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- 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 ; A.J.S., M.K.C., and D.T.G. gratefully acknowledge the Foundation for Polish Science for supporting this work under Project MPD/2010/4 ("Towards Advanced Functional Materials and Novel Devices-Joint UW and WUT International PhD Programme"). This work has been also supported by the Ministerio de Economia y Competitividad (MINECO) of Spain (Project CTQ2011-23156/BQU) and the Generalitat de Catalunya (Project 2014SGR931, Xarxa de Referencia en Quimica Teorica i Computacional, and ICREA Academia 2014 prize for M.S.). A.J.S. gratefully acknowledges the European Social Fund through the Warsaw University of Technology Development Programme, realized by the Center for Advanced Studies