Accepted Manuscript Synthesis, photophysical and thin-film self-assembly properties of novel fluorescent molecules with carbon–carbon triple bonds Qingfen Niu, Hongjian Sun, Xiaoyan Li PII: DOI: Reference:

S1386-1425(14)00854-3 http://dx.doi.org/10.1016/j.saa.2014.05.063 SAA 12225

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

28 December 2013 19 March 2014 16 May 2014

Please cite this article as: Q. Niu, H. Sun, X. Li, Synthesis, photophysical and thin-film self-assembly properties of novel fluorescent molecules with carbon–carbon triple bonds, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.05.063

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Synthesis, photophysical and thin-film self-assembly properties of novel fluorescent molecules with carbon–carbon triple bonds Qingfen Niu, Hongjian Sun, Xiaoyan Li*

School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, Shandong University, Shanda Nanlu 27, 250199 Jinan, People’s Republic of China

Abstract Three novel fluorescent molecules with carbon–carbon triple bonds 2TBEA, 2TBDA and TEPEB are successfully designed and synthesized. Their thermal, photophysical, electrochemical, electronic and thin-film self-assembly properties were characterized. Three dyes showed typical photoluminescence (PL) emission behaviors, the PL intensities firstly increased and then decreased with gradually decreasing concentration. The appealing fluorescence properties indicated that three dyes could be used as good fluorescent materials. Additionally, the thin-film self-assembly behaviors of three dyes were also investigated. The microstructures of their optical microscopy (OM) images exhibited high flexibility. Furthermore, SEM and AFM surface morphology of these self-assembly nanostructures revealed that three well-defined long-range order of rod-like and tube-like self-assembly systems exhibited interesting morphology properties. Therefore, three compounds may be of great interest for the development of organic thin-film materials.

Keywords: fluorescent molecule; thin-film self-assembly; fluorescent material; morphology; thin-film material

* To whom the correspondence should be addressed E-mail: [email protected] Telephone: +86(531)88361350 Fax number: +86(531)88564464

1

Introduction Organic π-conjugated materials have emerged as key players in the development of new generations of organic-based devices such as organic light-emitting diodes (OLEDs), lasers, organic field-effect transistors (OFETs), photovoltaic cells, molecular electronic junctions, and biosensors over the last few decades. Similarly, π-conjugated oligomers [1–5] share a large number of the properties of π-conjugated polymers with certain advantages including their well-defined structure, easier purification, fewer defects and the possibility to introduce functionalities. Applications of organic π-conjugated materials reached the commercialization stage involving the use of organic π-conjugated polymers [6–10] and molecules [11–14] as driving and switching elements in OLEDs. Additionally, another high technological relevance is the incorporation of organic π-conjugated oligomers [15–24] or polymers [25–31] as the semiconducting layer in OFETs. Currently, OLEDs and OFETs have been integrated in the fabrication of smart pixels where OLEDs are driven by organic transistors [32–35]. Thanks to the researchers, a wide variety of organic semiconductors based on π-conjugated molecules and linearly fused aromatic compounds have already been exploited [36–37]. However, there is still much going on research into the new organic π-conjugated compounds with high mobility, solubility and environmental stability, to realize their full potential in the electronic and optical devices [38–42]. Recently, thiophene-based materials have attracted increasing attention for their potential applications in the fields of organic semiconductors owing to their light

2

weight, good chemical stability, high carrier mobility and the ease of structural tuning to adjust their electronic, optical, morphological and film-formed properties [43–48]. It has been reported that oligothiophenes end-capped with strong electron donors (such

as

diphenylaminofluorenyl

hole-transporting

bis-dipolar

phenylene–thiophene

backbone

moieties)

emitters

for

containing

have

become

OLEDs

[49].

amide

moieties

highly

efficient

What

is

more,

can

also

force

self-assembling in the desired way through hydrogen bonding and dipole–dipole interactions [50]. These compounds in the thin-film state can self-assemble into well-defined long one-dimensional structures with high structural order due to the combination of the strong hydrogen bonding and π-stacking interactions. However, the morphology of the π-conjugated polymers or oligomers in cast or spin-coated film is considered to be an important factor to determine the device performances [51]. For the time being, many scientists are paying a good deal of attention to acetylenic-based organic π-conjugated polymers or oligomers for their wide applications in photovoltaic devices [52–62]. Meanwhile, a large number of researchers are interested in an increase of the open circuit voltage, which is defined as the quasi-Fermi level splitting between the donor HOMO and the acceptor LUMO. However, the specific electric parameter is involved in solar cells as the result of the electron-withdrawing nature of the C≡C group leading to an enhanced electron affinity, and consequently to a higher oxidation potential and a lower HOMO level [52–54, 63–65]. Thus materials of this type used as donors may provide a new route to the improved photovoltaic device performances. Most recently, a new class of

3

thiophene-based or biphenyl-based semiconductors containing carbon–carbon triple bonds with good self-ordering, photophysical, optical, electrochemical, electronic and film-formed properties have been investigated [66–74]. To date, the total number of the materials containing carbon–carbon triple bonds for high-performance organic devices with enhanced environmental stability is not much. Therefore, the design and synthesis of more modified thiophene–phenylene or biphenylene derivatives containing carbon–carbon triple bonds is promising approach to high-performance organic devices. Based on the published observations, the incorporation of arylene ethynylene structural motifs into organic π-conjugated systems are expected to make them more interesting and desirable properties and hence are of great interest to us. In order to design and synthesize more new compounds with carbon–carbon triple bonds, and further investigate their structure-property relationships, herein three new compounds 4-((5'-(phenylethynyl)-[2,2'-bithiophen]-5-yl)ethynyl)aniline 4,4'-([2,2'-bithiophene]-5,5'-diylbis(ethyne-2,1-diyl))dianiline

(2TBEA), (2TBDA)

and

trimethyl((4-((4'-((4-((trimethylsilyl)buta-1,3-diyn-1-yl)phenyl)ethynyl)-[1,1'-biphenyl]-4-yl)ethynyl)phenyl)ethynyl)silane (TEPEB) (Fig.1) containing carbon–carbon triple bonds were successfully designed and synthesized. The three compounds were fully characterized with respect to thermogravimetric analysis (TGA), UV–vis absorption spectroscopy, photoluminescence (PL) emission spectroscopy, cyclic voltammetry (CV), density functional theory (DFT) calculations, X-ray powder diffraction (XRD). Furthermore, their thin-film self-assembly morphology properties

4

of these compounds were characterized by optical microscope (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The three fluorescent dyes exhibited good photophysical, electrochemical and thin-film self-assembly morphology properties. However, these good properties of three compounds with carbon–carbon triple bonds may be of great interest for the development of photovoltaic materials and organic thin-film materials.

Fig. 1

Experimental Materials 2-Bromothiophene and 2,5-dibromothiophene were purchased from the China Medicine Shanghai Chemical Reagent Corp, China. All other chemicals were purchased from Aldrich and Acros and used as received without further purification. N-iodosuccinimide

(NIS)

[75],

2,2'-bithiophene

4-((5'-iodo-[2,2'-bithiophen]-5-yl)ethynyl)aniline

[77],

(2T)

4-ethynylaniline

[76], and

4-((trimethylsilyl)ethynyl)aniline [78] were prepared according to the published procedures. Catalyst Pd(PPh3)2Cl2 [79] was prepared from PdCl2 according to the published

literature.

4,4'-Diethynyl-1,1'-biphenyl

[80]

was

prepared

from

4,4'-diiodo-1,1'-biphenyl according to the published literature. Solvents were purified and dried according to the standard procedures.

5

Measurements and characterizations 1

H and

13

C NMR spectra were recorded on a Bruker AVANCE 300 NMR

Spectrometer with CDCl3 as the solvent with tetramethylsilane (TMS) as an internal reference. LC-MS were obtained from Agilent 6510 Accurate-Mass Q-TOF LC/MS system. Infrared measurements with the KBr pellet technique were performed within the 4000–400 cm–1 region on a Bruker ALPHA FT-IR spectrometer. Ultraviolet absorption (UV) spectra of these samples (CHCl3 solution) were recorded using a Hitachi U-4100 spectrometer. Photoluminescence (PL) measurements were recorded on a Hitachi F-4500 fluorescence spectrophotometer with a 150 W Xe lamp. Cyclic voltammetry (CV) measurement was performed on a CHI832 electrochemical instrument with a three-electrode cell in a solution of 0.1 M tetrabutylammonium perchlorate (n-Bu 4NClO4) in anhydrous dichloromethane at room temperature under nitrogen atmosphere with a scan rate of 100 mV/s. The working electrode was glass–carbon electrode, the counter electrode was a platinum wire, and the reference electrode was Ag/AgCl (Ag in 0.1 M AgNO3 solution of MeCN) which was separated by a diaphragm. Ferrocene–ferrocenium (Fc/Fc+) couple was chosen as internal standard. Thermogravimetric analysis (TGA) measurements were obtained by TA Q500 instrument with heating rate of 10 °C/min under nitrogen condition from room temperature to 800 °C at ambient pressure. OM was performed on a BX-51 polarization optical microscope (Olympus, Japan). The X-ray powder diffraction was carried out on powered samples via BRUKER D8 advanced diffractometer (40 mA, 40 kV) equipped with monochromator Cu Kα radiation (λ = 1.54 Å) over the 2θ range

6

of 10° to 60°. The atomic force microscopy (AFM) images were obtained by using a Digital Instruments (DI) Dimension 3100 operating in tapping mode. Scanning electron microscope (SEM) measurements were performed on a JEOL JSM-7600F emission scanning electron microscope. Thin-layer chromatography (TLC) was carried out with silica gel GF254 covered on plastic sheets and visualized by UV light, and flash column chromatographic separation was performed over silica gel.

Fluorescence quantum yield The ability for the molecules to emit the absorbed light energy is characterized quantitatively by the fluorescence quantum yield (Φ). Quantum yield was determined by the relative comparison procedure, using quinine sulfate (Φ = 0.55) as standard [81]. For all the measurements of fluorescence spectra, scan speed was 240 nm min-1 using a quartz cell of 1 cm optical path length. And the UV–vis absorption spectra were recorded in range of 600–200 nm with spectral resolution 1 nm in a standard 1 cm path length quartz cell, scan speed was 300 nm min-1. Firstly, the blank solution of sample was performed under the same condition to realize the baseline corrections. Taken the concentration (5.0 × 10–4 M) of the samples as the original solution, different concentrations (from 5.0 × 10 –4 to 1.0 × 10 –8 M) were diluted. The absorption intensity was varied by changing the concentration of the CHCl3 solution. Increasing concentration led to increasing absorption intensity, until coverages of abs > 0.1 at excitation were obtained. The general equation used in the determination of relative quantum yields from earlier research was given (Eq.1) [82].

7

ΦFu =

(ΦFs )( FAu )( As)(η u2 ) ( FAs )( Au )(η 2s )

(Eq.1)

In the equation (1), ΦF = fluorescence quantum yield; FA = integrated area under the corrected emission spectrum; A = absorbance at the excitation wavelength; ƞ = the refractive index of the solution; and the subscripts u and s refer to the unknown and the standard, respectively.

Synthesis ((4-iodophenyl)ethynyl)trimethylsilane (3). The procedure was modified by us. A

500-mL

round-bottomed

flask

was

charged

with

water

(200

mL),

4-((trimethylsilyl)ethynyl)aniline (8.4 g, 44 mmol), and stirred 15 min. Then the mixture was added HCl (20.5 mL ,12 M ) and stirred 10 min. The reaction was cooled to 0 oC, and the solution of NaNO2 (3.96 g, 57 mmol) was added dropwise slowly. The reaction in an ice bath was stirred for 30 min. The ice bath was replaced with an ambient temperature water bath and stirred for an additional 30 min. After extraction with dichloromethane (3 × 100 mL), the combined water extracts were added another 1L roundbottomed flask in an ice bath and stirred for 10 min. The solution of KI (11.4 g, 69 mmol) was added dropwise slowly at 0 °C. The reaction mixture was allowed to reach the room temperature and stirred 6 h. The aqueous layer was extracted with diethylether. The combined organic layers were washed with brine and dried with magnesium sulfate. After evaporation of the solvent, the crude product was purified by column chromatography on alumina with petroleum ether as eluent to afford compound ((4-iodophenyl)ethynyl)trimethylsilane (11.3 g, 85%) as white solid. IR 8

(KBr, cm–1) ν = 2918, 2725, 2161, 1600, 1463, 1365, 1250, 1169, 951, 842, 750, 723, 556, 471; 1H NMR (300 MHz, CDCl3, ppm) δ 0.24 (s, 9H), 7.18 (d, J = 9.0 Hz, 2H), 7.63 (d, J = 9.0 Hz, 2H); 13C NMR (75 MHz, CDCl3, ppm) δ –0.6, 93.9, 95.4, 103.5, 122.2, 132.9, 136.9. 4-((5'-(phenylethynyl)-[2,2'-bithiophen]-5-yl)ethynyl)aniline Following

the

Sonogashira

coupling

(2TBEA). procedure,

4-((5'-iodo-[2,2'-bithiophen]-5-yl)ethynyl)aniline (1) (5.0 g, 12.3 mmol) was dissolved in dry triethylamine (50 mL) and dry THF (30 mL) under an atmosphere of nitrogen. Copper(I) iodide (47.0 mg, 0.25 mmol), triphenylphosphine (64.5 mg, 0.25 mmol) and dichlorobis(triphenylphosphine)palladium(II) (87.8 mg, 0.12 mmol) were added to the stirred solution. Phenylacetylene (1.25 g, 12.3 mmol) was dropped in and the mixture was heated to 50 °C for 12 h. After cooling, the formed precipitate of triethylamine hydroiodide was filtered off and washed with diethyl ether. The combined filtrates were evaporated under reduced pressure, and the crude product was purified by silica column chromatography eluting with petroleum ether/ethyl acetate (V : V = 5 : 1) to afford compound 2TBEA (3.2 g, 68%) as bright yellow crystals; m.p. 151–153 oC; IR (KBr, cm–1) ν = 3326, 3210, 3062, 2979, 2933, 2675, 2193, 1610, 1521, 1444, 1393, 1299, 1173, 1030, 834, 801, 754, 695, 523; 1H NMR (300 MHz, CDCl3, ppm) δ 3.88 (s, 2H), 6.65 (dd, J = 6.0 Hz, 2H), 7.09 (d, J = 3.0 Hz, 2H), 7.13 (d, J = 6.0 Hz, 1H), 7.20 (d, J = 3.0 Hz, 1H), 7.33 (t, J = 3.0 Hz, 1H), 7.36–7.42 (m, 4H), 7.53 (d, J = 3.0 Hz, 1H), 7.55 (d, J = 6.0 Hz, 1H );

13

C NMR (75 MHz, CDCl3,

ppm) δ 80.54, 82.68, 94.50, 95.54, 112.04, 114.81, 122.38, 122.86, 123.82, 124.05,

9

128.48, 128.60, 131.47, 132.03, 132.89, 132.97, 137.27, 138.42, 147.05; HRMS (ESI) calcd. for C20H12S3 [M+] 382.0679, found 382.0663. 4,4'-([2,2'-bithiophene]-5,5'-diylbis(ethyne-2,1-diyl))dianiline Compound

2TBDA

was

synthesized

(2TBDA). from

4-((5'-iodo-[2,2'-bithiophen]-5-yl)ethynyl)aniline (1) (4.9 g, 12.0 mmol) and 4-ethynylaniline (1.4 g, 12.0 mmol) by the same procedure as compound 2TBEA. The crude product was purified by silica column chromatography eluting with petroleum ether/ethyl acetate (V : V = 3 : 1) to afford compound 2TBDA (3.1 g, 66%) as bright yellow crystals; m.p. 149–152 oC; IR (KBr, cm–1) ν = 3349, 3209, 3078, 3035, 2958, 2927, 2854, 2194, 1603, 1499, 1434, 1354, 1282, 1179, 884, 830, 795, 752, 692, 641, 529, 501, 410; 1H NMR (300 MHz, CDCl3, ppm) δ 3.84 (s, 4H), 6.47 (d, J = 9.0 Hz, 1H), 6.63 (d, J = 6.0 Hz, 3H), 6.83 (d, J = 3.0 Hz, 1H), 6.98 (d, J = 6.0 Hz, 1H), 7.08 (d, J = 3.0 Hz, 1H), 7.15 (d, J = 3.0 Hz, 1H), 7.32 (d, J = 9.0 Hz, 3H), 7.41 (d, J = 9.0 Hz, 1H);

13

C NMR (75 MHz, CDCl3, ppm) δ 75.00, 84.45, 113,74,

114.29, 114.64, 119.94, 122.20, 124.19, 128.94, 130.72, 130.86, 132.96, 133.47, 137.81. Trimethyl((4-((4'-((4-((trimethylsilyl)buta-1,3-diyn-1-yl)phenyl)ethynyl)-[ 1,1'-bi-phenyl]-4-yl)ethynyl)phenyl)ethynyl)silane (TEPEB). Compound TEPEB was synthesized from 4,4'-diethynyl-1,1'-biphenyl (2) (2.0 g, 9.9 mmol) and ((4-iodophenyl)ethynyl)trimethylsilane (3) (5.9 g, 19.8 mmol) by the same procedure as compound 2TBEA. The crude product was purified by silica column chromatography eluting with petroleum ether/ethyl acetate (V : V = 25 : 1) to afford

10

compound TEPEB (3.5 g, 65%) as white solid; m.p. 136–137 oC; IR (KBr, cm–1) ν = 3073, 2958, 2924, 2853, 2156, 1903, 1576, 1477, 1386, 1248, 1215, 1054, 1003, 844, 817, 758, 699, 656, 527; 1H NMR (300 MHz, CDCl3, ppm) δ 0.26 (s, 18H), 7.31 (d, J = 9.0 Hz, 4H), 7.51 (dd, J1 = J2 = 9.0 Hz, 8H), 7.76 (d, J = 9.0 Hz, 4H); 13C NMR (75 MHz, CDCl3, ppm) δ 78.25, 83.46, 94.60, 95.98, 104.08, 121.57, 122.71, 127.00, 132.74, 133.52, 137.46, 140.60.

Results and discussion Synthesis and characterization Scheme 1 illustrates the synthetic routes for three fluorescent molecules containing carbon–carbon triple bonds 2TBEA, 2TBDA and TEPEB. Three compounds were prepared by the Sonogashira coupling reaction. The synthetic reactions were controlled by TLC. These compounds are readily soluble in common solvents such as THF, diethyl ether, dichloromethane and chloroform, allowing them to be easily purified by column chromatography. The objective products were characterized by IR, NMR and LC-MS. The results are consistent with the expected chemical structures.

Scheme 1 Thermotropic properties Thermal property is essential for the fabrication of the device. The thermal properties of the fluorescent molecules 2TBEA, 2TBDA and TEPEB were evaluated

11

by means of TGA under nitrogen atmosphere and their TGA thermograms are shown in Fig. 2. TGA was performed under standard pressure to show the temperatures at which molecular components evolve from a sample. The TGA profiles of 2TBEA and 2TBDA show 5% weight loss until 183 oC, 37% weight loss over a range of 790 °C and 5% weight loss until 209 oC, 37% weight loss over a range of 793 °C, respectively. However, the profile of TEPEB shows 5% weight loss until 147 oC, 91% weight loss over a range of 791 °C.

Fig. 2

Photophysical properties Absorption spectra Normalized UV–Vis absorption spectra of three fluorescent molecules 2TBEA, 2TBDA and TEPEB were recorded in chloroform solution (C = 1.0 × 10–5 M) shown in Fig. 3(a). Each oligomer shows one broad absorption band which is around at 300–500 nm and the absorption maximum was 388 nm for 2TBEA, 398 nm for 2TBDA, and 304 nm for TEPEB, respectively. The molar extinction coefficient (ɛ) value of compound 2TBEA, 2TBDA and TEPEB in CHCl3 was 4.40, 5.13 and 2.39 (104 M-1 cm-1), respectively. The wavelength band is a dipole-allowed, π–π* electron transition absorption band of the conjugated π-electron system of the core of the mesogens. This band corresponds to the transition from the ground state to the lowest excited singlet state of the molecule. Owing to the similar structure, 2TBEA and

12

2TBDA exhibit similar π–π* electron transition peaks located in the range of 388–398 nm. It is clearly seen from Fig. 3(a) that the absorption maximum of π–π* transition was red-shifted from 388 nm for 2TBEA to 398 nm for 2TBDA. This may be attributed to the π-conjugation length and the substituent effect of amino group. All of the wavelength ranges play an important role in the photovoltaic comparison conversion. Therefore, the HOMO–LUMO gaps in solution obtained from the maximum of absorption are 3.20 eV for 2TBEA, 3.12 eV for 2TBDA, and 4.08 eV for TEPEB, respectively (Table 1). In order to further investigate the effect of concentration on the absorption maximum, we observed the absorption spectra of 2TBEA, 2TBDA and TEPEB in chloroform solution with different concentrations from 1.0 × 10–6 to 1.0 × 10–4 M shown in Fig. 3(b). With the increasing concentration of 2TBEA and 2TBDA, the absorption maximum were red shift from 371 to 402 nm and 375 to 405 nm, respectively. For TEPEB, the absorption maximum was also red shift from 296 to 318 nm with the increasing concentration. Based on the results, the three dyes exhibited J-aggregate characteristics, because of their red shift relative to the corresponding spectra in the dilute CHCl3 solution [83].

Fig. 3(a) Table 1 Fig. 3(b)

13

Photoluminescence (PL) emission spectra The chloroform solution containing 2TBEA or 2TBDA exhibited a bright green-yellow fluorescence even under daylight condition. PL emission spectra of 2TBEA, 2TBDA and TEPEB were measured in chloroform (C = 5.0 × 10–6 M) shown in Fig. 4(a). Three fluorescent dyes exhibited one pronounced peak and the corresponding PL emission maximal wavelengths are located at 494, 499 and 364 nm, respectively, and their excitation wavelengths are at 320, 330 and 304 nm, respectively. From Fig. 4(a), it is well worth noting that 2TBDA shows a broader band and the fluorescence intensity is much stronger than that of 2TBEA. This phenomenon may be attributed to the substituent effect of amino group. Compared with our recent work with analogous amino-functionalized groups substituted compounds such as 3TEA and I2TEA [77], 2TBDA exhibited the stronger fluorescence intensity. This result also indicates that their structure–property relationships of the novel organic π-conjugated planar molecule on the conjugated backbone by acetylenic spacers, thiophene-functionalized and amino-functionalized groups could effectively influence the fluorescence intensities in the emission spectra. In other words, the D–π–A–π–D structured organic dye 2TBDA based on NH2 as donor units and 2T as acceptor units with acetylenic spacers π-conjugated chain between them exhibits excellent luminescent properties. In order to understand the shape and wavelength of absorption and fluorescence band, the excitation spectra of TEPEB were measured in chloroform (C = 1.0 × 10–5 M) (Fig. 4(b)). Both absorption and excitation spectrum are almost mirror-symmetric.

14

Fig. 4(a) Fig. 4(b)

Effect of concentration on the emission spectra To further investigate the effect of concentration on the fluorescence emission intensity, we observed the PL emission spectra of 2TBEA, 2TBDA and TEPEB in chloroform solution with different concentrations from 1.0 × 10–8 to 5.0 × 10–4 M shown in Fig. 5. Their corresponding fluorescence quantum yield (Φ) values were presented in Table 2. The PL emission spectra of 2TBEA showed one emission band and one emission peak in the range of 425–625 nm. The emission maximal peak centered at ca. 494 nm in the range of the different concentrations. The fluorescence intensities of 2TBEA in chloroform increased significantly (Φ value from 0.21 to 0.70) with the increasing concentration from 1.0 × 10 –8 to 1.0 × 10–6 M. This phenomenon may be due to larger amount of fluorescent molecules. However, the fluorescence intensities decreased significantly (Φ value from 0.64 to 0.23) with the the increasing concentration from 5.0 × 10–6 to 5.0 × 10–4 M. This result may be due to self-quenching between the neighboring molecules. For 2TBDA, the emission spectra exhibited one emission band in the range of 430–600 nm and showed one emission peak centered at ca. 499 nm with the concentration from 5.0 × 10–4 to 5.0 × 10–6 M. However, the emission spectra exhibited two emission peaks with the concentration from 1.0 × 10–6 to 1.0 × 10 –8 M. The two peaks are located at 464 and

15

489 nm and the emission maximal peak centered at 464 nm. The fluorescence intensities of 2TBDA in chloroform increased significantly (Φ value from 0.21 to 0.75) with the increasing concentration from 1.0 × 10–8 to 5.0 × 10–6 M, however, the fluorescence intensities significantly decreased (Φ value from 0.61 to 0.24) with the increasing concentration from 1.0 × 10–5 to 5.0 ×10 –4 M. Likewise, the phenomena could be induced by the the concentration aggregate-enhanced emission (AEE) effect [84] and aggregation-caused quenching (ACQ) effect [85]. The novel organic dye 2TBEA and 2TBDA showed good fluorescence properties that could be applied in the optoelectronic field. For TEPEB, the emission spectra showed one emission band in the range of 330–450 nm and two emission peaks centered at ca. 364 and 352 nm. The fluorescence intensities of TEPEB in chloroform increased significantly (Φ value from 0.09 to 0.51) with the increasing concentration from 1.0 × 10–8 to 1.0 × 10–5 M. However, the fluorescence intensities decreased significantly (Φ value from 0.35 to 0.27) with the increasing concentration from 5.0 × 10 –5 to 5.0 × 10–4 M. The similar phenomena may be due to the AEE and ACQ effects. However, the molecules with aggregation-induced emission (AIE) properties have drawn more and more attention because of their enhanced emission in the aggregates. Taking advantage of the AEE effect, a variety of fluorogens with emission efficiencies up to unity in the aggregate state have been developed for applications as chemical sensors, biological probes, and active layers in OLEDs [84,86−88]. Currently, AIE has turned one of the most intriguing phenomena to achieve solid-state luminescent materials, because none missive molecules in the solution state are induced to emit intensely by aggregates.

16

Additionally, these findings can provide a new approach to adjust the fluorescent properties of AIE molecules.

Fig. 5 Table 2

Theoretical calculations In order to gain insight into the geometrical configuration and photophysical properties, the ground-state optimized geometries and electronic structures of compounds 2TBEA, 2TBDA and TEPEB were calculated with Gaussian 03 software by making full use of density functional theory (DFT) based on the Becke’s three parameter gradient-corrected functional (B3LYP) with a polarized 6-31G(d) basis [89]. The geometries of ground-state optimized structures and the electron-density distribution of HOMO, HOMO–1 and LUMO, LUMO+1 of optimized structures are showed in Figs. 6 and 7, respectively. Fig. 6 illustrates that compounds 2TBEA and 2TBDA are good planar structures and TEPEB is a good linear molecule. The HOMO, HOMO–1 and LUMO, LUMO+1 energies and energy band gaps calculated by DFT were listed in Table 1. The DFT calculated results show amino substitution on the phenyl ring, however, destabilized the LUMOs of compounds 2TBEA and 2TBDA. Fig. 6 Fig. 7

17

Electrochemical properties The electrochemical properties of three dyes 2TBEA, 2TBDA and TEPEB were measured by cyclic voltammetry in dichlorometane (C = 5.0 × 10–3 M) as shown in Fig. 8. Three compounds showed irreversible redox properties. The oxidation potentials (Eox) calculated directly from onset potential of cyclic voltammograms oxidative E1/2 values were 1.19 V for 2TBEA, 1.42 V for 2TBDA and 0.45 V for TEPEB, with the corresponding HOMO energy levels as −5.99, −6.22 and −5.25 eV, respectively. The LUMO energy levels were calculated from HOMO and optical band gap values. Hence, the corresponding LUMO energy levels were −2.79, −3.10 and −1.17 eV, respectively (Table 1). Their optical and electrochemical properties of three dyes may be the important characteristics in the conceptions of materials in photovoltaic applications [90].

Fig. 8

X-ray powder diffraction (XRD) 2TBEA, 2TBDA and TEPEB were characterized by powder XRD at room temperature with 2θ from 10° to 60°. Three oligomers are highly ordered and crystalline as evidenced in XRD profiles. The data of XRD of three dyes are listed in Table 3. In the case of 2TBEA, the X-ray profile in Fig. 9 exhibits seven peaks with the 2θ at 17.01, 19.75, 20.25, 22.00, 28.12, 37.96 and 48.64 o. The peaks at larger

18

angles are attributed to higher-order reflections, up to the seventh order. The seven intralayer spacing were determined to be 5.21, 4.49, 4.33, 4.04, 3.17, 2.37 and 1.87 Ǻ. Likewise, the X-ray profiles of dyes 2TBEA and 2TBDA display six and eight peaks, respectively. When compared with 2TBEA and 2TBDA, the peaks of TEPEB X-ray profile are quite strong and sharp. The result indicates that TEPEB exhibits higher degree of lamellar ordering and better crystallinity than 2TBEA and 2TBDA. From the results of XRD, it can be concluded that these molecules could form well-ordered thin films when deposited on the substrate.

Fig. 9 Table 3

Self-Assemblies behaviors of three fluorescent molecules Optical microscopy (OM) images Evaporation-induced

self-assembly

(EISA)

is

unique

in

offering

anonlithographic route to generating well-organized patterns with a variety of architectures. Optical microscopy measurements of these self-assemblies in the thin-film state was shown in Fig. 10. The OM images of 2TBEA, 2TBDA and TEPEB obtained by EISA through directly precipitated on the slide substrate from 1 mg/mL chloroform solution at room temperature. These precipitations of three molecules from solution formed highly flexible microribbons. However, the well-defined self-assembly microstructures of three dyes showed different flexibility.

19

Compared with 2TBEA and TEPEB, the microstructure of 2TBDA showed the higher flexibility, and even bent themselves into cycles. The difference in the flexibility of these analogous compounds is closely related to the variation in the intermolecular interaction [91]. While, the self-assembly microstructures of 2TBEA and 2TBDA exhibited high flexibility owing to the weak intermolecular interaction.

Fig. 10

Surface self-assembly thin-film morphology To further investigate the surface self-assembly morphology of these thin films, the SEM images of 2TBEA, 2TBDA and TEPEB directly precipitated on the Si/SiO2 substrate in air from 1 mg/mL chloroform solution are shown in Fig. 11. The surface patterns of three dyes were different from each other. Compounds 2TBEA and 2TBDA easily self-assembled into well-defined rod-like 1D microstructures induced by π–π stacking, and the surface of the self-assembled microribbons was made up of thousands of well-ordered lamellas similar to the well-defined spine shape. The two compounds in the thin-film state can self-assemble into well-defined 1D structures with high structural order due to the π-stacking interaction. However, TEPEB self-assembled into smooth-faced tube-shaped 1D microstructures. Compared with 2TBEA, well-ordered lamellas of 2TBDA were parallel to each other and well separated from neighboring lamellas. This may be due to lower surface energy of 2TBDA with the D–π–A–π–D structured system, however, this could effectively

20

improve alignment behavior and increase phase separation. Fig. 11 In order to further verify the surface morphology of the self-assembly thin films, the AFM images of three dyes are shown in Fig. 12. The surface self-assembly morphology of 2TBEA and 2TBDA showed well-fined microstructures with well-ordered lamellas in good connectivity. Comparing with I2TEA [77], compounds 2TBEA and 2TBDA exhibited more highly thin-film self-assembly performance because of their well-fined and even well-ordered self-assembly microstructers. This phenomenon may be attributed to the lower surface energy. Meanwhile, this result further suggested that the surface energy became lower if we expanded the π-conjugation system. However, compound TEPEB exhibited smooth-paced regular self-assembly microstructure. This could improve charge-carrier mobilities to a large extent. From the results of SEM and AFM, 2TBEA and 2TBDA displayed interesting and intriguing shapes. From Fig. 12, 2TBEA and 2TBDA showed different distances of the adjacent lamellas and the lengths of the lamellas. The distances of the adjacent lamellas are ca. 40 nm for 2TBEA and 150 nm for 2TBDA. While, the lengths of the lamella for 2TBEA and 2TBDA are ca. 790 nm and 1.9 µm, respectively. It is well worth noting that the surface self-assembly morphology of 2TBDA and TEPEB exhibited more elevated arrangement and better connectivity than that of 2TBEA. The result may be induced by the lower surface energy of 2TBDA and TEPEB.

Fig. 12

21

Conclusions In conclusion, in this work, we have successfully synthesized three novel fluorescent molecules containing carbon–carbon triple bonds 2TBEA, 2TBDA and TEPEB. Their thermal, photophysical and thin-film self-assembly properties were studied. Their PL emission spectra revealed that three molecules exhibited good fluorescence properties used as luminescent materials. XRD analysis demonstrated that three fluorescent molecules possess a high degree of crystallinity. Their OM microstructures of three dyes exhibited high flexibility. Furthermore, the surface self-assembly morphology of 2TBEA and 2TBDA have well-fined microstructures with well-ordered lamellas in good connectivity and extremely interesting shapes. What is more, 2TBDA displayed more intriguing self-assembly properties than that of 2TBEA due to the lower surface energy. However, the unique or even enhanced self-assembly morphology properties of three compounds may be of great interest for the development of organic thin-film materials.

Acknowledgements We gratefully acknowledge the support by NSF China No. 21172132, the program of Shandong Province No. 2011GGX1023 and the excellent graduate student scientific research innovation fund of Shandong University No.yzc10026. Dr. Xiaoli Zhang, Qingbin Xue, Xiuling Jiao, Shengyu Feng are thanked for the help in the measurements of CV, POM, XRD, UV–vis and PL.

22

References [1] S. Ellinger, U. Ziener, U. Thewalt, K. Landfester, M. Moeller, Chem. Mater. 19 (2007) 1070–1075. [2] N. Kiriy, V. Bocharova, A. Kiriy, M. Stamm, F.C. Krebs, H.-J. Adler, Chem. Mater. 16 (2004) 4765–4771. [3] S. Ellinger, K.R. Graham, P.J. Shi, R.T. Farley, T.T. Steckler, R.N. Brookins, et al. Chem. Mater. 23 (2011) 3805–3817. [4] D. V. Anokhin, M. Defaux, A. Mourran, M. Moeller, Y. N. Luponosov, O. V. Borshchev,

A. V.

Bakirov,

M.

A. Shcherbina,

S.

N. Chvalun,

T.

Meyer-Friedrichsen, A. Elschner, S. Kirchmeyer, S. A. Ponomarenko, D. A. Ivanov, J. Phys. Chem. C 116 (2012) 22727–22736. [5] H. Zhuang, Q. Zhou, Y. Li, Q. Zhang, H. Li, Q. Xu, N. Li, J. Lu, L. Wang, ACS Appl. Mater. Interfaces 6 (2014) 94–100. [6] R.H. Friend, R.W. Gymer, A.B. Holmes, J.H. Burroughes, R.N. Marks, C. Taliani, D.D.C. Bradley, D.A. dos Santos, M. Lögdlund, W.R. Salaneck, Nature 397 (1999) 121–128. [7] J.H. Burroughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, R.H. Friend, P.L. Burn, A.B. Holmes, Nature 347 (1990) 539–541. [8] S.C. Lo, P.L. Burn, Chem. Rev. 107 (2007) 1097–1116. [9] S.-H. Hwang, C.N. Moorefield, G.R. Newkome, Chem. Soc. Rev. 37 (2008) 2543–2557. [10] I. Osken, A.S. Gundogan, E. Tekin, M.S. Eroglu, T. Ozturk, Macromolecules 46

23

(2013) 9202–9210. [11] C.W. Tang, S.A.Van Slyke, Appl. Phys. Lett. 5 (1987) 913–915. [12] J.R. Sheats, H. Antoniadis, M. Hueschen, W. Leonard, J. Miller, R. Moon, D. Roitman, A. Stocking, Science 273 (1996) 884–888. [13] S. Xue, S. Liu, F. He, L. Yao, C. Gu, H. Xu, Z. Xie, H. Wu, Y. Ma, Chem. Commun. 49 (2013) 5730–5732. [14] H. Lee, G. Cho, S. Woo, S. Nam, J. Jeong, H. Kim, Y. Kim, RSC Adv. 2 (2012) 8762–8767. [15] F. Garnier, R. Hajlaoui, A. Yassar, P. Srivastava, Science 265 (1994) 1684–1686. [16] A. Dodabalapur, L. Torsi, H.E. Katz, Science 268 (1995) 270–271. [17] H.E. Katz, J. Mater. Chem. 7 (1997) 369–376. [18] G. Horowitz, Adv. Mater. 10 (1998) 365–377. [19] S.F. Nelson, Y.-Y. Lin, D.J. Gundlach, T.N. Jackson, Appl. Phys. Lett. 72 (1998) 1854–1856. [20] H. E. Katz, Z. Bao, J. Phys. Chem. B 104 (2000) 671–678. [21] H. E. Katz, A. J. Lovinger, J. Johnson, C. Kloc, T. Siegrist, W. Li, Y.-Y. Lin, A. Dodabalapur, Nature 404 (2000) 478–481. [22] S. Handa, E. Miyazaki, K. Takimiya, Y. Kunugi, J. Am. Chem. Soc. 129 (2007) 11684–11685. [23] R.T. Weitz, K. Amsharov, U. Zschieschang, E.B. Villas, D.K. Goswami, M. Burghard, H. Dosch, M. Jansen, K. Kern, H. Klauk, J. Am. Chem. Soc. 130 (2008) 4637–4645.

24

[24] Y. Ie, M. Ueta, M. Nitani, N. Tohnai, M. Miyata, H. Tada, Y. Aso, Chem. Mater. 24 (2012) 3285–3293. [25] H. Sirringhaus, P.J. Brown, R.H. Friend, M.N. Nielsen, K. Bechgaard, B.M.W. Langeveld-Voss, A.J.H. Spiering, R.A.J. Janssen, E.W. Meijer, P. Herwig, D.M. de Leeuw, Nature 401 (1999) 685–688. [26] Z. Bao, Adv. Mater. 12 (2000) 227–230. [27] H. Yan, Y. Zheng, R. Blache, C. Newman, S. Lu, J. Woerle, A. Facchetti, Adv. Mater. 20 (2008) 3393–3398. [28] M.J. Panzer, C.D. Frisbie, J. Am. Chem. Soc. 129 (2007) 6599–6607. [29] A. Laiho, H.T. Nguyen, H. Sinno, I. Engquist, M. Berggren, P. Dubois, O. Coulembier, X. Crispin, Macromolecules 46 (2013) 4548–4557. [30] S.N. Bhat, R. Di Pietro, H. Sirringhaus, Chem. Mater. 24 (2012) 4060–4067. [31] A. Facchetti, Chem. Mater. 23 (2011) 733–758. [32] A. Dodabalapur, Z. Bao, A. Makhija, J.G. Laquindaum, V.R. Raju, Y. Feng, H. E. Katz, J. Rogers, Appl. Phys. Lett. 73 (1998) 142–144. [33] H. Sirringhaus, N. Tessler, R.H. Friend, Science 280 (1998) 1741–1744. [34] J.-S. Kim, L. Lu, P. Sreearunothai, A. Seeley, K.-H. Yim, A. Petrozza, C.E. Murphy, D. Beljonne, J. Cornil, R.H. Friend, J. Am. Chem. Soc. 130 (2008) 13120–13131. [35] J. Mei, Y. Diao, A.L. Appleton, L. Fang, Z. Bao, J. Am. Chem. Soc. 135 (2013) 6724–6746. [36] R.A. Murphy, J.M.J. Fréchet, Chem. Rev. 107 (2007) 1066–1096.

25

[37] L. Maggini, D. Bonifazi, Chem. Soc. Rev. 41 (2012) 211–241. [38] H. Meng, F. Sun, M.B. Golfinger, G.D. Jaycox, Z. Li, W.J. Marshall, G.S. Blackman, J. Am. Chem. Soc. 127 (2005) 2406–2407. [39] C. Videlot-Ackermann, J. Ackermann, H. Brisset, K. Kawamura, N. Yoshimoto, P. Raynal, A.E. Kassmi, F. Fages, J. Am. Chem. Soc. 127 (2005) 16346–16347. [40] C. Zhao, X. Chen, C. Gao, M.-K. Ng, F. Ding, K. Park, Y. Gao, Synth. Met. 159 (2009) 995–1001. [41] C.E. Mauldin, K. Puntambekar, A.R. Murphy, F. Liao, V. Subramanian, J.M.J. Fréchet, D.M. DeLongchamp, D.A. Fischer, M.F. Toney, Chem. Mater. 21 (2009) 1927–1938. [42] C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 112 (2012) 2208–2267. [43] D. Fichou, C. Ziegler, Handbook of Oligo- and Polythiophenes (1999) 183–282. [44] D. Fichou, J. Mater. Chem. 10 (2000) 571–588. [45] I. Osaka, R.D. McCullough, Acc. Chem. Res. 41 (2008) 1202–1214. [46] A. Marrocchi, D. Lanari, A. Facchetti, L. Vaccaro, Energy Environ. Sci. 5 (2012) 8457–8474. [47] E.V. Canesi, D. Fazzi, L. Colella, C. Bertarelli, C. Castiglioni, J. Am. Chem. Soc. 134 (2012) 19070–19083. [48] T. Higashihara, M. Ueda1, Macromolecular Res. 21 (2013) 257–271. [49] Z.H. Li, M.S. Wong, H. Fukutani, Y. Tao, Chem. Mater. 17 (2005) 5032–5040. [50] N. Kiriy, V. Bocharova, A. Kiriy, M. Stamm, F.C. Krebs, H.-J. Adler, Chem. Mater. 16 (2004) 4765–4771. 26

[51] L.-L. Chua, J. Zaumseil, J.-F. Chang, E.C.-W. Ou, P.K.-H. Ho, H. Sirringhaus, R.H. Friend, Nature 434 (2005) 194–199. [52] H. Hoppe, D.A.M. Egbe, D. Mühlbacher, N.S. Sariciftci, J. Mater. Chem. 14 (2004) 3462–3467. [53] D.A.M. Egbe, L.H. Nguyen, D. Mühlbacher, H. Hoppe, K. Dchmidtke, N.S. Sariciftci, Thin Solid Films 511–512 (2006) 486–488. [54] A. Marrocchi, F. Silvestri, M. Seri, A. Facchetti, A. Taticchi, T.J. Marks, Chem. Commun. 11 (2009) 1380–1382. [55] R. Jadhav, S. Türk, F. Kühnlenz, V. Cimrova, S. Rathgeber, D.A.M. Egbe, H. Hoppe, Phys. Status Solidi A 206 (2009) 2695–2699. [56] D.A.M. Egbe, B. Carbonnier, E. Birckner, U.-W. Grummt, Polym. Sci. 34 (2009) 1023–1067. [57] S. Rathgeber, D. Bastos de Toledo, E. Birckner, H. Hoppe, D.A.M. Egbe, Macromolecules 43 (2010) 306–315. [58] F. Silvestri, A. Marrocchi, M. Seri, C. Kim, T.J. Marks, A. Facchetti, A. Taticchi, J. Am. Chem. Soc. 132 (2010) 6108–6123. [59] F. Silvestri, A. Marrocchi, Int. J. Mol. Sci. 11 (2010) 1471–1508. [60] M. Seri, A. Marrocchi, D. Bagnis, R. Ponce, A. Taticchi, T.J. Marks, A. Facchetti, Adv. Mater. 23 (2011) 3827–3831. [61] A. Marrocchi, I. Tomasi, L. Vaccaro, Isr. J. Chem. 52 (2012) 41–52. [62] A. Marrocchi, M. Seri, C. Kim, A. Facchetti, A. Taticchi, T.J. Marks, Chem. Mater. 21 (2009) 2592–2594.

27

[63] J.K. Kochi, G.S. Hammond, J. Am. Chem. Soc. 75 (1953) 3452–3458. [64] T. Yamamoto, W. Tamada, M. Takagi, K. Kizu, T. Maruyama, Macromolecules 27 (1994) 6620–6626. [65] S. Leroy-Lhez, M. Allain, J. Oberle, F. Fages, New J. Chem. 31 (2007) 1013–1021. [66] Q. Meng, J. Gao, R. Li, L. Jiang, C. Wang, H. Zhao, C. Liu, H. Li, W. Hu, J. Mater. Chem. 19 (2009) 1477–1482. [67] A. K. Diallo, F. Fages, F. Serein-Spirau, J.-P. Lère-porte, C. Videlot-Ackermann, Appl. Surf. Sci. 257 (2011) 9386–9389. [68] H. Wang, H.S. Lim, S. Kim, J. Lim, C. Lee, D.W. Kim, Synth. Met. 159 (2009) 2564–2570. [69] A.K. Diallo, C. Videlot-Ackermann, P. Marsal, H. Brisset, F. Fages, A. Kumagai, N. Yoshimoto, F. Serein-Spirau, J.-P. Lère-Porte, Phys. Chem. Chem. Phys. 12 (2010) 3845–3851. [70] A.J.J.M. van Breemen, P.T. Herwig, C.H.T. Chlon, J. Sweelssen, H.F.M. Schoo, S. Setayesh, W.M. Hardeman, J. Am. Chem. Soc. 128 (2006) 2336–2345. [71] T.K. An, S.-H. Hahn, S. Nama, H. Cha, Y. Rho, D.S. Chung, M. Ree, M.S. Kang, S.-K. Kwon, Y.-H. Kim, C.E. Park, Dyes Pigments 96 (2013) 756–762. [72] E. Birckner, U.-W. Grummt, A.H. Go1ller, T. Pautzsch, D.A.M. Egbe, M. Al-Higari, E. Klemm, J. Phys. Chem. A 105 (2001) 10307–10315. [73] T. Narita, M. Takase, T. Nishinaga, M. Iyoda, K. Kamada, K. Ohta, Chem. Eur. J. 16 (2010) 12108 –12113.

28

[74] S. Hachiya, K. Asai, G.-I. Konishi, Tetrahedron Lett. 54 (2013) 3317–3320. [75] V.K. Chaikovskii, V.I. Skorokhodov, V.D. Filimonov, Zh. Org. Khim. 37 (2001) 1503–1504. [76] D. Sahu, H. Padhy, D. Patra, D. Kekuda, C.-W. Chu, I.-H. Chiang, H.-C. Lin, Polymer 51 (2010) 6182–6192. [77] Q. Niu, Y. Lu, H. Sun, X. Li, X. Tao, Dyes Pigments 97 (2013) 184–197. [78] O. Lavastre, L. Ollivier, P.H. Dixneuf, Tetrahedron 52 (1996) 5495–5504. [79] A. Schoenberg, I. Bartoletti, R.F. Heck, J. Org. Chem. 39 (1974) 3318–3326. [80] J.B. Shi, B. Tong, W. Zhao, J.B. Shen, J.G. Zhi, Y.P. Dong, M. Hä1ussler, J.W.Y. Lam, B.Z. Tang, Macromolecules 40 (2007) 5612–5617. [81] G. Bordeau, R. Lartia, G. Metge, C. Fiorini-Debuisschert, F. Charra, M.P. Teulade-Fichou, J. Am. Chem. Soc. 130 (2008) 16836–16837. [82] S.M. Song, D. Ju, J.F. Li, D.X. Li, Y.L. Wei, C. Dong, P.H. Lin, S.M. Shuang, Talanta 77 (2009) 1707–1714. [83] B.J. Walker, A. Dorn, V. Bulovi, M.G. Bawendi, Nano Lett. 11 (2011) 2655–2659. [84] J. Luo, Z. Xie, J.W.Y. Lam, L. Cheng, H. Chen, C. Qiu, H.S. Kwok, X. Zhan, Y. Liu, D. Zhu, B.Z. Tang, Chem. Commun. 18 (2001) 1740–1741. [85] Z. Wang, H. Shao, J. Ye, L. Tang, P. Lu, J. Phys. Chem. B 109 (2005) 19627–19633. [86] W. Qin, D. Ding, J.Z. Liu, Z.Y. Wang, Y. Hu, B. Liu, B.Z. Tang, Adv. Funct. Mater. 22 (2012) 771−779. 29

[87] Y. Hong, et al. J. Am. Chem. Soc. 134 (2012) 1680−1689. [88] X.M. Hu, Q. Chen, J.X. Wang, Q.Y. Cheng, C.G. Yan,, J. Cao, Y.J. He, B.H. Han, Chem. Asian J. 6 (2011) 2376−2381. [89] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, et al. Gaussian 03, revision A. 1. Pittsburgh, PA: Gaussian, Inc.; 2004. [90] S.H. Zeng, L.H. Yin, X.Y. Jiang, Y.Q. Li, K. C. Li, Dyes and Pigments 95 (2012) 229–235. [91] Y. Li, X. Tao, F. Wang, T. He, M. Jiang, Org. Electron. 10 (2009) 910–917.

30

Figure captions: Fig. 1. The structures of dyes 2TBEA, 2TBDA and TEPEB. Scheme 1. Synthetic routes to 2TBEA, 2TBDA and TEPEB. Fig. 2. TGA results of three dyes with a heating rate of 10 °C/min under nitrogen. Fig. 3(a). Normalized UV–Vis absorption spectra of 2TBEA, 2TBDA and TEPEB in CHCl3 (C =1.0 × 10–5 M). Fig. 3(b). Normalized UV–Vis absorption spectra of 2TBEA, 2TBDA and TEPEB in CHCl3 with different concentrations (C =1.0 × 10–6 – 1.0 × 10–4 M). Table 1. Optical, electrochemical and DFT calculated characteristics of 2TBEA, 2TBDA and TEPEB. Fig. 4(a). Photoluminescence emission spectra of three dyes in CHCl3 (C = 5.0 × 10–6 M); Fig. 4(b). The fluorescence excitation and emission spectra of compound TEPEB in CHCl3 with the concentration of 5.0 × 10–6 M. (The excitation and emission slit widths were both 5 nm). Fig. 5. PL spectra of 2TBEA, 2TBDA and TEPEB in CHCl3 with different concentrations. Table 2. Fluorescence quantum yields of 2TBEA, 2TBDA and TEPEB in CHCl3 with different concentrations. Fig. 6. Optimized geometries of 2TBEA, 2TBDA and TEPEB. Atom coloring: white, hydrogen; gray, carbon; yellow, sulfur; green, silicon; blue, nitrogen. Isosurface cut-off value: 0.02. Fig. 7. The frontier molecular orbitals of 2TBEA, 2TBDA and TEPEB calculated 31

with TD-DFT on B3LYP/6-31G*. Fig. 8. CV curves measured in CH2Cl2 of 2TBEA, 2TBDA and TEPEB. Fig. 9. XRD in reflection mode for the powder samples of three dyes. Table 3. XRD data of 2TBEA, 2TBDA and TEPEB. Fig. 10. OM images of 2TBEA, 2TBDA and TEPEB. Fig. 11. SEM images of 2TBEA (a), 2TBDA (b) and TEPEB (c). The microribbons were obtained by 1 mg/mL chloroform solution precipitated on the Si/SiO2 substrate. Fig. 12. AFM images of 2TBEA (a), 2TBDA (b) and TEPEB (c) were obtained by 1 mg/mL chloroform solution on the Si/SiO2 substrate.

32

Fig. 1.

Scheme 1. S

S

I Pd(PPh3)2Cl2-CuI-PPh3

S

+ H2N

S

H2N

Et3N, THF, 50 oC

1

2TBEA

NH2 S S

+ H2N

H2N

I Pd(PPh3)2Cl2-CuI-PPh3 Et3N, THF, 50 oC

1

S S

H2N

2TBDA

Pd(PPh3)2Cl2-CuI-PPh3 + Me3Si 2

I Et3N, THF, 50 oC 3 Me3Si

SiMe3 TEPEB

33

Fig. 2. 105 o

100

78 C 5% weight loss

95

o

183 C

90 85 37% weight loss

80 75

2TBEA

70 65 o

790 C

60 100

105

200

300

400

500

600

700

800

900

o

117 C

100 5% weight loss

95

o

Weight ( %)

209 C

90 85 37% weight loss

80

2TBDA

75 70 65 o

793 C

60 200

400 600 o Temperature ( C)

800

o

100

95 C 5% weight loss o

147 C

Weight ( %)

80

60

91% weight loss

40

20

TEPEB o

791 C

0 100

200

300

400 500 600 o Temperature ( C)

700

34

800

Fig. 3(a). 1.0

TEPEB 2TBDA 2TBEA

Abs / a.u.

0.8 0.6 0.4 0.2 0.0 -0.2 200

300

400 Wavelength / nm

500

Table 1.

35

600

Fig. 3(b) 1.0

2TBEA

-6

1*10 -5 1*10 -4 1*10

Abs / a.u.

0.8 0.6 0.4 0.2 0.0 300

1.0

400 Wavelength / nm

500

600

-6

1*10 -5 1*10 -4 1*10

2TBDA

Abs / a.u.

0.8 0.6 0.4 0.2 0.0 -0.2 200

1.0

300

400 Wavelength / nm

500

TEPEB

-6

1*10 -5 1*10 -4 1*10

0.8

Abs / a.u.

600

0.6 0.4 0.2 0.0 200

300 400 Wavelength / nm

500

36

Fig. 4(a) 10000

2TBEA 2TBDA TEPEB

Intensity / a.u.

8000

6000

4000

2000

0 350

400

450

500

550

600

650

Wavelength / nm

Fig. 4(b) 3500

Emission Excitation

Fluorescence intensity / a.u.

3000 2500 2000 1500 1000 500 0

200

300

400 Wavelength / nm

500

37

600

Fig. 5 10000

2TBEA

Intensity / a.u.

8000

−4

5× 10 −4 1× 10 −5 5× 10 −5 1× 10 −6 5× 10 −6 1× 10 −7 5× 10 −7 1× 10 −8 5× 10 −8 1× 10

6000

4000

2000

0 400

450

500

550

600

650

700

Wavelenghth / nm

Intensity / a.u.

10000

2TBDA

−4

5× 10 −4 −4 1× 10 −5 5× 10 −5 1× 10 −6 5× 10 −6 1× 10 −7 5× 10 −7 1× 10 −8 5× 10 −8 1× 10

8000 6000 4000 2000 0 350

400

450

500

550

600

650

700

Wavelength / nm

TEPEB

3500

−4

5× 10 −4 1× 10 −5 5× 10 −5 1× 10 −6 5× 10 −6 1× 10 −7 5× 10 −7 1× 10 −8 5× 10 −8 1× 10

Intensity / a.u.

3000 2500 2000 1500 1000 500 0 350

400

450

Wavelength / nm

38

500

Table 2. Compound

Φa1

Φa2

Φa3

Φa4

Φa5

Φa6

Φa7

Φa8

Φa9

Φa10

2TBEA

0.21

0.33

0.42

0.47

0.70

0.64

0.53

0.45

0.36

0.23

2TBDA

0.21

0.26

0.43

0.49

0.59

0.75

0.61

0.51

0.35

0.24

TEPEB

0.09

0.14

0.19

0.26

0.32

0.37

0.51

0.35

0.32

0.27

1-10 a

was represent for the concentration from 1.0 × 10–8 to 5.0 × 10–4 M.

The fluorescence quantum yields (Φ) were measured in CHCl3 using quinine sulfate

(Φ = 0.55) as standard.

Fig. 6 2TBEA

2TBDA

TEPEB

39

Fig. 7

HOMO–1

HOMO

LUMO

LUMO+1

2TBEA

2TBDA

40

TEPEB

Fig. 8 0.00002

2TBEA

Current (A)

0.00000

-0.00002

-0.00004

-0.00006

-1

0 + Potentail (V vs Fc )

Current (A)

0.000050

1

2

2TBDA

0.000025 0.000000 -0.000025 -0.000050

-1

0

1

2

+

Potentail (V vs Fc )

0.00010

TEPEB Current (A)

0.00005

0.00000 onset

-0.00005

-2

-1

0

1 +

Potentail (V vs Fc )

41

2

Fig. 9 1200

Intensity / a.u.

1000

TEPEB 800 34 5

1 2

7

6

8

600

2TBEA 400

23 4

1

200 1 2

5

6

7

2TBDA

3 4

5

6

0 10

20

30

40

2θ /

50

60

o

Table 3. XRD 2θ /

Compound

o

d/Ǻ

2TBEA

17.01, 19.75,

20.50,

22.00,

28.12, 37.96, 48.64

5.21,

4.49,

4.33, 4.04, 3.17,

2.37,

2TBDA

16.34, 18.26,

20.25,

22.66,

28.90, 36.76

5.42,

4.86,

4.38, 3.92, 3.09,

2.44

TEPEB

14.45, 16.95,

24.26,

25.59,

29.20, 34.36, 43.34,

6.13,

5.23,

3.67, 3.48, 3.06,

2.61,

52.65

Fig. 10

500 µm

2TBEA

500 µm

2TBDA

42

500 µm

TEPEB

1.87

2.09, 1.74

Fig. 11 (a)

(b)

(c)

43

Fig. 12 (a)

(b)

(c)

44

Graphical Abstract

10000

H2N

2TBEA

NH2 S H2N

S 2TBDA

Me3Si

Fluorescence intensity / a.u.

S S

2TBEA 2TBDA TEPEB

8000

6000

4000

2000

SiMe3

0 350

400

450

500

550

Wavelength / nm

TEPEB

45

600

650

Highlights ► Three novel fluorescent molecules with carbon–carbon triple bonds 2TBEA, 2TBDA and TEPEB were designed and synthesized. ► Their optical and electrochemical properties were investigated. ► thin-film materials

46

Synthesis, photophysical and thin-film self-assembly properties of novel fluorescent molecules with carbon-carbon triple bonds.

Three novel fluorescent molecules with carbon-carbon triple bonds 2TBEA, 2TBDA and TEPEB are successfully designed and synthesized. Their thermal, pho...
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