Femtosecond study of S2 fluorescence in malachite green in solutions

By using femtosecond fluorescence spectroscopy, the relaxation kinetics of the second electronic excited state (S-2) in malachite green has been investigated in several solvents with different viscosity. The decay time of the S-2 fluorescence in water solution is obtained to be 0.27 ps and the internal conversion rate from the S-2 state to the S-1 state is estimated as (1.2 ps)(-1). It has also been found that the S-2 decay kinetics consists of fast and slow components in high-viscosity solvents. The S-2 relaxation is explained in terms of the internal conversion and the torsional configuration change of molecules. (C) 1998 Elsevier Science B.V.