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, S-2 or S-3 (at energies of similar to26 300 cm(-1) and similar to30 000 cm(-1) above the S-0 state, respectively), the fluorescence from the S-1 state shows an ultrafast solvent-dependent rise, with characteristic times between 100 and 230 fs. The rise is attributed to S-n --> S-1 (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 S-1 state. (C) 2002 Elsevier Science B.V. All rights reserved.