GEOMETRY-DEPENDENT AND SOLVENT-POLARITY-DEPENDENT PHOTOINDUCED ELECTRON-TRANSFER IN CONFORMATIONALLY RESTRICTED MAGNESIUM FREE-BASE HYBRID DIPORPHYRINS

Excited-state dynamics of a series of conformationally restricted magnesium-free-base hybrid diporphyrins (MgP-H2P) have been studied by fluorescence lifetime measurement and picosecond time-resolved transient absorption spectroscopy. Upon photoexcitation in toluene and THF, intramolecular singlet-singlet energy transfer from the 1(MgP)* to the H2P has been observed regardless of the spacer between the two subunits and the 1(H2P)* thus formed decays with the same time constant with the reference monomeric H2P in each solvent. In DMF, the photoexcited state dynamics of MgP-H2P depends on the geometry of the models; charge separated state (MgP)+-(H2P)- is generated from both of the 1(MgP)* and 1(H2P)* in hybrid diporphyrins with shorter separation, while only the singlet-singlet energy transfer from the 1(MgP)* to the H2P has been observed for models with larger separations.