Theoretical study on influence of geometry controlling over the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline and its derivatives

Abstract

© 2017 Elsevier B.V. A structural modification on quinoline as a proton donor of 10-hydroxybenzo[h]quinoline (HBQ) giving different HBQ derivatives greatly affects their photophysical properties. In this study, the excited-state intramolecular proton transfer (ESIPT) reactions of HBQ and its derivatives with different geometries have been systematically investigated using DFT and TD-DFT at B3LYP/TZVP. Calculated absorption and emission spectra are used to describe the photophysical changes in which the absorption spectra of HBQ derivatives are blue-shifted compared with that of HBQ while their emission spectra are blue-shifted except those of 3,4-dihydro indene[1,2-b]pyrrole-8-ol (IPRO) and 2-(4H-pyrrol-2-yl)phenol (PRP) compounds with different proton donor and connecting moiety are red-shifted. From results of potential energy curves along the proton transfer (PT) coordinate, PT is favorable in the excited-state but not in the ground state. On-the-fly dynamics simulations in the excited-state are further employed to determine reaction mechanisms and the time evolution of PT. The ESIPT process easily occurs in most of the compounds except the IPRO with much high PT barrier. The ESIPT times in most compounds take place within 100 fs and PT probability is nicely anti-correlated with the PT barrier. Thus, the geometry changes alter the electronic spectra but do not affect ESIPT of HBQ derivatives. Moreover, once the PT is complete, the internal conversion is initiated by twisted skeleton, leading to lower intensity of tautomer emission.