Laser Chemistry
Volume 4 (1984), Issue 1-6, Pages 305-310
doi:10.1155/LC.4.305
Abstract
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 (φF) 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 × 1011 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.