Morpholine-Phthalocyanine (Donor-Acceptor) Construct: Photoinduced Intramolecular Electron Transfer and Triplet Formation from its Charge Separation State

Silicon phthalocyanine (SiPc) with two axially attached morpholine (MP) units was prepared, and its photophysics was studied by laser flash photolysis, steady state and time-resolved fluorescence methods. Both the fluorescence efficiency and lifetime of SiPc moiety were remarkably quenched, because of the efficient intramolecular photoinduced electron transfer (PET) from morpholine donors to SiPc moiety. The generated charge separation state (CSS), SiPc center dot- MP center dot+, which was observed by transient absorption spectra, showed a lifetime of 4.8 ns. The triplet quantum yield of SiPc unit in the supramolecule is unexpectedly high, and the predominant spectral signal in microsecond-scale is triplet-triplet (T-1-T-n) absorption. This high triplet yield is due to the charge recombination of CSS that generates T-1 in 32% efficiency: SiPc center dot--Mir(center dot+) -> (SiPc)-Si-3 MP. The T-1 formation process occurred efficiently because the CSS SiPc center dot- -MP center dot+ has a higher energy (1.65 eV) than that of the triplet state (SiPc)-Si-3-MP (1.0 eV). Emission from the CSS was also observed: SiPc center dot--MP center dot+ -> SiPc-MP + hv'.