pH-induced "off-on-off" type molecular switch behaviors of zinc and free tetraimidazophthalocyanines

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: pKa(1) = 5.2 and pKa(2) = 14.3, Pc-2: pKa(1) = 4.9 and pKa(2) = 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.