Modulation of ESIPT fluorescence in o-hydroxy acetophenone derivatives: A comparative study in different bio-mimicking aqueous interfaces

Abstract

Excited state intramolecular proton transfer (ESIPT) reaction and photophysical behavior of two intramolecularly hydrogen bonded o-hydroxy acetophenone derivatives, namely 2-acetyl-4-methyl-6-nitrophenol (I) and 2-acetyl-4-chloro-6-nitrophenol (II) are studied in the presence of different micro-heterogeneous environments ranging from cyclodextrin, surfactant as well as in model water soluble proteins like bovine and human serum albumin. The appearance of different emission profiles corresponding to a series of excited state isomers like primary enol structure (E), proton transferred keto form (K), or intermolecularly hydrogen bonded (with the solvent) open conformer is rationalized on the basis of varying degree of sequestration and the environment around the probe in the local micro-structure of the hydrophobic domain. The experimental observations are in complete agreement with the fluorescence behavior of these probes in homogeneous solvent medium as well as results based on density functional theory calculation published earlier (Chem. Phys. 342, 2007, 309).