pH-induced “off–on–off” type molecular switch behaviors of zinc and free tetraimidazophthalocyanines

Abstract

Herein, the design and synthesis of pH sensing fluorophores, zinc(II) tetraimidazophthalocyanine (Pc-1) and metal free tetraimidazophthalocyanine (Pc-2), which present “off–on–off” type molecular switches were described. Their pH sensing properties have been investigated in detail in dimethylsulfoxide in the pH range of 2.0–15.0. The respective three forms of the molecules: deprotonated, neutral and protonated, were characterized by absorption and emission spectra as well as apparent pKa values (Pc-1: pKa₁ = 5.2 and pKa₂ = 14.3, Pc-2: pKa₁ = 4.9 and pKa₂ = 13.8). The protonation/deprotonation stages of imidazole groups of Pc-1 and Pc-2 present fluorescence-based “off–on–off” type molecular switch properties.