Laser Chemistry · 1983 · 21 citations · 0 references
Natural SciencesChemistryPhysicsChemical KineticsMolecular PhysicsSpectroscopyFluorescence SpectroscopyMolecular RotationOptical SpectroscopyPhotophysics Of Fluorescent ProbesRotational SpectroscopyDyestuff ChemistryFluorescence Quantum YieldFluorescent DyesFluorescent ProbesOrganic FluorophoresPicosecond SpectroscopySolvent Effects On FluorescenceSolvent Viscosity Effects
It was found that the weakly fluorescent trans‐2(4′‐ N,N ‐dimethylaminostyryl)‐ pyridinium betaine dyestuff (1) becomes efficiently fluorescent in very viscous media. The fluorescence quantum yield ( φ F ) for dyestuff (1) approaches unity in ethanol–ether (1: 1) glass at 98 K. Moreover, the fluorescence wave‐length is blue shifted (1874 cm −1 ) when the temperature is lowered to 98 K. The results are rationalized as being due to solvent viscosity dependent rate constant for a radiationless internal conversion process, involving rotation of the different parts of the molecule, a free rotor effect. The rate of internal rotation was estimated to be 3.4 × 10 11 s −1 . The results suggest that this molecule can be used as a fluorescent probe to study microscopic structural changes in surrounding media occurring on the picosecond time scale.