Rationalize the roles of electron donating-withdrawing groups in the impacts on solvatochromism, nonlinear optics, and electroluminescence devices

The correlation between chemical structure and photophysical behavior is vital for development of luminogens in the application of optoelectronics. Different donor, acceptor and π-bridge were systematically combined to produce a series of D-π-A-π-D chromophores, TATCN, CATCN, and TAPCN, in which the diphenylamine, carbazole, and terephthalonitrile groups served as electron donor-acceptor pairs and benzene and thiophene rings were chosen as π-bridge. The use of diphenylamine provided higher energy of HOMO, and the utilization of terephthalonitrile linked by thiophene gave lower energy of LUMO. Therefore, the variation of transition energy can be guided in this teraryl system. Moreover, the solvatochromic experiment and corresponding Lippert-Mataga analysis revealed the multiplicity of emission wavelength and change of transition dipole moment where the emitting color covered the whole region of visible light. Such design of the molecule exhibited quadrupolar structure and thus a significant response of two-photon absorption was observed. All of these three compounds exhibited high fluorescence quantum yields ranged from 90% to 50% in cyclohexane and tetrahydrofuran, and the preliminary test of electroluminescence showed the application potential for these three chromophores. The result also suggested the adoption of thiophene might benefit the performance of device. This systematical exploration presented the roles of organic functional groups influencing photophysical properties, and a platform for developing highly fluorescent luminogens.