Photophysical Properties of Substituted Zinc Phthalocyanine-Dextran Systems

This study presents the synthesis of tetracarboxy ZnPc/dextran and octacarboxy ZnPc/dextran solutions and the investigation of their photophysical properties using UV–vis, transient absorption (TA), and emission spectroscopy. Nanosecond TA measurements are conducted using pump–probe techniques. ZnPc(COOH)₄ derivative exhibits efficient fluorescence, room-temperature phosphorescence in dimethyl sulfoxide/H₂O solution, with a quantum efficiency of 14.8% and lifetimes of 1.18 and 8.89 μs. The addition of dextran to ZnPc(COOH)₈ broadens the splitting of the two subbands in the Q band, leading to a characteristically strong far-redshift in the UV–vis absorption spectrum compared to the ZnPc(COOH)₄/dextran (DX) system. The triplet-state properties of ZnPc(COOH)₄/DX and ZnPc(COOH)₈/DX systems with an absorption region within the phototherapeutic window, the average lifetimes values of 4.86 and 5.17 μs, respectively, reveal them attractive as photosensitizing materials in photodynamic therapy. TA spectra of ZnPc(COOH)₄/DX and ZnPc(COOH)₈/DX conjugates measured at a pump pulse of 355 nm show positive and negative signals, indicating triplet–triplet (T–T) absorption and triplet–singlet (T–S) emission.