Photophysical and photochemical parameters of octakis (benzylthio) phthalocyaninato zinc, aluminium and tin: Red shift index concept in solvent effect on the ground state absorption of zinc phthalocyanine derivatives

This paper addresses the synthesis of octa-substituted benzylthio metallophthalocyanines (OBTMPcs) that contain the central metal ions of Zn ²⁺, Al ³⁺ and Sn ⁴⁺. The ground state absorption of ZnPc(SR) ₈ (OBTZnPc) along with the ZnPc derivatives, well documented in literature were used to study a new concept called the red shift index ( R _sI ). The concept is based on the empirical values of R _sI of the different complexes in solvent media. Unequivocally, parameters used in this paper show strong correlations that are consistent with the results obtained. For instance, R _sI of the complexes tend to increase as the refractive index, n _D, and solvent donor, DN, of solvent increases. Photodegradation (photobleaching) quantum yield, ϕ _d measurements of these compounds show that they are highly photostable, ϕ _d (0.03-0.33 × 10 ^-5). The triplet quantum yield, ϕ _T (0.40-0.53) and the triplet lifetime, τ _T (610-810 μs) are within the typical range for metallophthalocyanines in DMSO. The photosensitisation efficiency, S_Δ, is relatively high for all the molecules (0.74-0.90).