Theoretical regulation of ESIPT behavior by varying the π-expansion of proton acceptor for substituted hydroxyl fluorenes

Abstract

• The π stacks size in proton acceptor affects ESIPT behavior of substituted hydroxyfluorenes. • The enhancement of hydrogen bond facilitates ESIPT process. • The charge redistribution is favorable for promoting the ESIPT reaction. ESIPT reaction is one of the most extensively studied photochemical behaviors, and many organic chromophores are designed based on this mechanism. Oxazolinyl- and arylchalcogenazolyl-substituted hydroxyfluorenes are emission color-tunable chromophores, and they are used as efficient proton receptors in ESIPT-based chromophores. In this work, we concentrate on probing into the ESIPT behaviors of oxazoline-substituted hydroxyfluorenes (Oxa-OH), hydroxylated benzoxazole (BO-OH) and naphthoxazole (NO-OH) compounds. The π-extended constructions of proton receptors of these three compounds are expended successively. Structures are optimized and infrared (IR) spectra of electron excited state are calculated. Independent Gradient Model (IGM) function is also used to compare hydrogen bond interactions, and frontier molecular orbitals are further analyzed. It is found charge redistribution is favorable for promoting ESIPT process. The effect of π-expansion of proton acceptor on ESIPT behavior is also observed. Especially, the potential application of π-expansion in color regulation of crystal luminescence is promising.