Efficient Intramolecular Fluorescence Quenching in Triphenylmethane‐Dyes Involving Excited States with Charge Separation and Twisted Conformations

Abstract

Abstract The high fluorescence quantum yields ϕ f of most Triphenylmethane(TPM)‐dyes and carbon‐bridged TPM‐dyes in highly viscous solutions ( ϕ f ranging from 0.3 to 0.8) decrease with increasing temperature by a factor > 100, due to viscosity dependent nonradiative deactivation. The deactivation rates k rd of bridged model dyes are significantly smaller (by a factor of up to 170) as compared to k rd of the unbridged crystal violet. ‐ Application of the Twisted Intramolecular Charge Transfer (TICT)‐model to neutral and ionic TPM‐dyes yields an explanation for the different behaviour of similarly structured compounds. The influence of steric and electronic factors on various TPM‐dyes is discussed within this framework. This leads to a simple rule involving donor and acceptor properties of molecular subunits, which permits the prediction of fluorescence properties (high quantum efficiency for laser dyes or ultrafast deactivation for saturable absorbers).