Understanding the details of aggregation-induced emission (AIE) effect in D-π-A type imidazolium-based compounds through the stepwise change of rotatable moieties

The AIE behaviors of two D-pi-A type imidazolium-based compounds 4a and 4b have been studied. 4a is a typical AIE-active molecule, whereas 4b is not. The experimental and computational work demonstrates that the AIE effect mainly depends on the restricted rotation of imidazolium unit (electron acceptor, A) in aggregate state, rather than TPA group (electron donor, D).