Excitation Wavelength Dependence of Phosphorescence and Hydrogen-Bonding Formation of Thioxanthone and 2,4-Diisopentylhioxanthone

Abstract

Abstract Phosphorescence spectra of the ethanol solutions of thioxanthone(TX) and 2,4-diisopentylthioxanthone (DITX) exhibited excitation wavelength dependence at 77 K. In addition to the normal phosphorescence observed at 450 nm for TX and at 460 nm for DITX, a new red-shifted phosphorescence was resolved at 470 nm and 485 nm, respectively, when TX and DITX were excited at the absorption tail. The lifetimes and excitation spectra of the red-shifted phosphorescence were found to differ from those of the normal phosphorescence. Based on the study on UV absorption spectra and phosphorescence spectra measured with hydrated species of TX and DITX in ethanol–water solution at 77 K, the red-shifted phosphorescence is ascribed to the hydrogen-bonded species with water. In 2-methyltetrahydrofuran, phosphorescences of TX and DITX shift to the longer wavelengths and the lifetimes become longer when excited at the longer absorption tail, although the phosphorescence excitation spectra do not change appreciably.