Nonradiative decay mechanisms of complexed indole derivatives studied by time-resolved fluorescence

Abstract

Ground and excited state characteristics of substituted indole derivatives reveal a sensitivity of indoles' electronic properties to the nature and location of substitutions on the indole ring. These substitutions affect both the nature of the excited electronic state and the susceptibility of this state to non-radiative decay processes. A number of mechanisms that deactivate the excited state have been identified including intersystem crossing, electron photoejection into polar solvents, and >N-H dissociation in polar solvents (see Glasser & Lami,1986) . While the >N-H group has been implicated in non-radiative decay processes in polar solvents, covalent substitutions elsewhere on the indole molecule may modulate the importance of this site in non-radiative decay mechanisms or alternatively these substitutions may introduce new deactivation mechanisms. Additionally, complexes formed between indole derivatives and β-cyclodextrin cavities show different sensitivity to excited state deactivation mechanisms dependent upon the location and nature of the covalent substitution. We have investigated the excited states of some indole derivatives substituted at position 5, para to the >N-H group on the benzyl ring, to determine the effect of such covalent substitutions on the fluorescence emission characteristics of the indole ring as well as on its susceptibility to alternate excited state decay mechanisms.