Femtosecond fluorescence upconversion study of a boron dipyrromethene dye in solution

A femtosecond fluorescence upconversion study is reported for the boron-dipyrromethene (BDP) dye, 2,6-diethyl-1,3,5,7-tetramethyl-8-phenyl-4-difluorobora-3a,4a-diaza-(s)-indacene (BDP-1), dissolved in cyclohexane, chloroform and acetonitrile. After pulsed photoexcitation into the higher excited states, S2 or S3 (at energies of ∼26 300 cm−1 and ∼30 000 cm−1 above the S0 state, respectively), the fluorescence from the S1 state shows an ultrafast solvent-dependent rise, with characteristic times between 100 and 230 fs. The rise is attributed to Sn→S1 (n=2,3) internal conversion followed by vibrational relaxation. In addition, the BDP-1 fluorescence shows picosecond transient behavior that is attributed to vibrational cooling in the excited S1 state.