Metal-free phthalocyanine aggregation and binding with amines: Specific and general solvent effects on absorption and fluorescence properties

Abstract The fluorescence and absorption properties of a metal-free phthalocyanine (Pc) H 2 PcR 4 and its zinc-centered complex ZnPcR 4 (R is the isopropyloxy at the β-position of a Pc ring) were measured and compared in protic and aprotic solvents. H 2 PcR 4 shows strong bonding interaction with amines and aggregation in alcohols in addition to the general solvent effect in aprotic solvents due to polarity change. The specific solvent effect leads to substantial changes in its spectra, fluorescence quantum yield ( Φ f ) and fluorescence lifetime ( τ f ) values. In contrast, ZnPcR 4 does not show the specific effects due to the presence of a central element in a Pc cavity. For H 2 PcR 4 the change of solvents caused a large variation of Φ f (0.050–0.48) and τ f (3.45–6.88 ns), in contrast to the slight changes for ZnPcR 4 . On the other hand, the general solvent effect of H 2 PcR 4 due to polarity is also more significant than that of ZnPcR 4 . The increase of solvent polarity decreases both Φ f and τ f , but increases the Stoke’s shift.