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

TLDR: The non-ponential fluorescence decay behavior 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 as discussed by the authors.

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.