The Influence of Internal Rotation and Hydrogen Bonds onto the Excited State Lifetime of Indigo, Merocyanine and Triphenylmethane Dyes. I. Lifetime Measurements in the Picosecond Regime by Means of a Modelocked Dye Laser

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Abstract
Despite their high oscillatory strength f(S0 S1), the compounds under study do not show any appreciable fluorescence emission in solvents of low viscosity at room temperature. This lack of fluorescence is caused by fast nonracdiative relaxation processes which place the S1‐state lifetime in the picosecond regime. Applying a modelocked dye laser together with the techniques of “Ground State Repopulation” and “Two‐Photon Fluorescence”, respectively, we were able to measure them in various solvents with different viscosity and or polarity.