Excited-State Intramolecular Proton Transfer in 2-(2-Hydroxyphenyl)benzimidazole and -benzoxazole: Effect of Rotamerism and Hydrogen Bonding

作者: Kaustuv Das , Nilmoni Sarkar , Ajit Kumar Ghosh , Devashis Majumdar , Deb Narayan Nath

DOI: 10.1021/J100088A006

关键词: Excited stateConformational isomerismQuantum yieldChemistryPopulationTriplet stateTautomerPhotochemistryEmission spectrumGround state

摘要: An excited-state intramolecular proton transfer (ESIPT) process in 2-(2’-hydroxyphenyl) benzimidazole and -benzoxazole (HPBI HBO, respectively) has been studied using steady-state time-resolved emission spectroscopy at various temperatures by semiempirical quantum chemical methods. For both of them two distinct ground-state rotamers I I1 respectively responsible for the “normal” “tautomer” have detected. In hydrocarbon solvents room temperatureand 77 K tautomer predominates over normal HPBI HBO. This indicates that rotamer 11, emission, is intrinsically stabler than I, which causes emission. alcoholic glass a dramatic enhancement observed. It suggested due to increased solvation, more polar becomes alcohol substantial temperature variation change population with temperature. From detailed medium energy difference between determined. dioxane-water mixtures it observed addition water yield increases, ascribed inhibition ESIPT formation an intermolecular hydrogen bond involving water. CNDO/S-CI calculations were performed optimizing thegroundstate geometry AM1 method. Details energy, dipole moment, charge distribution ground state (SO) first excited singlet (SI) barrier interconversion SO, SI, triplet are discussed. The calculation too high (SI TI) free interconversion.

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