Acidic C-H Bond as a Proton Donor in Excited State Intramolecular Proton Transfer Reactions.

An unprecedented type of excited state intramolecular proton transfer in a series of benzo[h]quinoline (BHQ) derivatives substituted at position 10 with strong CH acid character is described using density functional theory/time-dependent density functional theory computational approaches with a hybrid functional and the 6-311++G(d,p) triple-ξ quality basis set. Our results show that for 10-malononitrile-substituted BHQ (2CNBHQ) the excited state intramolecular proton transfer C-H···N reaction is a barrierless process. Calculations also reveal that the reaction profiles of the 4-amino-substituted 2CNBHQ show a large dependence on the polarity of the environment.