The Influence of Viscosity on Fluorescence‐Quantum‐Yields of a Polymethine‐Dye Dichinolyl‐Cyano‐Methane

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Abstract
Among a series of heteroannular polymethines, Dichinolyl‐Cyano‐Methane excells by its large dynamic range of fluorescence‐quantum‐yield in response to solvent fluidity. The excited‐state‐dynamics of this probe and the influences of various solvents on it are studied and compared with expectations from current models of the subject. A pronounced viscosity(temperature)‐dependent D‐effect on fluorescence‐quantum‐yield in fluid solution was found and explained by coupling of the dominant and viscosity‐dependent relaxationmode to a intramolecular H/D‐bridge‐potential. The observations presented indicate, that Dichinolyl‐Cyano‐Methane may serve as a diagnostic tool in future studies on fluid‐dynamics.