Photophysical properties of nonperipherally and peripherally substituted triazatetrabenzcorrole phosphorous dihydroxy and singlet oxygen generation

Triazatetrabenzcorrole (TBC) is the nonplanar analogue of phthalocyanine (Pc), in which one meso-nitrogen is missing. A nonperipherally substituted TBC complex, i.e. tetra(α-phenoxy) TBC phosphorous dihydroxy (POTBC(α-OPh)4) was synthesized and characterized for the first time together with a peripherally substituted POTBC(β-OPh)4. The photophysical properties for each POTBC complex and its corresponding zinc Pc counterpart were measured by ground state absorption, steady state fluorescence, single photon counting technique and laser flash photolysis methods. These compounds possess long triplet lifetime, good triplet formation yield. They can effectively photosensitize the generation of singlet oxygen 1O2(1Δg). Their fluorescence yield and lifetime are comparable to the corresponding zinc Pcs. The nonperipheral α-OPh exhibits remarkably larger influence than the peripheral β-OPh on the photophysical properties, including: (1) the longer red shift for absorption, fluorescence spectra and T1–Tn transient spectra and (2) the larger decrease of fluorescence lifetime and triplet lifetime. Although POTBC complexes are nonplanar in the structure, they still show the similar effect of nonperipheral substitution on the photophysical properties as that of the planar ZnPcs.