Janus particle-type behavior of a model flavone derivative with distinct solvent-dependent competitive photoinduced processes

Abstract

In this article, Janus particle-type behavior, i.e. bi-faces character with respect to photoinduced charge transfer (CT) and proton transfer (PT) reactions, has been explored in the custom designed molecule 3-hydroxy-2-(4-(piperidin-1-yl)phenyl)-4H-chromen-4-one (HPPC), a molecule with both CT and PT sites. Solvent dependent distinct excited state CT and PT processes in HPPC have been explored using steady state and time resolved fluorescence spectroscopic measurements and quantum chemical calculations. The molecule HPPC shows only an excited state PT process in non-polar solvents like n-heptane and cyclohexane and a favorable CT over PT process in polar protic solvents like methanol, ethanol, propanol, and butanol, while competitive PT and CT processes in moderately polar solvents like 1,4-dioxane, chloroform, dichloromethane, acetonitrile, dimethylformamide, and dimethyl sulfoxide. Such a preferable solvent-dependent excited state PT and/or CT process makes HPPC a Janus-type particle. Structural calculations have been performed at density functional theory (DFT) levels and the theoretical potential energy curves (PECs) along the proton transfer and charge transfer coordinates, respectively, derived by using the DFT and TDDFT methods, suggest a low energy barrier for both excited state processes. The sensing behavior of HPPC towards Al³⁺ ions in aqueous medium as well as in non-aqueous medium was examined by enhanced fluorescence intensity.