Synthesis, photophysical and photochemical studies of water soluble cationic zinc phthalocyanine derivatives

Peripherally and non-peripherally 2-diethylaminoethanethiol tetra-substituted zinc phthalocyanine (5a and 6a) and their quaternized derivatives (5b and 6b) have been synthesized and characterized. The quaternized derivatives (5b and 6b) show excellent solubility in aqueous medium. The photophysical and photochemical properties of the 2-diethylaminoethanethiol appended zinc phthalocyanine in dimethylsulfoxide (DMSO) for the non-ionic (5a and 6a) and in both DMSO and aqueous medium (phosphate buffered saline solution PBS, pH 7.4) (in the presence and absence of cremophore EL (CEL)) for the quaternized (5b and 6b) derivatives were studied and compared with that of the peripherally octa-substituted derivatives (7a and 7b). The complexes have intense absorption in the visible/near-IR region though the quaternized forms (5b, 6b and 7b) were slightly blue shifted and highly aggregate in aqueous solution. The triplet state quantum yields (ΦTΦT) and the triplet lifetimes (τTτT) were found to be higher in DMSO (ΦTΦT values ranged from 0.57 to 0.75 while τTτT values ranged from 190 to 220 μs in DMSO for all complexes) compared to aqueous medium (ΦTΦT values ranged from 0.15 to 0.17 while τTτT values ranged from 20 to 70 μs in pH 7.4 buffer). Addition of cremophore EL in aqueous solution resulted in induced disaggregation leading to increased ΦTΦT and τTτT.

Graphical abstractQuaternized peripherally and non-peripherally substituted 2-diethylaminoethanethiol tetrasubstituted zinc phythalocyanine gave low triplet yields and lifetimes in aqueous media which improved on addition of a surfactant, cremophore EL.Figure optionsDownload full-size imageDownload as PowerPoint slide