PICOSECOND TRANSIENT ABSORPTION-SPECTROSCOPY ON 13(2)-HYDROXY-BACTERIOPHEOPHORBIDE-METHYLESTER (OH-BPME) MOLECULES IN SOLUTION AND EMBEDDEDIN MIXED LANGMUIR-BLODGETT-FILMS

Transient absorption spectroscopy was carried out on OH-BPME in methan ol and on multilayer mixed OH-BPME/behenic acid Langmuir-Blodgett (LB) films after resonant excitation of the S-2 state by 17 ps single puls es. The time dependences of saturable absorption of the S-0-S-2 and S- 0-S-1 transitions and of the Stokes shifted transient amplification of the probe photons are investigated. From the latter a lifetime of the S-1 state of 1.7 ns and from the first an ISC quantum efficiency of 0 .5 are obtained on OH-BPME in methanol, which is supported by the stro ng induced absorption band observed around 600 nm caused by triplet-tr iplet absorption processes. In comparison to the saturable absorption a delayed starting of the transient amplification is observed speaking for a relatively long lifetime of the molecules in the S-2 state. The spectra of the LB films are dominated by aggregates of OH-BPME caused by the high package density. An excitation induced decrease of the ab sorption coefficient at the S-0-S-1 transition of the aggregate at 815 nm is observed with a very short decay time of 85 ps.