FULL PAPER DOI: 10.1002/asia.201402768

Arylacetylene-Substituted Naphthalene Diimides with Dual Functions: Optical Waveguides and n-Type Semiconductors Yonghai Li, Guanxin Zhang,* Wei Zhang, Jianguo Wang, Xin Chen, Zitong Liu, Yongli Yan, Yongsheng Zhao, and Deqing Zhang*[a] Abstract: New arylacetylene-substituted naphthalene diimides (NDIs) 1–6, with both light-emitting and semiconducting functions, are reported. Among them, the crystal structure of 1 was determined. On the basis of their reduction potentials and thin-film absorption spectra, the HOMO/LUMO energies of these modified NDIs were estimated. The results reveal that their HOMO/LUMO energies are slightly affected by the flanking aryl groups. The emission colors of these NDIs vary from green to red, and interestingly,

they show aggregation-induced emission enhancement behavior with fluorescence quantum yields reaching 9.86 % in the solid state. Microrods of 1, 3, and 5 show typical optical waveguiding behavior with relatively low optical-loss coefficients. Organic fieldeffect transistors with thin films of these NDIs were fabricated with conKeywords: naphthalene diimide · arylacetylene · optical waveguide · organic semiconductors

Introduction

bithiophene conjugated polymers that had n-type semiconducting properties with electron mobilities of up to 0.85 cm2 V1 s1.[22] Gao and co-workers synthesized a series of NDI derivatives that contained 2-(1,3-dithiol-2-ylidene)malonitrile groups (electron withdrawing); electron mobilities as high as 3.50 cm2 V1 s1 in air were reported for thin films of some of these NDI derivatives after optimization of the alkyl chains.[23] Wrthner et al. reported p-type and ambipolar semiconductors based on core-expanded NDIs.[24] Some of us recently described NDI derivatives containing electron-donating tetrathiafulvalene or 1,3-dithole-2-thioneACHTUNGRE(-one) moieties, and they behaved as either n- or p-type or ambipolar materials, depending on the substitution groups.[25] NDI can be also modified at the shoulder positions (Scheme 1). We recently described the transformation of NDI into a more expanded conjugated framework that involved arylacetylene-substituted NDI.[26] Incorporation of functional groups into the NDI core was widely realized through CC single bonds, but the usage of rigid ethynylene (CC) bonds was seldom reported.[27] Herein, we report the synthesis and physical studies of arylacetylene-substituted NDIs 1–6 (Scheme 2). The results reveal that these NDI derivatives show aggregation-induced emission enhancement (AIEE) behavior; they are weakly emissive in solutions, but their emission intensities are enhanced after aggregation. The emission colors can be finely tuned by varying the aryl groups and, among them, microrods of 1, 3, and 5 can function as optical waveguides. Moreover, the LUMO energies of these new NDI derivatives can be tuned again

1,4,5,8-Naphthalene diimide (NDI) and its derivatives have been intensively investigated for organic semiconductors and photovoltaic materials.[1–10] To enhance the performances of NDI-based materials, various chemical modifications of the NDI framework were carried out. Chemical modifications of the NDIs can be mainly achieved in two different ways. One is to introduce substituents at the head positions of the imide groups and the other is to incorporate functional moieties at the core positions of NDI (Scheme 1). However, only substitution at the core positions will have a significant effect on the optical and HOMO/LUMO levels, especially modification with electron acceptors and/or donors.[11–14] By following this strategy, a number of NDI derivatives were designed and synthesized for the development of high-performance optoelectronic materials.[15–21] For instance, Facchetti and co-workers reported alternating NDI–

[a] Y. Li, Dr. G. Zhang, W. Zhang, J. Wang, X. Chen, Dr. Z. Liu, Dr. Y. Yan, Prof. Y. Zhao, Prof. D. Zhang Beijing National Laboratory for Molecular Sciences Organic Solids Laboratory and Photochemistry Laboratory Institute of Chemistry, Chinese Academy of Sciences Beijing 100190 (P.R. China) Fax: (+ 86) 10-62562693 E-mail: [email protected] [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201402768.

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ventional techniques. The results indicate that thin films of 2, 4, and 6, with long and branched alkyl chains, show air-stable n-type semiconducting properties with electron mobilities of up to 0.035 cm2 V1 s1 after thermal annealing, whereas 1, 3, and 5, with short alkyl chains, behave as n-type semiconductors under a nitrogen atmosphere with electron mobilities of up to 0.075 cm2 V1 s1 after thermal annealing.

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Scheme 1. Chemical modifications of NDIs (F.G. = functional group).

Scheme 2. The chemical structures of and synthetic approach to arylacetylene-substituted NDIs 1–6. i) Corresponding tin reagents, [PdACHTUNGRE(PPh3)4], toluene, reflux, 2.0 h, yields: 80–90 %. (C6H13 = n-hexanyl; C20H41 = 2-octyldodecyl)

ties were confirmed by elemental analysis. Thermogravimetric analysis (TGA), as shown in Figure S1 and Table S1 in the Supporting Information, indicates that the decomposition temperatures of these new NDI derivatives, defined as the temperature at which there is an initial 5 % weight loss in the respective TGA curves, are higher than 300 8C under a nitrogen atmosphere. Thus, they are thermally stable. Single crystals of 1 suitable for X-ray analysis were obtained and its crystal structure was successfully determined. Figure 1 shows the molecular structure, dihedral angle between pyridine rings and the NDI core, and intermolecular arrangement of 1. As shown in Figure 1, the molecular struc-

by varying the aryl groups. Among them, compounds 2, 4, and 6 behave as air-stable n-type semiconductors with electron mobilities of up to 0.035 cm2 V1 s1.

Results and Discussion Synthesis and Crystal Structure

Figure 1. Molecular structure (a), dihedral angle between the pyridine rings and the NDI core (b), and the intermolecular arrangement (c) of compound 1.

Arylacetylene-substituted NDIs were synthesized by a Stille coupling reaction between dibromonaphthalenediimide (2BrNDI)[28] and the respective tin reagents (see Scheme 2). The tin reagents were prepared from the corresponding arylacetylene and used without strict purification (see the Supporting Information). Their structures were characterized by NMR spectroscopy and mass spectrometry, and their puri-

ture of 1 is centrosymmetrical. The pyridine rings are not coplanar with the central NDI core, and form a dihedral angle of 37.798. As depicted in Figure S2a and S2b in the Supporting Information, the intermolecular separation between neighboring NDI cores is 3.378 , and that between neighboring pyridine rings is 3.344 ; however, the two neighboring NDI cores and neighboring pyridine rings are displaced from each other, as shown in Figure S2c in the Supporting Information. Short interatomic contacts (2.436  for O···H’ and 2.696  for N···H’) exist within the crystal of 1 (see Figure S3 in the Supporting Information). The short intermolecular interactions will fix the molecular conformations of 1 in the solid state; thus inhibiting internal rotations and blocking their nonradiative relaxation, according to previous studies.[29] This result agrees well with the observation that 1 shows relatively strong emissions in the solid state (see below). Unfortunately, single crystals of other NDI derivatives suitable for crystal-structure analysis were not obtained.

Abstract in Chinese:

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As depicted in Figure 2, the thin-film absorption spectra of these NDI derivatives are further redshifted to different extents, in comparison with the corresponding absorptions in solutions. According to previous reports, such absorption spectral redshifts may result from intermolecular interactions within the thin films, which may involve electrondonor and -acceptor interactions.[26] Moreover, the NDIs with C6H13 alkyl chains exhibit larger redshifts than those with C20H41. For instance, a thin film of 4, with C20H41 alkyl chains, absorbs at l = 505 and 543 nm, whereas 5, with C6H13, shows absorptions at l = 582 and 610 nm (Table 1). This may be explained by considering the fact that bulky  C20H41 chains (compared with C6H13) may inhibit intermolecular p–p interactions, and thus, the absorption spectra of thin films of 4, with C20H41 alkyl chains, are only slightly redshifted. On the basis of the onset absorptions of the thin films, optical band gaps of these NDIs were determined (see Table 2) and narrower band gaps were observed for NDIs with electron-donating groups.

Absorption Spectra and HOMO/LUMO Energies Figure 2 shows the absorption spectra of 1–6 in solution and as thin films. They mainly show two absorption bands: one

Table 2. Reduction potentials and HOMO/LUMO energies of 1–6.

1 2 3 4 5 6

Figure 2. a) The absorption spectra of solutions of 1, 3, and 5 and their thin films. b) The absorption spectra of solutions of 2, 4, and 6 and their thin films; the concentration of each solution was 1.0  105 m in CH2Cl2.

E1/2red1 [V]

E1/2red2 [V]

Eonsetred1 [V]

LUMO [eV]

HOMO [eV]

Egopt [eV]

0.39 0.50 0.50 0.51 0.51 0.54

0.86 0.91 0.91 0.93 0.93 0.97

0.34 0.44 0.44 0.43 0.43 0.47

4.07 3.97 3.97 3.98 3.98 3.94

6.49 6.28 6.13 6.07 5.92 6.02

2.42 2.31 2.16 2.09 1.94 2.08

Two reversible reduction potentials were detected for 1–6, as shown in Figure 3. Clearly, the reduction potentials were negatively shifted after incorporation of electron-donating groups. Compound 1 exhibits Ered11/2 = 0.39 V and Ered21/2 = 0.86 V, whereas those of compound 6 are shifted to 0.54 and 0.97 V, respectively. On the basis of the respective onset reduction potentials, LUMO energies were estimated by using the equation LUMO = (Eonsetred1 + 4.41) eV.[30] As listed in Table 2, the LUMO energies increase in the following order: 1 < 2 = 3  4 = 5 < 6. In combination with the optical Table 1. The absorption and fluorescence data of arylacetylene-substituted NDIs 1–6. band gaps, the HOMO energies of 1–6 were estimated by using Absorption[a] Emission Solution Thin film Solution Solid state the equation HOMO = lmax[b] [nm] lmax[b] [nm] lem[c] [nm] F[d] [%] lem [nm] F[e] [%] < t > [f] [ns] (EggapLUMO) (see Table 2). in the range of l = 275 to 400 nm and another from l = 400 to 650 nm. It is clear that the absorptions are affected by the flanking aryl groups and the absorption maxima are redshifted by increasing the electron-donating abilities of the aryl groups. For instance, relative to the absorptions of 6 at l = 530 nm and 4 at l = 525 nm in solution, those of 1 and 3 are hypsochromically shifted to l = 450 and 490 nm, respectively (Table 1).

1 2 3 4 5 6

450 490 490 525 525 530

475 507 523 505,543 582,610 520,551

500 520 520 564 564 598

0.7 0.8 0.5 0.6 0.6 0.8

541 550 610 630 708 642

5.70 1.80 9.86 3.20 4.64 4.55

5

3.63 1.34 11.28 2.16 7.98 1.39

[a] The absorption spectra were measured in CH2Cl2 (1.0  10 m). [b] Lowest-energy absorption maxima. [c] The fluorescence spectra were measured in CH2Cl2 (1.0  105 m). [d] The solution quantum yields were measured by using rhodamine 101 (F = 100 % in ethanol) as a standard. [e] The quantum yields in the solid states were measured by using the absolute integrating sphere method. [f] The apparent decay time constant n n P P < t > (average fluorescence lifetime) was determined by using the relationship hti ¼ ai ti = ai (n = 1–2), in i¼1 i¼1 which ti and ai represent the individual exponential decay time constant and the corresponding pre-exponential factor, respectively.

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AIEE and Optical WaveGuiding Properties These arylacetylene-substituted NDIs are weakly emissive in solution with quantum yields lower than 1 % (see Table 1). As expected, the emission maxima of these NDIs can be tuned by the flanking aryl

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with C6H13 alkyl chains) may weaken the intermolecular interactions and, as a result, the internal rotations cannot be inhibited fully for these NDIs with C20H41 alkyl chains even in the solid state. It is interesting to note that microrods of 1, 3, and 5 exhibit optical wave-guiding behavior. Figure 4 a, e, and i shows the photoluminescence (PL) images of microrods of 1, 3, and 5, respectively. The microrods of both 1 and 3 exhibit bright luminescence spots at the respective two rod ends and relatively weaker emission from the rod bodies. Interestingly, all of the microrods of 5 exhibit bright luminescence spots at only one of the rod ends. These three microrods were excited with a focused laser down to the diffraction limit at different local positions along the microrods. As shown in Figure 4 b and f, yellow– green and orange emissions were observed from both ends of the microrods of 1 and 3, respectively, irrespective of the excitation position. Generally, the emission of light can only be observed at the local area of the excited position. The appearance of the out-coupling light at the ends of each microrod is a characteristic of typical waveguide behavior. Thus, microrods of 1 and 3 can function as active waveguides. Being different from microrods of 1 and 3, those of 5 exhibit red emission at only one end. Microrods of 5 are potentially useful for unidirectional transmission of light. To gain further insight into the wave-guiding behavior within the microrods of 1, 3, and 5, their spatially resolved PL spectra were measured. Figure 4 c shows the collected PL spectra at the end of a single microrod of 1 under excitation at different positions (labeled as 1, 2, 3, 4, 5 and 6). Clearly, the emission intensity at the microrod ends decreases upon increasing the propagation distance. As depicted in Figure 4 d, the emission intensity at l = 554 nm of the outcoupled light decreases almost exponentially with the propagation distance. By fitting the data of Figure 4 d, according to the reported procedure,[33] the optical loss coefficient at l = 554 nm for microrods of 1 was estimated to be 28.8 dB mm1. Similarly, the PL spectra at the end of a single microrod of 3 and 5 were measured (see Figure 4 g and k). By fitting the respective variation of emission intensity versus the propagation distance shown in Figure 4 h and l, the optical loss coefficients for microrods of 3 and 5 were estimated to be 5.70 and 16.4 dB mm1, respectively. On the basis of the optical-loss coefficients, microrods of 3 and 5 can transport light more efficiently than those of 1.

Figure 3. Cyclic voltammograms of 1–6 in CH2Cl2 (1.0  103 m) at a scan rate of 100 mV s1, obtained by using a glassy carbon working electrode, a Pt counter electrode, Ag/AgCl (saturated KCl) as the reference electrode, and nBu4NPF6 (0.1 m) as a supporting electrolyte.

groups with different electron-donating abilities, as shown in Figure S4 in the Supporting Information, in which the fluorescence spectra of these NDIs in solution are displayed. The emission maxima are redshifted in the following order: 1 < 2 = 3 < 4 = 5 < 6. However, the fluorescence intensities of these NDIs can be enhanced after aggregation. For instance, a solution of 3 in CH2Cl2 is weakly emissive, but the fluorescence intensity is gradually enhanced after the addition of n-hexane and the emission maximum is simultaneously blueshifted, as depicted in Figure S5 in the Supporting Information.[31] The fluorescence intensity at l = 520 nm increases by 20 times when the volume fraction of n-hexane reaches 99 % in solution. As shown in Figure S5 in the Supporting Information, such fluorescence intensity enhancements and blueshifts of the emission maxima were also observed for other NDIs. Therefore, it can be concluded that these arylacetylene–NDIs show AIEE behavior.[32] Such unusual fluorescent behavior of these NDIs may be understood as follows: 1) internal rotations of aryl groups and alkyl chains may lead to the weak emission of these NDIs in solution; and 2) internal rotations will be inhibited largely after aggregation. As a result, the emission intensities are enhanced after aggregation. The emission spectra, quantum yields, and fluorescence lifetimes were also measured for crystalline samples of these NDIs, as shown in Table 1 and Figure S6 in the Supporting Information. Clearly, the emission quantum yields of these NDIs in the solid state are higher than those of the respective solutions. Among them, compound 3 is strongly emissive with a quantum yield of up to 9.86 % in the solid state. In the crystalline state, intermolecular interactions would further inhibit internal rotations within these NDIs, and consequently, they become more emissive. Compared with the fluorescent spectra in solution, the emission spectra of these NDIs are further redshifted in the solid state, as shown in Figure S4 in the Supporting Information. The emission maxima in the solid state are redshifted in the following order: 1 < 3 < 5 and 2 < 4 < 6. Notably, NDIs with C6H13 alkyl chains possess relatively higher quantum yields and larger redshifts than those with C20H41 alkyl chains. This is probably because the bulky C20H41 alkyl chains (compared

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Thin-Film Organic Field-Effect Transistors (OFETs) The semiconducting behavior of these arylacetylene-substituted NDIs were investigated by characterizing OFETs with their thin films. Bottom-gate bottom-contact OFETs of these NDIs were fabricated with conventional techniques (see the Experimental Section). Based on the respective transfer and output characteristics (see Figure 5 and Figure S7 in the Supporting Information), thin films of these arylacetylene-substituted NDIs exhibit n-type OFET behavior.

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Figure 4. PL images of the 1D microrods of 1 (a), 3 (e), and 5 (i) excited with a mercury lamp. PL images obtained by exciting an identical microrod at different positions of microrods of 1 (b), 3 (f), and 5 (j). The spatially resolved spectra of the emissions that are out-coupled at the tip of microrods of 1 (c), 3 (g), and 5 (k). The output intensity as a function of propagation length for 1 (d), 3 (h), and 5 (l) is also shown.

Figure 5. Typical output and transfer characteristics of OFETs with thin films of 4 and 5; the channel width (W) was 1440 mm for all OFETs devices, and the lengths (L) were 50 and 40 mm for those with thin films of 4 and 5, respectively. OFETs with thin film of 4 were measured in air, while those with thin films of 5 were measured under nitrogen atmosphere.

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This agrees well with their relatively low LUMO energies (see Table 2). Thin films of 2, 4, and 6 showed air-stable n-type semiconducting behavior. The electron mobilities of as-prepared thin films of 2, 4, and 6 were in the range of 7.5  106–3.8  105 cm2 V1 s1. However, their electron mobilities increased after thermal annealing, as listed in Table 3. For instance, the electron mobility of a thin film of 4 increased from 5.4  105 to 0.035 cm2 V1 s1 after thermal annealing at 100 8C. Further annealing at 120 8C led to a decrease in electron mobility (see Table 3). In comparison, thin films of 1, 3, and 5 show air-unstable ntype semiconducting properties. Such a difference between 2/4/6 and 1/3/5 may be explained as follows: long alkyl chains may

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Table 3. The electron mobilities [max. (avg.)], threshold voltages (VTh) [min. (avg.)], and current on/off ratios for bottom-gate bottom-contact OFET devices based on thin films of 1–6 after thermal annealing at different temperatures. The data were based on at least 10 devices.

1

2

3

4

5

6

me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff) me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff) me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff) me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff) me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff) me [cm2 Vs1] VTh [V] logACHTUNGRE(Ion/Ioff)

25 8C

80 8C

100 8C

120 8C

1.3  104 (1.0  104) 25 (30) 4–6 7.5  106 (6.8  106) 34 (39) 4–5 3.5  105 (3.0  105) 37 (40) 4–5 5.4  105 (4.4  105) 42 (45) 4–5 7.0  104 (5.5  104) 36 (40) 4–5 3.8  105 (3.4  105) 35 (38) 4–5

0.017 (0.014) 14 (19) 5–6 0.002 (0.001) 28 (32) 4–5 0.005 (0.003) 33 (36) 5–6 0.007 (0.005) 25 (31) 5–6 0.022 (0.019) 28 (33) 4–6 0.010 (0.008) 30 (33) 5–6

0.011 (0.009) 15 (19) 5–6 0.008 (0.006) 22 (28) 5–6 0.012 (0.009) 28 (30) 5–6 0.035 (0.029) 7.5 (13) 6–7 0.075 (0.051) 21 (29) 5–7 0.016 (0.012) 23 (27) 5–7

0.005 (0.004) 18 (22) 5–6 0.004 (0.003) 20 (24) 5–6 0.009 (0.006) 25 (31) 5–6 0.019 (0.014) 18 (24) 5–7 0.031 (0.025) 31 (35) 5–7 0.008 (0.006) 25 (28) 5–7

be beneficial for excluding oxygen and water molecules, which will otherwise reduce the stability of the respective anions in air. For this reason, the transfer and output characteristics of OEFTs with 1, 3, and 5 were measured under a nitrogen atmosphere. As listed in Table 3, the electron mobilities of the as-prepared thin films were rather low, but they increased greatly after thermal annealing. For instance, electron mobility for a thin film of 5 increased from 7.0  104 to 0.075 cm2 V1 s1 after thermal annealing at 100 8C. Again, the electron mobilities of 1, 3, and 5 started to decrease by increasing the annealing temperature to 120 8C. The electron mobilities, threshold voltages (Vth), and current on/off ratio of devices based on 1–6 after thermal annealing at different temperatures are listed in Table 3. To understand the variation in the electron mobilities of these modified NDIs after thermal annealing, their thin films were characterized by AFM and XRD. As examples, Figure 6 shows the respective AFM images and XRD patterns of as-prepared thin films of 4 and 5 and those after annealing. Only one weak diffraction peak at 2q = 4.308 was detected for the as-prepared thin film of 4, but additional signals emerged after thermal annealing, as depicted in Figure 6. The second- (at 2q = 8.648), third- (at 2q = 12.978), and even fourth-order (at 2q = 17.228) diffraction signals were observed for the thin film of 4; the corresponding d spacing was estimated to be 20.5 . Thus, intermolecular lamellar packing exists in the thin film of 4 after thermal annealing. This is probably due to the interdigitated arrangements of alkyl chains, as illustrated in Figure 6 b. It is clear that the thin-film crystallinity of 4 is improved upon thermal annealing at 100 8C. For the thin film of 5, apart from the diffraction signal at 2q = 5.318, an additional weak diffraction peak at 2q = 15.908 was detected after thermal annealing at 100 and 120 8C. Similarly, the d spacing was estimated to be 16.6 , which was shorter than that for 4. This is consistent with the lengths of the alkyl chains within 4 and 5.

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These XRD data agree with the observation that electron mobilities of these modified NDIs increase upon thermal annealing (see Table 3). The thin-film morphologies were also altered after thermal annealing. For instance, the sizes of the molecular domains increased to about 250–350 nm after thermal annealing at 100 8C for a thin film of 4. The formation of interconnected microplatets was observed for the thin film of 5 after thermal annealing at 100 8C (see Figure 6 f). Such thin-film morphology is beneficial for carrier transport, according to previous reports.[34]

Figure 6. XRD patterns of thin films of 4 (a) and 5 (d) after annealing at different temperatures. Illustration of the intermolecular arrangements of 4 (b) and 5 (e). AFM images of thin films of 4 (c) and 5 (f) before and after annealing at 100 8C.

Conclusion Six arylacetylene-substituted NDIs were synthesized and characterized. On the basis of the crystal structure of 1, the flanking aryl groups were not coplanar with the NDI core. Both HOMO/LUMO and absorption/fluorescence spectra of these modified NDIs can be slightly tuned by the flanking aryl groups. Interestingly, these NDIs were weakly emissive in solution, but their emission intensities were enhanced after aggregation; thus, they exhibited AIEE behavior. Moreover, the emission colors could be tuned from green (for 1) to red (for 5 and 6). Microrods of 1, 3, and 5 showed typical optical wave-guiding behavior with relatively low optical-loss coefficients. Furthermore, thin films of these NDIs exhibited n-type semiconducting properties based on characterization of the respective OFETs. The electron mobilities of 4 and 5 could reach 0.035 and 0.075 cm2 V1 s1, respec-

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tively, after thermal annealing. Notably, compounds 2, 4, and 6, with C20H41 alkyl chains, behaved as air-stable ntype semiconductors, whereas 1, 3, and 5, with C6H13 alkyl chains, exhibited stable n-type semiconducting properties under a nitrogen atmosphere. Therefore, these arylacetylene-substituted NDIs had dual (light emitting and semiconducting) functions. New arylacetylene-substituted NDIs will be explored to improve the light-emitting quantum yields and electron mobilities.

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determined under ambient conditions by using a Keithley 4200 SCS semiconductor parameter analyzer. General Procedure for the Preparation of Arylacetylene-Substituted NDIs A solution of 2BrNDI (N-C20H41, N-C6H13 ; 1.0 equiv), the corresponding tin reagent (3.0 equiv crude) and a catalytic amount of [PdACHTUNGRE(PPh3)4] in toluene (30 mL) was heated at reflux for 2.5 h under nitrogen atmosphere. After the reaction, the solvent was evaporated under vacuum and the residue was subjected to column chromatography on silica gel with petroleum ether (60–90 8C)/CH2Cl2 (v/v, 1/1) as the eluent. Arylacetylene-substituted NDIs were obtained in high yields. Compounds 2 and 4 were synthesized according to a previously reported procedure.[26a]

Experimental Section

Compound 1 Red solid; 81 % yield; 1H NMR (400 MHz, CDCl2CDCl2): d = 8.87 (s, 2 H), 8.72 (d, J = 4.3 Hz, 4 H), 7.62 (d, J = 5.1 Hz, 4 H), 4.29–4.12 (m, 4 H), 1.76 (dd, J = 14.7, 7.6 Hz, 4 H), 1.40 (dt, J = 16.3, 9.9 Hz, 12 H), 0.92 ppm (t, J = 6.9 Hz, 6 H); 13C NMR (101 MHz, CDCl2CDCl2): d = 161.7, 161.1, 150.0, 137.1, 130.4, 126.7, 126.4, 126.1, 126.1, 125.4, 98.8, 92.6, 41.3, 31.6, 28.0, 26.8, 22.7, 14.3 ppm; MS (MALDI-TOF): m/z: 637.3 [M+1] + ; elemental analysis calcd (%) for C40H36N4O4 : C 75.45, H 5.70, N 8.80; found: C 75.42, H 5.65, N 8.80.

Materials and Characterization Techniques Chemicals were purchased from Alfa Aesar and Sigma–Aldrich, and used as received without further purification. All solvents were purified and dried by following standard procedures, unless otherwise stated. 2BrNDI was synthesized according to previous reports.[28] The tin reagents used in Stille coupling were synthesized from the corresponding arylacetylene and used for the next step without further purification (see the Supporting Information).

Compound 3

1

H and 13C NMR spectra were determined by using tetramethylsilane (TMS) as an internal standard at 298 K. Mass spectra were measured in the MALDI-TOF mode. Elemental analysis was performed on a standard elemental analyzer. TGA-DTA (differential thermal analysis) measurements were carried out on a SHIMADZU DTG-60 instrument under a flow of dry nitrogen, with heating from room temperature to 550 8C at a heating rate of 10 8C min1. Cyclic voltammetric measurements were carried out in a conventional three-electrode cell by using a glassy carbon working electrode, a Pt counter electrode, and a Ag/AgCl (saturated KCl) reference electrode on a computer-controlled CHI660C instrument at room temperature; the scan rate was 100 mV s1, and nBu4NPF6 (0.1 m) was used as the supporting electrolyte.

Red solid; 90 % yield; 1H NMR (400 MHz, CDCl3): d = 8.86 (s, 2 H), 7.77 (d, J = 3.6 Hz, 4 H), 7.45 (d, J = 2.2 Hz, 6 H), 4.27–4.17 (m, 4 H), 1.77 (d, J = 7.0 Hz, 4 H), 1.42 (d, J = 37.5 Hz, 12 H), 0.91 ppm (t, J = 6.7 Hz, 6 H); 13 C NMR (101 MHz, CDCl3): d = 162.1, 161.7, 137.4, 132.8, 130.0, 128.8, 127.3, 126.6, 125.5, 125.3, 122.6, 103.1, 89.6, 41.2, 31.7, 28.1, 26.9, 22.7, 14.2 ppm; MS (MALDI-TOF): m/z: 635.3 [M+1] + ; elemental analysis calcd (%) for C42H38N2O4 : C 79.47, H 6.03, N 4.41; found: C 79.42, H 6.01, N 4.41. Compound 5 Red solid; 85 % yield; 1H NMR (400 MHz, CDCl3): d = 8.80 (s, 2 H), 7.65–7.54 (m, 2 H), 7.50 (d, J = 5.1 Hz, 2 H), 7.19–7.07 (m, 2 H), 4.28–4.14 (m, 4 H), 1.84–1.69 (m, 4 H), 1.49–1.26 (m, 12 H), 0.91 ppm (t, J = 6.8 Hz, 6 H); 13C NMR (101 MHz, CDCl3): d = 162.1, 161.6, 136.9, 134.9, 130.6, 127.9, 126.8, 126.5, 125.3, 124.9, 122.6, 96.64, 94.1, 77.5, 77.4, 77.2, 76.8, 41.2, 31.7, 28.1, 26.9, 22.7, 14.2 ppm; MS (MALDI-TOF): m/z: 647.3 [M+1] + ; elemental analysis calcd (%) for C38H34N2O4S2 : C 70.56, H 5.30, N 4.33, S 9.91; found: C 70.52, H 5.29, N 4.33, S 9.77.

Crystal-Structure Analysis Single crystals of 1 were grown by slow evaporation from a solution of 1 in toluene. The diffraction data were collected on a Rigaku Saturn diffractometer with a charge couple device (CCD) area detector. All calculations were performed by using the SHELXL97 and crystal-structure crystallographic software packages. CCDC 983738 (1) contains 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.

Compound 6 Red solid; 89 % yield; 1H NMR (400 MHz, CDCl3): d = 8.74–8.61 (m, 2 H), 8.38 (s, 2 H), 7.87 (dd, J = 4.4, 2.6 Hz, 2 H), 7.84–7.75 (m, 2 H), 7.53– 7.34 (m, 4 H), 4.19 (d, J = 6.8 Hz, 4 H), 2.04 (s, 2 H), 1.52–1.19 (m, 64 H), 0.84 ppm (q, J = 6.7 Hz, 12 H); 13C NMR (101 MHz, CDCl3): d = 162.4, 161.7, 139.3, 138.7, 136.9, 133.8, 126.7, 126.3, 125.6, 125.4, 124.9, 124.8, 123.8, 122.7, 118.3, 96.4, 93.0, 45.0, 37.0, 32.1, 32.0, 30.3, 29.9, 29.9, 29.8, 29.52, 29.50, 26.7, 22.8, 14.3 ppm; MS (MALDI-TOF): m/z: 1139.7 [M+1] + ; elemental analysis calcd (%) for C74H94N2O4S2 : C 77.99, H 8.31, N 2.46, S 5.63; found: C 77.75, H 8.30, N 2.44, S 5.53.

Solution and thin-film absorption spectra were measured with conventional spectrophotometers. The solution and solid-state fluorescence spectra were recorded with Hitachi spectrophotometers at 25 8C. Solidstate quantum yields were measured on a fluorescence spectrophotometer with a calibrated integrating sphere system. Solid-state fluorescence lifetimes were measured based on time-resolved PL experiments which were made with a regenerative amplified Ti: sapphire laser (SpectraPhysics, Spitfire) at l = 400 nm (150 fs pulse width, second harmonic). PL images were recorded with an Olympus research inverted system microscope equipped with a CCD camera; the excitation source was a mercury lamp equipped with a band-pass filter (l = 330–380 nm). To measure the microarea PL spectra of a single microrod, microrods dispersed on a glass coverslip were excited with a UV laser (l = 351 nm, Beamlok, Spectraphysics). The excitation laser was filtered with a band-pass filter (330–380 nm), and then focused to excite the microrods with an objective lens (50  , N.A. = 0.80).

This research was financially supported by the Chinese Academy of Sciences, NSFC, and State Key Basic Research Program.

XRD measurements were carried out in reflection mode at room temperature. The thin-film surfaces were examined by tapping-mode AFM by using a Digital Instruments Nanoscope V atomic force microscope under ambient conditions. AFM samples and microscopic images were identical to those used in OFETs. Field-effect characteristics of the devices were

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FULL PAPER Organic Optoelectronic Materials Yonghai Li, Guanxin Zhang,* Wei Zhang, Jianguo Wang, Xin Chen, Zitong Liu, Yongli Yan, Yongsheng Zhao, &&&&—&&&& Deqing Zhang* Split personality: A series of arylacetylene-substituted naphthalene diimides (NDIs) are reported. These NDIs exhibit aggregation-induced emission enhancement behavior. Microrods of

three of the NDIs show typical optical wave-guiding behavior with relatively low optical loss. Moreover, these new NDIs exhibit n-type semiconducting properties (see figure).

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Arylacetylene-Substituted Naphthalene Diimides with Dual Functions: Optical Waveguides and n-Type Semiconductors

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