Excited state dynamics of triphenylmethane‐dyes used for investigation of microviscosity effects

Abstract

Abstract The nonexponential fluorescence decay behaviour of triphenylmethane‐(TPM)‐dyes can be understood as barrierless relaxation, i.e. intramolecular rotational relaxation of dialkylanilino groups under the influence of a driving force. The observed viscosity dependent rotational relaxation rates of TPM‐dyes with large and small, rigid and flexible rotor groups do not obey the Debye‐Stokes‐Einstein relationship but can be fitted within the microviscosity theory of Gierer and Wirtz and show that free volume effects are important. The relative size of free volume effects in n‐alcohols, diols and glycerol can be determined by comparing the rates of different TPM‐dyes.