Light-emitting analogues based on triphenylamine modified quinoxaline and pyridine[2,3-b]pyrazine exhibiting different mechanochromic luminescence

Abstract

A series of light-emitting analogues, [4-(2,3-diphenyl-quinoxalin-6-yl)-phenyl]-diphenyl-amine (TPA–DPQ) and [4-(2,3-diphenyl-pyrido[2,3-b]pyrazin-7-yl)-phenyl]-diphenyl-amine (TPA–DPP) are synthesized and characterized. TPA–DPQ and TPA–DPP possess similar donor–acceptor structures, in which triphenylamine is used as an electron donor while 2,3-diphenyl-quinoxaline (DPQ) and its analogue 2,3-diphenyl-pyridine[2,3-b]pyrazine (DPP) serve as electron acceptors. Due to the stronger electron-withdrawing ability of DPP compared with DPQ, TPA–DPP exhibits longer but weaker emission than TPA–DPQ as expected. However, TPA–DPQ and TPA–DPP show different mechanochromic luminescence (MCL) properties with emission color changes of 42 and 10 nm, respectively. Crystallographic analysis demonstrates that changes of CH⋯π and CH⋯N intermolecular interactions are responsible for the significantly different MCL behaviors of the two compounds. This work will provide some guidance for the rational design of MCL-active fluorophores.