Reorientation of hydrogen-bonded solvents around a large dipole

Using picosecond spectroscopy, we find rise times τ_R ? 20 ps for p-dimethylaminobenzonitrile S₂ → S₀ fluorescence in the weakly hydrogen-bound alcohols 2,2,2-trifluoroethanol and 2-fluoroethanol. Since we previously obtained τ_R ≈ 40 ps in methanol and ethanol, this provides evidence that hydrogen-bonding-retarded solvent reorientation largely governs the fluorescence in these solvents.