A competitive effect of acceptor substitutions on the opto-electronic features of triphenylamine cored di α-cyanostilbene derivatives

Abstract

Three novel triphenylamine cored di-branched α-cyanostilbenes with different electron-acceptors [H (neutral), CF₃, and NO₂] were synthesized. All the compounds exhibited a distinct positive solvatochromism dependent on the polarity and nature of the acceptor unit. Emission in binary solvent mixture reveals that CF₃ substituted chromophores promote the AIE effect with moderate emission wavelength shift. In contrast, NO₂ substitution drives the emission to a longer wavelength due to pronounced ICT but with quenched emission. Introducing CF₃ and NO₂ into a single molecule has a competing effect, i.e., balancing the pull–pull interactions enabled the enhancement of ICT characteristics with a moderate ACQ to AIE effect. These studies reveal that electron-accepting functionalities create a considerable impact on an otherwise identical template's optoelectronic characteristics. DFT and TDDFT analysis correlate the absorption and wavelength shift with acceptor functionality, and DOS-PDOS analysis helps predicting their photophysical characteristics upon photoexcitation. PES scan studies demonstrated that arms with strong acceptor units increased the energy barrier of dynamic intramolecular rotation of the α-cyano unit.