Rotational relaxation in the lowest triplet states of 2,4,6-triisopropylbenzophenones in solutions at room temperature studied by picosecond laser spectroscopy

The triplet–triplet absorption spectra due to the lowest triplet states of meta- and para-substituted dicarbonyls of 2,4,6-triisopropylbenzophenone in solutions at room temperature shifted progressively to the blue with time on the subnanosecond time scale. The shift times were affected by changing the substituent X and their position of substitution as well as the viscosity of solvents. These results were interpreted in terms of the conformational change in the lowest triplet states.