A Theoretical Study on Rate Constants of Excited State Proton Transfer Reaction in Anthracene-Urea Derivatives

Abstract

Abstract We elucidate the origin of the two types of observed fluorescence in a complex consisting of nPUA (1-anthracen-n-yl-3-phenylurea; n = 1, 2, 9) and an acetate ion. By calculating the molecular properties related to the proton transfer reaction in the excited state, we clarified a correlation between the acid dissociation constant in the excited state (pKa) in the urea moiety and the rate constant of the excited state proton transfer reaction. The computed pKa suggests that the proton on the anthracenyl group side is transferred in the case of 1PUA and 2PUA, whereas the proton on the phenyl group side is transferred in 9PUA. Low pKa and activation barriers were calculated for 9PUA, which causes the stability of 9PUA due to the absence of the planarity after the proton transfer reaction.