LASER FLASH STUDIES OF THIOINDIGO AND INDIGO DYES - EVIDENCE FOR A TRANS CONFIGURATION OF THE TRIPLET-STATE

The triplet-triplet absorption spectra of thioindigo, 5,5′-di-t-amylthioindigo, 5,5′-di-neopentylthioindigo, and N,N′-diacetylindigo in glycerol triacetate (GT) and in EPA were found to be practically the same in fluid and rigid media. The logarithms of the first order decay rate constants depend linearly on T-1. In GT and 2-methyltetrahydrofuran (MTHF) temperature and viscosity cause a strong decrease of φt-c, whereas the right yield remanis constant. The results indicate that the lowest triplet state of the thioindigo dyes has predominantly a planar trans configuration (tr3). The twisted configuration (p3) is suggested to be in thermal equilibrium with tr3 at room temperature. Triplet decay in liquid solution occurs via intersystem crossing from p3 to the twisted ground state (p3 - p0). © 1979.