Picosecond Generation of Transient Charge Carriers in Langmuir-Blodgett Films of Semi-Amphiphilic Heterodimers

Abstract : Langmuir-Blodgett homolayers are formed by deposition of semi-amphiphilic porphyrin-phthalocyanine heterodimers. The optical and photophysical properties of these dimers have been investigated and compared to the liquid-phase data. Excitation of the dimer results in an instantaneous formation of the singlet excited states, followed by a very efficient charge-transfer reaction. The oxidized porphyrin and reduced phthalocyanine moieties are formed within 2 ps and disappear in 70 ps. The triplet excited states of the porphyrin issued from the intersystem crossing decay pathway of the singlet excited states are formed with a very low quantum yield. They also undergo a charge-transfer reaction, leading to the formation of long-lived transient charge carriers. The photoprocesses determined in the Langmuir-Blodgett films of semi-amphiphilic porphyrin-phthalocyanine heterodimers are almost identical to those previously observed for the same dimers in the liquid phase.