Spectroscopic probing of acid–base properties and photocharacterization of phthalocyanines in organic solvents and polymer matrices

This work reveals spectral characterization of newly synthesized metal-free (Pc-1) and Zn(II) (Pc-2) phthalocyanines (Pcs) in conventional solvents and two solid matrices; ethyl cellulose (EC) and polyvinyl chloride (PVC). Fluorescence lifetime (τF) and fluorescence quantum yield values (ϕF) of the Pcs were calculated in tetrahydrofuran (THF), dimethylsulfoxide (DMSO) and solid matrices of EC and PVC. The respective protolytic forms were characterized by absorption and emission spectra as well as apparent pKa values. The immobilized metal-free phthalocyanine exhibited strong and pH-dependent fluorescence due to a protolytic equilibrium within a large pH range yielding three different pKa values. The Zn-II phthalocyanine also exhibited optical emission based response to proton in the pH range of 2.0–9.0. Upon exposure to proton, reversible relative signal changes for PVC-doped Pc-1 and Pc-2 were approximately 90 and 95%, respectively. Presence of polyvalent metal ions in test medium did not restrict the proton sensing ability of the dyes.