Date Published: February 27, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Zheng Zhao, Han Nie, Congwu Ge, Yuanjing Cai, Yu Xiong, Ji Qi, Wenting Wu, Ryan T. K. Kwok, Xike Gao, Anjun Qin, Jacky W. Y. Lam, Ben Zhong Tang.
Furan‐cored AIEgen namely tetraphenylethylene‐furan (TPE‐F) is developed by diyne cyclization and its fluorescent and chemical properties are investigated and compared with its thiophene analogue. Results show that furan is superior to thiophene in terms of fluorescence, chromism, and charge transport. The mechanism of chromism of TPE‐F is investigated and its efficient solid‐state photoluminescence and good charge‐transporting property enable it to serve as light‐emitting material for the construction of electroluminescence devices with excellent performance. This work not only demonstrates an efficient strategy for constructing furan‐cored AIEgens but also indicates that they are promising as advanced optoelectronic materials.
The past decade has witnessed a burgeoning development of organic semiconductors for applications in various advanced electronic devices such as organic field‐effect transistors (OFETs), organic photovoltaics (OPVs), and organic light‐emitting diodes (OLEDs), flexible displays, and sensors.1, 2, 3, 4, 5, 6, 7, 8 To achieve a fast progress of organic semiconductors, efficient organic π‐functional materials are required. Among them, those carrying thiophene moiety play a significant role.9, 10 In addition to synthetic flexibility, a common argument for the wide use of thiophene‐derived materials is the strong polarizability of the sulfur atoms which gives rise to strong S…S and S…π intermolecular interactions for contributing high charge mobility.11, 12 Based on this cognition, a large number of thiophene‐derived semiconductors were developed and were found to exhibit superior device performances in OFETs, OPVs, sensors, etc.
The synthetic strategy for TPE‐F and TPE‐T is shown in Scheme1. Compound 1 was prepared by Glaser coupling of compound 2. Compound 1 then underwent cycloaddition in the presence of nucleophilic agent (S2− or OH−) and CuCl as catalyst, affording TPE‐F and TPE‐T in high yields. Since the two reaction steps proceeded with the same catalyst and solvent, one‐pot reaction was further implemented which gave rise to the same target compounds in satisfactory yields (Scheme 1B). Both TPE‐F and TPE‐T were carefully purified and fully characterized by NMR and mass spectroscopies (Figures S1−S6 in the Supporting Information). Their single crystals were obtained by slow evaporation of their dichloromethane (DCM)/hexane mixtures at ambient conditions and were analyzed crystallographically. TPE‐F and TPE‐T dissolved readily in common organic solvents (such as DCM, chloroform, and tetrahydrofuran) and showed high thermal stability, losing merely 5% of their weight at high temperature of 388 and 407 °C, respectively (Figure S7, Supporting Information). The glass‐transition temperature of TPE‐F and TPE‐T determined by differential scanning calorimetry was found at 129 and 125 °C, respectively (Figure S2, Supporting Information), which was suggestive of their high morphological stability (Figure S8, Supporting Information).
In summary, a furan‐cored AIEgen with bright emission, remarkable chromism, and favorable charge‐transporting property was synthesized by cascaded cyclization of diyne. The photophysical properties and mechanism of chromism of TPE‐F were investigated in details and compared with its thiophene analogue. Results showed that the extent of molecular planarity and intermolecular interactions as well as the packing density were responsible for giving different aggregates with varied color and emission. Based on its efficient solid‐state PL, charge transportation, and high thermal and morphological stabilities, nondoped OLED device of TPE‐F was fabricated which exhibited low turn‐on voltage, high brightness, and outstanding EL efficiencies, demonstrating the great potential of furan‐cored AIEgens in advanced optoelectronics.
Synthesis of TPE‐F and TPE‐T by Diyne Cyclization: To a round bottom flask were added compound 2 (100 mg, 0.14 mmol), CuCl (0.7 mg, 5% mmol), and KOH (2 mg, 0.04 mmol) in dimethylsulfoxide (DMSO) (2 mL), and H2O (0.1 mL) or Na2S⋅9H2O (33.6 mg, 0.14 mmol). The mixture was stirred at 120 °C for 30 min, giving TPE‐F in a yield of 82% or TPE‐T in quantitative yield.