lv, Prof. Dr. Y. Liu, D. Guo, X. Ye, G. Liu, Prof. Dr. X. Tao State Key Laboratory of Crystal Materials Key Laboratory of Functional Crystal Materials and Devices of MOE, Shandong University Jinan, Shandong 250100 (P.R. China) E-mail: [email protected] [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201402627.
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
vent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing. Through single-crystal and X-ray diffraction (XRD) analysis, the twisted molecular geometries and loose packing motifs in the crystalline samples are believed to be the intrinsic origin of the external-stimuli-induced structural transformation.
1
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
Results and Discussion
The three dyes are readily soluble in common organic solvents such as CH2Cl2, chloroform, and THF, but not in water. They are typical AIE luminogens such as tetraphenACHTUNGREylACHTUNGREethene (TPE), which have nearly no emission in solutions but strong emission in the aggregation states. The Supporting Information shows the fluorescence change of the three samples from solution to aggregates in aqueous suspensions. The photoluminescence (PL) spectra of BBFT, BFT1, and BFT2 in THF are basically flat lines parallel to the abscissa, which reveals that they are genuinely weak emitters in the solution state. In pure THF, the quantum yields of all the three compounds are lower than 1 %. When a large amount of water is added into their solutions in THF, intense PL signals are recorded under identical measurement conditions at 515, 510, and 518 nm, respectively. After the water fraction (Wf) in the H2O/THF mixtures is larger than approximately 60 %, the dissolved molecular species start to aggregate; this is accompanied by rapid photoluminescence boosting. As shown in the Supporting Information, from the molecular solution in THF to the aggregate suspension in 95 % aqueous mixture, the PL intensities of all the three luminogens enhance more than one hundred times. In the Wf = 95 % aqueous mixtures, their fluorescence quantum yields reached 65, 58, and 60 %, respectively. The inset images in Figures S4 and S5 in the Supporting Information demonstrate the nonluminescent and emissive natures of the molecular isolated species and aggregates.[13] BBFT, BFT1, and BFT2 exhibit bright emission in the solid state. As shown in Figure 1, when excited at 365 nm, the luminogens in the crystalline and powder state display distinct fluorescence color, thus indicating a morphology-dependent luminescence. The PL spectra of the samples are shown in Figure 2. The crystals of BBFT, BFT1, and BFT2 show intense blue luminescence at 459 to 470 nm; and the as-prepared powders show greenish-yellow emission at 507 to 517 nm. The fluorescent quantum yields of the compounds in different solid states were measured by an absolute method using an integrating sphere whereby the respective yield in crystalline form is superior to that of the powder, with the data ranging from 56 to 88 %. The powder X-ray diffraction (PXRD) analysis confirmed the amorphous state of the as-prepared powders, which means the luminogens show an abnormal phenomenon of crystallizationinduced blueshift fluorescence. This stands in contrast to the well-known idea that for most common chromophores crystallization leads to emission quenching and redshift owing to strong intermolecular interactions and multiple excited-state decay pathways formed in crystals.[14, 15] According to previous studies, the fluorescence of such AIE solids can be affected by external stimuli.[6, 9, 11] We thus checked the ML behavior of the three compounds. As depicted in Figure 2, when we ground the crystalline samples of BBFT, BFT1, and BFT2 with a pestle or sheared them with a spatula, their fluorescence switched simultaneously during the process of grinding, and ultimately the entire blue-emissive samples turned into greenish ones. Figure 2 presents the PL spectra of the initial crystals and the ground powders, in
The chemical structures of the three tetrasubstituted ethylenes—1,2-bis(7-bromo-9,9-dibutylfluorenyl)-1,2-diphenylACHTUNGREethene (BBFT), 1,2-bis(9,9-dibutylfluorenyl)-1,2-diphenylACHTUNGREethene (BFT1), and 1,2-bis(2-fluorenyl-7-bromo)-1,2-diphenylethene (BFT2)—are shown in Figure 1. BBFT contains two bromo-substituted 9,9-dibutylfluorenyl units. The alkyl chains were introduced to facilitate its ability to self-assemble; and likewise the bromo atoms were incorporated to introduce more intermolecular interactions. For comparisons, BFT1, which contained only alkyl chains, and BFT2, which contained only bromo substituents, were prepared. The three compounds were all synthesized through the typical reactions of Zn/TiCl4-mediated McMurry coupling.[12] The products were purified by using silica gel column chromatography with dichloromethane/petroleum ether as the eluent and was then precipitated by pouring their solutions in CH2Cl2 into ethanol to yield the as-prepared powders. The crystals of BBFT, BFT1, and BFT2 were obtained by slow evaporation of a solution of ethanol/CH2Cl2 at room temperature. The identity and purity of the new compounds were verified by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis.
Figure 1. Chemical structures of BBFT, BFT1, and BFT2, and the corresponding fluorescent images of crystalline and as-prepared powders. Sacle bars, 100 mm.
Abstract in Chinese:
&
&
Chem. Asian J. 2014, 00, 0 – 0
Yang Liu, Xutang Tao et al.
2
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
www.chemasianj.org
Yang Liu, Xutang Tao et al.
color before and after grinding demonstrates high contrast: for BBFT, the PL redshifted about 58 nm to 517 nm from 459 nm of the crystals; for BFT1 and BFT2, the fluorescence redshifted from 473 to 507 nm, and from 464 to 516 nm, respectively. From the degree of emission shift in the ML process, we found that the incorporation of bromo substituents on the one hand makes the emission in crystals more blue and, on the other hand, redshifts the emission in the amorphous state. The fluorescence shifts of the bromo-containing compounds BBFT and BFT2 (58 and 52 nm) are clearly larger than that of BFT1 (34 nm) without bromo substituents, which is in Figure 2. Fluorescence images of a) BBFT, b) BFT1, and c) BFT2 in the grinding process and the correspondfavor of a high-contrast ML. ing fluorescence spectra of the dyes in d) crystalline, e) as-prepared powders, and f) ground powders. Like many other chromophores with ML properties, the fluorescence transition of these fluorenyl-containing ethylwhich we can see that the spectral profiles of the ground enes can be reversed by fuming under a solvent atmosphere. powders almost coincide with those of the as-prepared powAs shown in Figure 3, for the compounds BBFT and BFT1 ders, thus indicating their amorphous state. The emission with alkyl chains, the emission color of ground powders can be reversed by ethanol vapor fuming. After fumigation, their emission peaks blueshifted 51 and 35 nm, thereby resembling that of the respective initial crystals, whereas for compound BFT2 without alkyl chains, fuming by ethanol vapor could not restore the emission color, probably on account of its poor crystallization capacity. After many trials we found that the blue luminescence of the ground powder of BFT2 could be reversed by fuming it with CH2Cl2. By means of such a process of grinding and solvent fuming, the fluorescence of the three dyes could be transformed repeatedly. This fluorescence reversion is believed to be the result of an amorphous-to-crystalline transition, which is confirmed by the XRD patterns of different forms, as shown in Figure 4. We can see that both crystals and the fumed powders have sharp diffraction peaks, whereas for the ground powders, their diffraction patterns are nearly flat lines with inconspicuous broad peaks. This reveals that the crystallinity was significantly reduced through grinding to crush the structured molecular packing into disorder in the ground powders. The diffraction peaks of the fumed powders coincide with those of the initial crystals, thus implying that after being fumigated with organic solvent the molecules go back into packing in a crystalline form similar to that in crystals. Thus the morphological nature of these dyes can be distinguished by the luminance color: blue corresponds to crystalline and green corresponds to amorphous. Figure 3. PL spectra of the ground and fumed powder of a) BBFT, The effect of the solvent during fumigation is believed to b) BFT1, and c) BFT2. Inset: Photographs of ground (left) and fumed increase the molecular activity and facilitate the rearrange(right) samples under UV illumination.
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
3
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
Yang Liu, Xutang Tao et al.
and ethanol are very poor solvents, but CH2Cl2 and chloroform are good ones. However, the solvent-fuming behavior of BFT2 is different to that of BBFT and BFT1. For BFT2, CH2Cl2 and chloroform can promote the transformation from the amorphous to crystalline state, whereas ethanol cannot. We propose that whether or not a solvent vapor induFigure 4. XRD spectra of a) BBFT, b) BFT1, and c) BFT2 in different forms (crystals, ground powder, and ces crystallization or amorphifumed powder). zation is actually determined by the crystallizing ability and the crystallization habit of the specific solute in this solvent. ment of molecules from being random to ordered. With BBFT and BFT1 have four n-butyl chains, which can faciliregard to the solvent-fuming-assisted recrystallization, some tate the self-assembly activity of the molecules. Therefore, reports have proposed that all good solvents can play such under an ethanol atmosphere their molecules can be reara role in inducing crystallization.[15] However, from our exranged, whereas the significant dissolving capacity of perimental results, this might not be exact. We found that by CH2Cl2 would disturb the ordered molecular arrangement. using solvents such as methanol and ethanol as the fuming For the rigid BFT2 molecules, however, ethanol is unable to agent, the fluorescence recovery from green to blue can be promote orderly molecular movement. The activity of the realized for the amorphous powders of BBFT and BFT1. molecular arrangement is also influenced by the fuming Other solvents such as CH2Cl2 and chloroform have no such temperature. As shown in Figure S6 in the Supporting Inforeffect. Conversely, fuming with them could cause the crystalmation, the reversion speed of BBFT can be tuned by the line materials of BBFT and BFT1 to become amorphous, acfumigation temperature of the ethanol atmosphere. When companied by a fluorescence change from blue to green. As the temperature of the fuming system was elevated from 20 shown in Figure 6b, reversible fluorescence changing can be to 80 8C, the fluorescence reversion time was reduced from achieved on the BBFT film by alternately repeating ethanol and CH2Cl2 solvent fuming. In fact, for these dyes, methanol 2 h to 3 min. The higher temperature increases both the
Figure 5. a) Molecular conformation of BBFT in the crystal defined by X-ray crystallography. b) The crystal packing of the BBFT molecule. c) The C H···Br interaction (I) and d) C H···p interaction (II). The vertical distance between H and Br (I), H and the p-ring centroid (II), and the parallel neighboring fluorenyl rings are also marked.
&
&
Chem. Asian J. 2014, 00, 0 – 0
4
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
www.chemasianj.org
cious voids. Such kinds of crystal have low lattice energy, which allows them to be easily destroyed by external pressure.[5, 6] Once the lattice bindings collapse, the twisted molecular conformation constrained by the crystalline lattice can relax to a more planarized conformation, thereby generating redshifted emissions. Theoretical optimization on BBFT by using density functional theory calculations proves a more planar molecular geometry in the free isolated state than that in the X-ray crystal structure. The crystal structures of BFT1 and BFT2 are presented in the Supporting Information, which also shows the twisted structures and loose packing. In BFT1, there is only one kind of C H···p intermolecular interaction with a distance of 2.95 ; and in BFT2, only an intermolecular C H···p interaction with a distance of 2.74 formed. In a word, in this series of materials, the severe twisted molecular conformation induces a noncompact molecular packing that is easy to subject to the phase transition from crystalline to amorphous initiated by mechanical pressure. During the transition process, the planarization of the twisted molecules results in the pronounced luminescence color change, which is the origin of the ML.[6, 7] Given the ML property, we investigated their use as pressure-sensitive papers. As shown in Figure 6a, a piece of filter paper spray-coated with crystalline BBFT emits bright blue light under UV light; when inscribing the letters SDU on it with a spatula, the letters emit intense greenish light, which can be distinguished easily from the blue background. The letters can be erased upon ethanol solvent fumigation. This result demonstrates that the materials can potentially be applicable in optical recording, security inks, and latent image developers. Additionally, by making use of the reversible change in morphology induced by different solvent vapors, these materials might also be used as sensors to distinguish specific solvents (Figure 6b).
Figure 6. a) Procedures of using a crystalline BBFT film as pressure-sensitive paper: writing with a spatula and erasing by fuming with ethanol vapor. b) The different responses of BBFT film to the CH2Cl2 and ethanol vapor. Photos were taken under 365 nm UV light.
vapor pressure and the activity of molecules, thus making the speed of the phase transition faster. Up to now, the ML behavior in a number of AIE materials has been proven to result from the morphological change between crystalline and amorphous states.[6] However, it is known that it is unlikely for most other crystalline materials to be manually ground into the amorphous state, because the energy needed to destroy a crystal unit cell is immense. To learn why amorphization occurs easily in these materials, and to gain a deeper understanding of the ML mechanism, we analyzed their crystal structures. Figure 5 shows the crystal structure and packing motif of BBFT, in which the molecules adopt a highly twisted conformation. The dihedral angles between each of the two substituents of the alkene are quite large. For instance, the dihedral angles between the two fluorenyl (1 and 2) and the two phenyl (3 and 4) planes are 84.1 and 58.98, respectively. The large torsion shortens the effective conjugation length of the molecule and hence causes it to emit shorter-wavelength light in crystals. However, such a geometry hampers the close intermolecular p–p stacking and causes the molecules to adopt a loose packing in the condensed state. Therefore another characteristic of the crystal packing is the absence of strong intermolecular interactions. In addition to van der Waals forces, the molecules assemble through two primary weak intermolecular interactions that contain C H···Br (Figure 5c) and C H···p interactions (Figure 5d). Each bromo substituent is in contact with an alkyl hydrogen of another molecule to form a C H···Br interaction with an H···Br bond length of 2.82 . The C H···p interactions are formed between an aromatic hydrogen of a fluorenyl unit and another fluorenyl ring that belongs to a neighboring molecule, with a distance between H and the p-ring centroid of 2.73 . Figure 5b depicts the packing motif of BBFT, in which the molecules are packed in an ABAB (two different molecular orientations) periodic arrangement. The nearest vertical distance between two neighboring overlapped fluorenyl rings with a sliding angle of 22.778 is approximately 7.96 , which is too large to shape any p–p interactions. Thus the absence of strong intermolecular interactions leads to a loose packing motif and the appearance of many capa-
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
Yang Liu, Xutang Tao et al.
Conclusion In this report we developed a series of AIE-active fluorenylcontaining tetrasubstituted ethylenes with the aim of creating efficient and high-contrast mechanochromic luminescence materials. The luminogens show morphology-dependent fluorescence color: deep blue in crystals and green in the amorphous state. By means of mechanical grinding and solvent fuming, their morphologies transform between amorphous and crystalline, thereby resulting in emission switching between green and blue. Different substituents proved to have a clear effect on the optical and ML behaviors. By analysis of their XRD crystal structures and arrangements, the twisted molecular conformations, weak intermolecular interactions, and loose packing were found to be the common features in their structures and are responsible for the occurrence of the mechanochromic luminescence. We believe that this study will not only enrich the family of ML materials but also provide a deep understanding of the tuning of solid-state luminescent properties.
5
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
[6] a) Z. Chi, X. Zhang, B. Xu, J. R. Xu, Chem. Soc. Rev. 2012, 41, 3878 – 3896; b) D. R. T. Roberts, S. J. Holder, J. Mater. Chem. 2011, 21, 8256 – 8268; c) S. Perruchas, X. F. L. Goff, S. Maron, I. Maurin, F. Guillen, A. Garcia, T. Gacoin, J. Boilot, J. Am. Chem. Soc. 2010, 132, 10967 – 10969; d) Z. Yang, Z. Chi, T. Yu, X. Zhang, M. Chen, B. Xu, S. Liu, Y. Zhang, J. R. Xu, J. Mater. Chem. 2009, 19, 5541 – 5546; e) H. Ito, T. Saito, N. Oshima, N. Kitamura, S. Ishizaka, Y. Hinatsu, M. Wakeshima, M. Kato, K. Tsuge, M. Sawamura, J. Am. Chem. Soc. 2008, 130, 10044 – 10045; f) T. Lasanta, M. E. Olmos, A. Laguna, J. M. Lpez-de-Luzuriaga, P. Naumov, J. Am. Chem. Soc. 2011, 133, 16358 – 16361. [7] a) G. Li, F. Song, D. Wu, J. Lan, X. Liu, J. Wu, S. Yang, D. Xiao, J. You, Adv. Funct. Mater. 2014, 24, 747 – 753; b) A. Fukazawa, D. Kishi, Y. Tanaka, S. Seki, S. Yamaguchi, Angew. Chem. Int. Ed. 2013, 52, 12091 – 12095; Angew. Chem. 2013, 125, 12313 – 12317; c) T. Han, Y. Zhang, X. Feng, Z. Lin, B. Tong, J. Shi, J. Zhi, Y. Dong, Chem. Commun. 2013, 49, 7049 – 7051; d) B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629 – 1658; e) P. J. Diemer, C. R. Lyle, Y. Mei, C. Sutton, M. M. Payne, J. E. Anthony, V. Coropceanu, J.-L. Brdas, O. D. Jurchescu, Adv. Mater. 2013, 25, 6956 – 6962. [8] S. J. Yoon, J. W. Chung, J. Gierschner, K. S. Kim, M. G. Choi, D. Kim, S. Y. Park, J. Am. Chem. Soc. 2010, 132, 13675 – 13683. [9] a) B. Xu, Z. Chi, J. Zhang, X. Zhang, H. Li, X. Li, S. Liu, Y. Zhang, J. R. Xu, Chem. Asian J. 2011, 6, 1470 – 1478; b) X. Luo, J. Li, C. Li, L. Heng, Y. Q. Dong, Z. Liu, Z. Bo, B. Z. Tang, Adv. Mater. 2011, 23, 3261 – 3265; c) X. Luo, W. Zhao, J. Shi, C. Li, Z. Liu, Z. Bo, Y. Q. Dong, B. Z. Tang, J. Phys. Chem. C 2012, 116, 21967 – 21972. [10] W. Yuan, Y. Tan, Y. Gong, P. Lu, J. W. Y. Lam, X. Shen, C. Feng, H. H-Y. Sung, Y. Lu, I. D. Williams, J. Sun, B. Z. Tang, Adv. Mater. 2013, 25, 2837 – 2843. [11] X. Y. Shen, Y. J. Wang, E. Zhao, W. Z. Yuan, Y. Liu, P. Lu, A. Qin, Y. Ma, J. Z. Sun, B. Z. Tang, J. Phys. Chem. C 2013, 117, 7334 – 7347. [12] a) Y. Liu, Y. Lv, X. T. Tao, B. Z. Tang, Chem. Asian J. 2012, 7, 2424 – 2428; b) Y. Liu, X. H. Chen, Y. Lv, X. T. Tao, B. Z. Tang, Chem. Eur. J. 2012, 18, 9929 – 9938; c) Y. Liu, Y. Lv, H. Xi, X. Zhang, S. Chen, J. W. Y. Lam, R. T. K. Kwok, F. Mahtab, H. S. Kwok, X. Tao, B. Z. Tang, Chem. Commun. 2013, 49, 7216 – 7218; d) Y. Liu, X. Ye, G. Liu, Y. Lv, X. Zhang, S. Chen, J. W. Y. Lam, H. S. Kwok, X. Tao, B. Z. Tang, J. Mater. Chem. C 2014, 2, 1004 – 1009. [13] a) Y. Liu, S. Chen, J. W. Y. Lam, F. Mahtab, H. S. Kwok, B. Z. Tang, J. Mater. Chem. 2012, 22, 5184 – 5189; b) X. Zhang, Z. Chi, H. Li, B. Xu, X. Li, S. Liu, Y. Zhang, J. Xu, J. Mater. Chem. 2011, 21, 1788 – 1796. [14] a) Y. Liu, X. Tao, F. Wang, X. Dang, D. Zou, Y. Ren, M. Jiang, Org. Electron. 2009, 10, 1082; b) Review: M. Shimizu, T. Hiyama, Chem. Asian J. 2010, 5, 1516 – 1531; c) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332 – 4353; d) M. S. Kwon, J. Gierschner, S. Yoon, S. Y. Park, Adv. Mater. 2012, 24, 5487 – 5492. [15] a) N. Mizoshita, T. Tani, S. Inagaki, Adv. Mater. 2012, 24, 3350 – 3355; b) X. Zhang, Z. Chi, H. Li, B. Xu, X. Li, W. Zhou, S. Liu, Y. Zhang, J. R. Xu, Chem. Asian J. 2011, 6, 808 – 811.
Experimental Section The three compounds were synthesized through the typical reactions of AlCl3-catalyzed Friedel–Crafts acylation and Zn/TiCl4-mediated McMurry coupling.[12] Details of the synthetic procedures and characterization data are presented in the Supporting Information. Crystal structure analysis was carried out with a Bruker SMART APEX-II equipped with a CCD area-detector diffractometer at 296(2) K using graphite-monochromated MoKa radiation (l = 0.71073 ) with the w scan method. The structures were solved by direct methods and refined by the full-matrix least-squares technique on F2 using SHELX programs. CCDC-909142 (BBFT), 974227 (BFT1), and 974229 (BFT2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements We thank the National Natural Science Foundation of China (grant nos. 51021062, 51303095, 50990061, 51003054, and 51272129), the Promotive Research Fund for Young Scientists of Shandong Province (BS2012L020), and the 973 Program of the Peoples Republic of China (grant no. 2010CB630702) for financial support.
[1] a) G. Zhang, J. Lu, M. Sabat, C. L. Fraser, J. Am. Chem. Soc. 2010, 132, 2160 – 2162; b) A. Pucci, F. D. Cuia, F. Signori, G. Ruggeri, J. Mater. Chem. 2007, 17, 783 – 790; c) Z. Ning, Z. Chen, Q. Zhang, Y. Yan, S. Qian, Y. Cao, H. Tian, Adv. Funct. Mater. 2007, 17, 3799 – 3807; d) A. Kishimura, T. Yamashita, K. Yamaguchi, T. Aida, Nat. Mater. 2005, 4, 546 – 549; e) S. Hirata, T. Watanabe, Adv. Mater. 2006, 18, 2725 – 2729; f) C. E. Olson, M. J. R. Previte, J. T. Fourkas, Nat. Mater. 2002, 1, 225 – 228; g) S. M. Jeong, S. Song, S. Lee, N. Y. Ha, Adv. Mater. 2013, 25, 6194 – 6200; h) Z. Zhang, B. Xu, J. Su, L. Shen, Y. Xie, H. Tian, Angew. Chem. Int. Ed. 2011, 50, 11654 – 11657; Angew. Chem. 2011, 123, 11858 – 11861. [2] a) D. A. Davis, A. Hamilton, J. Yang, L. D. Cremar, D. V. Gough, S. L. Potisek, M. T. Ong, P. V. Braun, T. J. Martnez, S. R. White, J. S. Moore, N. R. Sottos, Nature 2009, 459, 68 – 72; b) C. K. Lee, D. A. Davis, S. R. White, J. S. Moore, N. R. Sottos, P. V. Braun, J. Am. Chem. Soc. 2010, 132, 16107 – 16111. [3] A. Schçnberg, M. Elkaschef, M. Nosseir, M. M. Sidky, J. Am. Chem. Soc. 1958, 80, 6312 – 6315. [4] a) J. Wang, J. Mei, R. Hu, J. Z. Sun, A. Qin, B. Z. Tang, J. Am. Chem. Soc. 2012, 134, 9956 – 9966; b) B. Xu, Z. Chi, J. Zhang, X. Zhang, H. Li, S. Liu, Y. Zhang, J. R. Xu, Chem. Commun. 2011, 47, 11080 – 11082; c) X. Gu, J. Yao, G. Zhang, Y. Yan, D. Zhang, Adv. Funct. Mater. 2012, 22, 4862 – 4872; d) X. Zhang, Z. Chi, J. Zhang, H. Li, B. Xu, X. Li, S. Liu, Y. Zhang, J. R. Xu, J Phys Chem. B 2011, 115, 7606 – 7611. [5] a) Y. Sagara, T. Kato, Angew. Chem. Int. Ed. 2008, 47, 5175 – 5178; Angew. Chem. 2008, 120, 5253 – 5256; b) Y. Sagara, T. Kato, Angew. Chem. Int. Ed. 2011, 50, 9128 – 9132; Angew. Chem. 2011, 123, 9294 – 9298.
&
&
Chem. Asian J. 2014, 00, 0 – 0
Yang Liu, Xutang Tao et al.
Received: June 8, 2014 Published online: && &&, 0000
6
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
FULL PAPER A glowing report: A series of fluorenyl-containing tetrasubstituted ethylenes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solvent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing (see figure).
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
Luminescence Yun Lv, Yang Liu,* Dan Guo, Xin Ye, Guangfeng Liu, &&&&—&&&& Xutang Tao* Mechanochromic Luminescence of Fluorenyl-Substituted Ethylenes
7
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
Mechanochromic Luminescence of Fluorenyl-Substituted Ethylenes Yun Lv, Yang Liu,* Dan Guo, Xin Ye, Guangfeng Liu, and Xutang Tao*[a] Abstract: It has been reported several times that some organic luminogens with aggregation-induced emission (AIE) characteristics exhibit the abnormal phenomenon of crystallization-induced blueshift fluorescence, which makes them suitable for utilization as luminescence color-switching materials. Because of the attractive application potential and the numerous underlying structure–property relationships in such materials, we investigated a series
of fluorenyl-containing tetrasubstituted ethylenes for their novel optical properties and structural features. The dyes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solKeywords: aggregation · ethylenes · luminescence · morphology · substituent effects
Introduction
shows distinct fluorescence in different polymorphs, for example, in the amorphous and crystalline state. The mechano-stimuli that can induce certain crystalline materials into the amorphous state can trigger ML. In this field a longterm goal is to develop candidates with large contrast and strong emissions. Given that many common luminogens severely decrease their luminescence in the condensed phase, thereby making them unfit for the use in efficient and highcontrast ML, aggregation-induced emission (AIE) luminogens with strong emissions in the solid state are superior candidates. Since the discovery of the piezofluorochromic phenomenon based on an AIE compound in 2010,[8] a number of AIE compounds with reversible ML have been successfully prepared by other groups.[9] The fluorescence of many such materials depends on their morphology, which shows abnormal crystallization-induced blueshift emission.[10] Researchers have checked the structures and packing motifs of the AIE materials to find correlations between structures and the AIE property.[6, 7] For the AIE materials with ML ability, the structural relationship has also been recognized on the basis of recent experimental results.[9, 11] To achieve the molecular design of promising ML materials, the structural features of the smart compounds should be thoroughly investigated along with the underlying mechanism as to why the materials change their intermolecular interactions or intramolecular conformations in response to mechanical stimuli, and how this change causes fluorescence shift should be fully understood. Here we have investigated the ML property of a series of fluorenyl-containing tetrasubstituted ethylenes. By analyzing their single-crystal XRD structures and optical and thermal properties, we discussed the effect of different substituents and the molecular arrangements on the ML behavior, as well as the solventfuming crystallization process.
Mechanochromic luminescence (ML) materials have attracted a great deal of interest because of their potential applications in sensors, security materials, and information display and storage.[1] Normally, ML materials produce clear fluorescence intensity and/or color changes as a result of the transformation of chemical or physical structures in which the transformation is sensitive to external stimuli such as mechanical forces, solvent fuming, or thermal treatment.[2–5] For example, the tuning of the emission of some organic materials was implemented through changing the chemical structures that involved the opened/closed cyclic form[2] or double-bond E/Z isomerization.[3] However, some reports focused on controlling the mode of molecular packing by means of the crystalline-to-amorphous transition[4] or the phase shift of the liquid-crystalline state.[5] Recently, researchers have begun to pay more and more attention to changing the intermolecular interactions of chromophores by means of mechano-stimuli, which is believed to be more facile when achieving highly efficient and reversible ML.[6] Up to now most research efforts have proved that the emission property of some organic solids has a close relationship with the regularity of molecular packing.[7] Researchers have encountered many cases in which the same compound [a] Y. Lv, Prof. Dr. Y. Liu, D. Guo, X. Ye, G. Liu, Prof. Dr. X. Tao State Key Laboratory of Crystal Materials Key Laboratory of Functional Crystal Materials and Devices of MOE, Shandong University Jinan, Shandong 250100 (P.R. China) E-mail: [email protected] [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201402627.
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
vent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing. Through single-crystal and X-ray diffraction (XRD) analysis, the twisted molecular geometries and loose packing motifs in the crystalline samples are believed to be the intrinsic origin of the external-stimuli-induced structural transformation.
1
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
Results and Discussion
The three dyes are readily soluble in common organic solvents such as CH2Cl2, chloroform, and THF, but not in water. They are typical AIE luminogens such as tetraphenACHTUNGREylACHTUNGREethene (TPE), which have nearly no emission in solutions but strong emission in the aggregation states. The Supporting Information shows the fluorescence change of the three samples from solution to aggregates in aqueous suspensions. The photoluminescence (PL) spectra of BBFT, BFT1, and BFT2 in THF are basically flat lines parallel to the abscissa, which reveals that they are genuinely weak emitters in the solution state. In pure THF, the quantum yields of all the three compounds are lower than 1 %. When a large amount of water is added into their solutions in THF, intense PL signals are recorded under identical measurement conditions at 515, 510, and 518 nm, respectively. After the water fraction (Wf) in the H2O/THF mixtures is larger than approximately 60 %, the dissolved molecular species start to aggregate; this is accompanied by rapid photoluminescence boosting. As shown in the Supporting Information, from the molecular solution in THF to the aggregate suspension in 95 % aqueous mixture, the PL intensities of all the three luminogens enhance more than one hundred times. In the Wf = 95 % aqueous mixtures, their fluorescence quantum yields reached 65, 58, and 60 %, respectively. The inset images in Figures S4 and S5 in the Supporting Information demonstrate the nonluminescent and emissive natures of the molecular isolated species and aggregates.[13] BBFT, BFT1, and BFT2 exhibit bright emission in the solid state. As shown in Figure 1, when excited at 365 nm, the luminogens in the crystalline and powder state display distinct fluorescence color, thus indicating a morphology-dependent luminescence. The PL spectra of the samples are shown in Figure 2. The crystals of BBFT, BFT1, and BFT2 show intense blue luminescence at 459 to 470 nm; and the as-prepared powders show greenish-yellow emission at 507 to 517 nm. The fluorescent quantum yields of the compounds in different solid states were measured by an absolute method using an integrating sphere whereby the respective yield in crystalline form is superior to that of the powder, with the data ranging from 56 to 88 %. The powder X-ray diffraction (PXRD) analysis confirmed the amorphous state of the as-prepared powders, which means the luminogens show an abnormal phenomenon of crystallizationinduced blueshift fluorescence. This stands in contrast to the well-known idea that for most common chromophores crystallization leads to emission quenching and redshift owing to strong intermolecular interactions and multiple excited-state decay pathways formed in crystals.[14, 15] According to previous studies, the fluorescence of such AIE solids can be affected by external stimuli.[6, 9, 11] We thus checked the ML behavior of the three compounds. As depicted in Figure 2, when we ground the crystalline samples of BBFT, BFT1, and BFT2 with a pestle or sheared them with a spatula, their fluorescence switched simultaneously during the process of grinding, and ultimately the entire blue-emissive samples turned into greenish ones. Figure 2 presents the PL spectra of the initial crystals and the ground powders, in
The chemical structures of the three tetrasubstituted ethylenes—1,2-bis(7-bromo-9,9-dibutylfluorenyl)-1,2-diphenylACHTUNGREethene (BBFT), 1,2-bis(9,9-dibutylfluorenyl)-1,2-diphenylACHTUNGREethene (BFT1), and 1,2-bis(2-fluorenyl-7-bromo)-1,2-diphenylethene (BFT2)—are shown in Figure 1. BBFT contains two bromo-substituted 9,9-dibutylfluorenyl units. The alkyl chains were introduced to facilitate its ability to self-assemble; and likewise the bromo atoms were incorporated to introduce more intermolecular interactions. For comparisons, BFT1, which contained only alkyl chains, and BFT2, which contained only bromo substituents, were prepared. The three compounds were all synthesized through the typical reactions of Zn/TiCl4-mediated McMurry coupling.[12] The products were purified by using silica gel column chromatography with dichloromethane/petroleum ether as the eluent and was then precipitated by pouring their solutions in CH2Cl2 into ethanol to yield the as-prepared powders. The crystals of BBFT, BFT1, and BFT2 were obtained by slow evaporation of a solution of ethanol/CH2Cl2 at room temperature. The identity and purity of the new compounds were verified by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis.
Figure 1. Chemical structures of BBFT, BFT1, and BFT2, and the corresponding fluorescent images of crystalline and as-prepared powders. Sacle bars, 100 mm.
Abstract in Chinese:
&
&
Chem. Asian J. 2014, 00, 0 – 0
Yang Liu, Xutang Tao et al.
2
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
www.chemasianj.org
Yang Liu, Xutang Tao et al.
color before and after grinding demonstrates high contrast: for BBFT, the PL redshifted about 58 nm to 517 nm from 459 nm of the crystals; for BFT1 and BFT2, the fluorescence redshifted from 473 to 507 nm, and from 464 to 516 nm, respectively. From the degree of emission shift in the ML process, we found that the incorporation of bromo substituents on the one hand makes the emission in crystals more blue and, on the other hand, redshifts the emission in the amorphous state. The fluorescence shifts of the bromo-containing compounds BBFT and BFT2 (58 and 52 nm) are clearly larger than that of BFT1 (34 nm) without bromo substituents, which is in Figure 2. Fluorescence images of a) BBFT, b) BFT1, and c) BFT2 in the grinding process and the correspondfavor of a high-contrast ML. ing fluorescence spectra of the dyes in d) crystalline, e) as-prepared powders, and f) ground powders. Like many other chromophores with ML properties, the fluorescence transition of these fluorenyl-containing ethylwhich we can see that the spectral profiles of the ground enes can be reversed by fuming under a solvent atmosphere. powders almost coincide with those of the as-prepared powAs shown in Figure 3, for the compounds BBFT and BFT1 ders, thus indicating their amorphous state. The emission with alkyl chains, the emission color of ground powders can be reversed by ethanol vapor fuming. After fumigation, their emission peaks blueshifted 51 and 35 nm, thereby resembling that of the respective initial crystals, whereas for compound BFT2 without alkyl chains, fuming by ethanol vapor could not restore the emission color, probably on account of its poor crystallization capacity. After many trials we found that the blue luminescence of the ground powder of BFT2 could be reversed by fuming it with CH2Cl2. By means of such a process of grinding and solvent fuming, the fluorescence of the three dyes could be transformed repeatedly. This fluorescence reversion is believed to be the result of an amorphous-to-crystalline transition, which is confirmed by the XRD patterns of different forms, as shown in Figure 4. We can see that both crystals and the fumed powders have sharp diffraction peaks, whereas for the ground powders, their diffraction patterns are nearly flat lines with inconspicuous broad peaks. This reveals that the crystallinity was significantly reduced through grinding to crush the structured molecular packing into disorder in the ground powders. The diffraction peaks of the fumed powders coincide with those of the initial crystals, thus implying that after being fumigated with organic solvent the molecules go back into packing in a crystalline form similar to that in crystals. Thus the morphological nature of these dyes can be distinguished by the luminance color: blue corresponds to crystalline and green corresponds to amorphous. Figure 3. PL spectra of the ground and fumed powder of a) BBFT, The effect of the solvent during fumigation is believed to b) BFT1, and c) BFT2. Inset: Photographs of ground (left) and fumed increase the molecular activity and facilitate the rearrange(right) samples under UV illumination.
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
3
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
Yang Liu, Xutang Tao et al.
and ethanol are very poor solvents, but CH2Cl2 and chloroform are good ones. However, the solvent-fuming behavior of BFT2 is different to that of BBFT and BFT1. For BFT2, CH2Cl2 and chloroform can promote the transformation from the amorphous to crystalline state, whereas ethanol cannot. We propose that whether or not a solvent vapor induFigure 4. XRD spectra of a) BBFT, b) BFT1, and c) BFT2 in different forms (crystals, ground powder, and ces crystallization or amorphifumed powder). zation is actually determined by the crystallizing ability and the crystallization habit of the specific solute in this solvent. ment of molecules from being random to ordered. With BBFT and BFT1 have four n-butyl chains, which can faciliregard to the solvent-fuming-assisted recrystallization, some tate the self-assembly activity of the molecules. Therefore, reports have proposed that all good solvents can play such under an ethanol atmosphere their molecules can be reara role in inducing crystallization.[15] However, from our exranged, whereas the significant dissolving capacity of perimental results, this might not be exact. We found that by CH2Cl2 would disturb the ordered molecular arrangement. using solvents such as methanol and ethanol as the fuming For the rigid BFT2 molecules, however, ethanol is unable to agent, the fluorescence recovery from green to blue can be promote orderly molecular movement. The activity of the realized for the amorphous powders of BBFT and BFT1. molecular arrangement is also influenced by the fuming Other solvents such as CH2Cl2 and chloroform have no such temperature. As shown in Figure S6 in the Supporting Inforeffect. Conversely, fuming with them could cause the crystalmation, the reversion speed of BBFT can be tuned by the line materials of BBFT and BFT1 to become amorphous, acfumigation temperature of the ethanol atmosphere. When companied by a fluorescence change from blue to green. As the temperature of the fuming system was elevated from 20 shown in Figure 6b, reversible fluorescence changing can be to 80 8C, the fluorescence reversion time was reduced from achieved on the BBFT film by alternately repeating ethanol and CH2Cl2 solvent fuming. In fact, for these dyes, methanol 2 h to 3 min. The higher temperature increases both the
Figure 5. a) Molecular conformation of BBFT in the crystal defined by X-ray crystallography. b) The crystal packing of the BBFT molecule. c) The C H···Br interaction (I) and d) C H···p interaction (II). The vertical distance between H and Br (I), H and the p-ring centroid (II), and the parallel neighboring fluorenyl rings are also marked.
&
&
Chem. Asian J. 2014, 00, 0 – 0
4
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
www.chemasianj.org
cious voids. Such kinds of crystal have low lattice energy, which allows them to be easily destroyed by external pressure.[5, 6] Once the lattice bindings collapse, the twisted molecular conformation constrained by the crystalline lattice can relax to a more planarized conformation, thereby generating redshifted emissions. Theoretical optimization on BBFT by using density functional theory calculations proves a more planar molecular geometry in the free isolated state than that in the X-ray crystal structure. The crystal structures of BFT1 and BFT2 are presented in the Supporting Information, which also shows the twisted structures and loose packing. In BFT1, there is only one kind of C H···p intermolecular interaction with a distance of 2.95 ; and in BFT2, only an intermolecular C H···p interaction with a distance of 2.74 formed. In a word, in this series of materials, the severe twisted molecular conformation induces a noncompact molecular packing that is easy to subject to the phase transition from crystalline to amorphous initiated by mechanical pressure. During the transition process, the planarization of the twisted molecules results in the pronounced luminescence color change, which is the origin of the ML.[6, 7] Given the ML property, we investigated their use as pressure-sensitive papers. As shown in Figure 6a, a piece of filter paper spray-coated with crystalline BBFT emits bright blue light under UV light; when inscribing the letters SDU on it with a spatula, the letters emit intense greenish light, which can be distinguished easily from the blue background. The letters can be erased upon ethanol solvent fumigation. This result demonstrates that the materials can potentially be applicable in optical recording, security inks, and latent image developers. Additionally, by making use of the reversible change in morphology induced by different solvent vapors, these materials might also be used as sensors to distinguish specific solvents (Figure 6b).
Figure 6. a) Procedures of using a crystalline BBFT film as pressure-sensitive paper: writing with a spatula and erasing by fuming with ethanol vapor. b) The different responses of BBFT film to the CH2Cl2 and ethanol vapor. Photos were taken under 365 nm UV light.
vapor pressure and the activity of molecules, thus making the speed of the phase transition faster. Up to now, the ML behavior in a number of AIE materials has been proven to result from the morphological change between crystalline and amorphous states.[6] However, it is known that it is unlikely for most other crystalline materials to be manually ground into the amorphous state, because the energy needed to destroy a crystal unit cell is immense. To learn why amorphization occurs easily in these materials, and to gain a deeper understanding of the ML mechanism, we analyzed their crystal structures. Figure 5 shows the crystal structure and packing motif of BBFT, in which the molecules adopt a highly twisted conformation. The dihedral angles between each of the two substituents of the alkene are quite large. For instance, the dihedral angles between the two fluorenyl (1 and 2) and the two phenyl (3 and 4) planes are 84.1 and 58.98, respectively. The large torsion shortens the effective conjugation length of the molecule and hence causes it to emit shorter-wavelength light in crystals. However, such a geometry hampers the close intermolecular p–p stacking and causes the molecules to adopt a loose packing in the condensed state. Therefore another characteristic of the crystal packing is the absence of strong intermolecular interactions. In addition to van der Waals forces, the molecules assemble through two primary weak intermolecular interactions that contain C H···Br (Figure 5c) and C H···p interactions (Figure 5d). Each bromo substituent is in contact with an alkyl hydrogen of another molecule to form a C H···Br interaction with an H···Br bond length of 2.82 . The C H···p interactions are formed between an aromatic hydrogen of a fluorenyl unit and another fluorenyl ring that belongs to a neighboring molecule, with a distance between H and the p-ring centroid of 2.73 . Figure 5b depicts the packing motif of BBFT, in which the molecules are packed in an ABAB (two different molecular orientations) periodic arrangement. The nearest vertical distance between two neighboring overlapped fluorenyl rings with a sliding angle of 22.778 is approximately 7.96 , which is too large to shape any p–p interactions. Thus the absence of strong intermolecular interactions leads to a loose packing motif and the appearance of many capa-
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
Yang Liu, Xutang Tao et al.
Conclusion In this report we developed a series of AIE-active fluorenylcontaining tetrasubstituted ethylenes with the aim of creating efficient and high-contrast mechanochromic luminescence materials. The luminogens show morphology-dependent fluorescence color: deep blue in crystals and green in the amorphous state. By means of mechanical grinding and solvent fuming, their morphologies transform between amorphous and crystalline, thereby resulting in emission switching between green and blue. Different substituents proved to have a clear effect on the optical and ML behaviors. By analysis of their XRD crystal structures and arrangements, the twisted molecular conformations, weak intermolecular interactions, and loose packing were found to be the common features in their structures and are responsible for the occurrence of the mechanochromic luminescence. We believe that this study will not only enrich the family of ML materials but also provide a deep understanding of the tuning of solid-state luminescent properties.
5
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
www.chemasianj.org
[6] a) Z. Chi, X. Zhang, B. Xu, J. R. Xu, Chem. Soc. Rev. 2012, 41, 3878 – 3896; b) D. R. T. Roberts, S. J. Holder, J. Mater. Chem. 2011, 21, 8256 – 8268; c) S. Perruchas, X. F. L. Goff, S. Maron, I. Maurin, F. Guillen, A. Garcia, T. Gacoin, J. Boilot, J. Am. Chem. Soc. 2010, 132, 10967 – 10969; d) Z. Yang, Z. Chi, T. Yu, X. Zhang, M. Chen, B. Xu, S. Liu, Y. Zhang, J. R. Xu, J. Mater. Chem. 2009, 19, 5541 – 5546; e) H. Ito, T. Saito, N. Oshima, N. Kitamura, S. Ishizaka, Y. Hinatsu, M. Wakeshima, M. Kato, K. Tsuge, M. Sawamura, J. Am. Chem. Soc. 2008, 130, 10044 – 10045; f) T. Lasanta, M. E. Olmos, A. Laguna, J. M. Lpez-de-Luzuriaga, P. Naumov, J. Am. Chem. Soc. 2011, 133, 16358 – 16361. [7] a) G. Li, F. Song, D. Wu, J. Lan, X. Liu, J. Wu, S. Yang, D. Xiao, J. You, Adv. Funct. Mater. 2014, 24, 747 – 753; b) A. Fukazawa, D. Kishi, Y. Tanaka, S. Seki, S. Yamaguchi, Angew. Chem. Int. Ed. 2013, 52, 12091 – 12095; Angew. Chem. 2013, 125, 12313 – 12317; c) T. Han, Y. Zhang, X. Feng, Z. Lin, B. Tong, J. Shi, J. Zhi, Y. Dong, Chem. Commun. 2013, 49, 7049 – 7051; d) B. Moulton, M. J. Zaworotko, Chem. Rev. 2001, 101, 1629 – 1658; e) P. J. Diemer, C. R. Lyle, Y. Mei, C. Sutton, M. M. Payne, J. E. Anthony, V. Coropceanu, J.-L. Brdas, O. D. Jurchescu, Adv. Mater. 2013, 25, 6956 – 6962. [8] S. J. Yoon, J. W. Chung, J. Gierschner, K. S. Kim, M. G. Choi, D. Kim, S. Y. Park, J. Am. Chem. Soc. 2010, 132, 13675 – 13683. [9] a) B. Xu, Z. Chi, J. Zhang, X. Zhang, H. Li, X. Li, S. Liu, Y. Zhang, J. R. Xu, Chem. Asian J. 2011, 6, 1470 – 1478; b) X. Luo, J. Li, C. Li, L. Heng, Y. Q. Dong, Z. Liu, Z. Bo, B. Z. Tang, Adv. Mater. 2011, 23, 3261 – 3265; c) X. Luo, W. Zhao, J. Shi, C. Li, Z. Liu, Z. Bo, Y. Q. Dong, B. Z. Tang, J. Phys. Chem. C 2012, 116, 21967 – 21972. [10] W. Yuan, Y. Tan, Y. Gong, P. Lu, J. W. Y. Lam, X. Shen, C. Feng, H. H-Y. Sung, Y. Lu, I. D. Williams, J. Sun, B. Z. Tang, Adv. Mater. 2013, 25, 2837 – 2843. [11] X. Y. Shen, Y. J. Wang, E. Zhao, W. Z. Yuan, Y. Liu, P. Lu, A. Qin, Y. Ma, J. Z. Sun, B. Z. Tang, J. Phys. Chem. C 2013, 117, 7334 – 7347. [12] a) Y. Liu, Y. Lv, X. T. Tao, B. Z. Tang, Chem. Asian J. 2012, 7, 2424 – 2428; b) Y. Liu, X. H. Chen, Y. Lv, X. T. Tao, B. Z. Tang, Chem. Eur. J. 2012, 18, 9929 – 9938; c) Y. Liu, Y. Lv, H. Xi, X. Zhang, S. Chen, J. W. Y. Lam, R. T. K. Kwok, F. Mahtab, H. S. Kwok, X. Tao, B. Z. Tang, Chem. Commun. 2013, 49, 7216 – 7218; d) Y. Liu, X. Ye, G. Liu, Y. Lv, X. Zhang, S. Chen, J. W. Y. Lam, H. S. Kwok, X. Tao, B. Z. Tang, J. Mater. Chem. C 2014, 2, 1004 – 1009. [13] a) Y. Liu, S. Chen, J. W. Y. Lam, F. Mahtab, H. S. Kwok, B. Z. Tang, J. Mater. Chem. 2012, 22, 5184 – 5189; b) X. Zhang, Z. Chi, H. Li, B. Xu, X. Li, S. Liu, Y. Zhang, J. Xu, J. Mater. Chem. 2011, 21, 1788 – 1796. [14] a) Y. Liu, X. Tao, F. Wang, X. Dang, D. Zou, Y. Ren, M. Jiang, Org. Electron. 2009, 10, 1082; b) Review: M. Shimizu, T. Hiyama, Chem. Asian J. 2010, 5, 1516 – 1531; c) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332 – 4353; d) M. S. Kwon, J. Gierschner, S. Yoon, S. Y. Park, Adv. Mater. 2012, 24, 5487 – 5492. [15] a) N. Mizoshita, T. Tani, S. Inagaki, Adv. Mater. 2012, 24, 3350 – 3355; b) X. Zhang, Z. Chi, H. Li, B. Xu, X. Li, W. Zhou, S. Liu, Y. Zhang, J. R. Xu, Chem. Asian J. 2011, 6, 808 – 811.
Experimental Section The three compounds were synthesized through the typical reactions of AlCl3-catalyzed Friedel–Crafts acylation and Zn/TiCl4-mediated McMurry coupling.[12] Details of the synthetic procedures and characterization data are presented in the Supporting Information. Crystal structure analysis was carried out with a Bruker SMART APEX-II equipped with a CCD area-detector diffractometer at 296(2) K using graphite-monochromated MoKa radiation (l = 0.71073 ) with the w scan method. The structures were solved by direct methods and refined by the full-matrix least-squares technique on F2 using SHELX programs. CCDC-909142 (BBFT), 974227 (BFT1), and 974229 (BFT2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements We thank the National Natural Science Foundation of China (grant nos. 51021062, 51303095, 50990061, 51003054, and 51272129), the Promotive Research Fund for Young Scientists of Shandong Province (BS2012L020), and the 973 Program of the Peoples Republic of China (grant no. 2010CB630702) for financial support.
[1] a) G. Zhang, J. Lu, M. Sabat, C. L. Fraser, J. Am. Chem. Soc. 2010, 132, 2160 – 2162; b) A. Pucci, F. D. Cuia, F. Signori, G. Ruggeri, J. Mater. Chem. 2007, 17, 783 – 790; c) Z. Ning, Z. Chen, Q. Zhang, Y. Yan, S. Qian, Y. Cao, H. Tian, Adv. Funct. Mater. 2007, 17, 3799 – 3807; d) A. Kishimura, T. Yamashita, K. Yamaguchi, T. Aida, Nat. Mater. 2005, 4, 546 – 549; e) S. Hirata, T. Watanabe, Adv. Mater. 2006, 18, 2725 – 2729; f) C. E. Olson, M. J. R. Previte, J. T. Fourkas, Nat. Mater. 2002, 1, 225 – 228; g) S. M. Jeong, S. Song, S. Lee, N. Y. Ha, Adv. Mater. 2013, 25, 6194 – 6200; h) Z. Zhang, B. Xu, J. Su, L. Shen, Y. Xie, H. Tian, Angew. Chem. Int. Ed. 2011, 50, 11654 – 11657; Angew. Chem. 2011, 123, 11858 – 11861. [2] a) D. A. Davis, A. Hamilton, J. Yang, L. D. Cremar, D. V. Gough, S. L. Potisek, M. T. Ong, P. V. Braun, T. J. Martnez, S. R. White, J. S. Moore, N. R. Sottos, Nature 2009, 459, 68 – 72; b) C. K. Lee, D. A. Davis, S. R. White, J. S. Moore, N. R. Sottos, P. V. Braun, J. Am. Chem. Soc. 2010, 132, 16107 – 16111. [3] A. Schçnberg, M. Elkaschef, M. Nosseir, M. M. Sidky, J. Am. Chem. Soc. 1958, 80, 6312 – 6315. [4] a) J. Wang, J. Mei, R. Hu, J. Z. Sun, A. Qin, B. Z. Tang, J. Am. Chem. Soc. 2012, 134, 9956 – 9966; b) B. Xu, Z. Chi, J. Zhang, X. Zhang, H. Li, S. Liu, Y. Zhang, J. R. Xu, Chem. Commun. 2011, 47, 11080 – 11082; c) X. Gu, J. Yao, G. Zhang, Y. Yan, D. Zhang, Adv. Funct. Mater. 2012, 22, 4862 – 4872; d) X. Zhang, Z. Chi, J. Zhang, H. Li, B. Xu, X. Li, S. Liu, Y. Zhang, J. R. Xu, J Phys Chem. B 2011, 115, 7606 – 7611. [5] a) Y. Sagara, T. Kato, Angew. Chem. Int. Ed. 2008, 47, 5175 – 5178; Angew. Chem. 2008, 120, 5253 – 5256; b) Y. Sagara, T. Kato, Angew. Chem. Int. Ed. 2011, 50, 9128 – 9132; Angew. Chem. 2011, 123, 9294 – 9298.
&
&
Chem. Asian J. 2014, 00, 0 – 0
Yang Liu, Xutang Tao et al.
Received: June 8, 2014 Published online: && &&, 0000
6
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!
FULL PAPER A glowing report: A series of fluorenyl-containing tetrasubstituted ethylenes show morphology-dependent luminescence. Their emission color can be switched between green and blue by means of mechanical grinding and solvent fuming. The transformation between crystalline and amorphous accounts for the luminescence changing (see figure).
Chem. Asian J. 2014, 00, 0 – 0
These are not the final page numbers! ÞÞ
Luminescence Yun Lv, Yang Liu,* Dan Guo, Xin Ye, Guangfeng Liu, &&&&—&&&& Xutang Tao* Mechanochromic Luminescence of Fluorenyl-Substituted Ethylenes
7
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
