Electronic Absorption, MCD and Fluorescence Studies on Phthalocyaninatosilicon Covalently Linked to One or Two <font>TEMPO</font> Radicals

The UV-vis absorption, MCD and fluorescence spectra of phthalocyaninatosilicon ( SiPc ) covalently linked to one or two TEMPO radicals have been studied in comparison with those of (dihydroxy) SiPc . The electronic absorption and MCD spectra show little change on substitution of TEMPO radicals, indicating that the electronic interaction between excited singlet SiPc (1 SiPc *) and doublet TEMPO (2 TEMPO ) is very weak or non-existent. In contrast, fluorescence quantum yields decrease markedly with increasing number of TEMPO radicals. This result is interpreted reasonably by assuming that the decay from 1 SiPc * to excited triplet SiPc (3 SiPc *) partially becomes a spin-allowed transition owing to the interaction between 3 SiPc * and 2 TEMPO .