Hydrogen bonding, protonation and twisting in the singlet excited state of some 2‐(4‐Aminophenyl)pyrido‐oxa‐, ‐thia‐, and ‐imidazoles

Abstract

Abstract The absorption and fluorescence characteristics of 2‐(4‐aminophenyl)pyrido[3,2‐ d ]oxazole ( 1 ), of its thiazole 2 and imidazole 3 analogues, as well as of the corresponding pyrido[3,4‐ d ]imidazole 4 have been examined. S 1 is a planar ππ* ICT state, similarly to p ‐electron‐withdrawing substituted anilines. In the protonated form, the chromophore is the heterocyclic moiety. With compounds 3 and 4 in alcohols, hydrogen bonding depending on proton donating and accepting properties of the medium determines the fluorescence. In this case, a red‐shifted emission attributed to a twisted TICT state is also observed.