Fluorescence of intramolecular electron donor—acceptor systems; the importance of through-bond interaction

Intramolecular electron donor—acceptor (EDA) systems have been studied in which D and A are separated by three carboncarbon sigma bonds. With D = (di)methoxyphenyl and A = 1,1-dicyanomethylene, such systems are found to show intramolecular charge-transfer (CT) type emission from a polar excited state even when the interconnecting sigma bonds are part of a rigid framework which prevents close approach between D and A. Through-bond interaction is proposed to provide the coupling between the ground state and the polar excited state in these systems.