(A)symmetric chromophores based on cyano and fluorine-substituted 2,3-bis(5-arylthiophen-2-yl)quinoxalines: Synthesis, photophysical properties and application prospects

A series of novel V-shaped D-pi-A-pi-D push-pull chromophores, containing two aminoaryl electron donors (D), 1,5-thiophenylene pi-conjugated spacer and a 6-cyano-or 6,7-difluoroquinoxaline electron acceptor (A), was designed, synthesized, and characterized. 6-Cyano derivatives demonstrated red shift of absorption and emission maxima compared with 6,7-difluoro counterparts. The compounds displayed positive emission solvatochromism with increasing solvent polarity. Additionally, emission behavior of all compounds in THF/water mixture and solid state was investigated. Moreover, the two-photon excited fluorescence (2 PE) spectra of carbazolylcontaining chromophores were measured. Replacement of 6,7-difluoroquinoxaline core by 6-cyanoquinoxaline increases two-photon absorption cross section (delta(2PA)) value by more than 10 times. 6,7-Difluoroquinoxalines demonstrated changes in emission maxima or/and intensity after mechanic stimulation. Electronic-structure calculations with the use of quantum-chemistry methods were performed to have a deeper insight into experimental data. In summary, the obtained results show multifunctional nature of V-shaped 2,3-bis(5-arylthiephen-2yl)quinoxalines and their potential utility in diverse applications.