Effect of Direct Alkyne Substitution on the Photophysical Properties of Two Novel Octasubstituted Zinc Phthalocyanines

The synthesis and characterization of two new alkynyl-substituted phthalonitrile derivatives and their peripherally octasubstituted zinc phthalocyanine (ZnPc) compounds were reported. The aggregation behavior of phthalocyanines was investigated. Fluorescence quantum yields, lifetimes, and quench studies of phthalocyanines were examined. The photophysical parameters obtained for synthesized phthalocyanines were compared with each other and with the unsubstituted ZnPc used as a standard.

Abstract

The synthesis of two novel phthalonitrile derivatives (3–4) bearing ethynylcyclohex-1-ene and ethynylcyclohexane groups and two peripherally octa substituted zinc (II) phthalocyanines (5–6) were prepared. The synthesis of phthalonitrile derivatives was performed with Sonagashira coupling reaction by using palladium-catalyzed. The newly synthesized compounds were characterized by using FT-IR, NMR, mass, and UV-Vis absorption spectroscopy techniques. Aggregation studies of 5 and 6 were performed in various organic solvents and different concentrations in tetrahydrofuran (THF). The photophysical studies of the Pcs were performed in THF to determine the effect of the alkyne groups on the fluorescence of the Pc ring. Substances showing fluorescence properties can be used in practical applications such as to create an image in microscopy. Fluorescence quantum yield (Φ_F) and fluorescence lifetime (τ_F) of 5–6 were calculated. The fluorescence quenching studies of 5–6 were performed by adding the different concentrations of 1,4-benzoquinone (BQ) to a constant concentration of the Pcs in THF and it was found that benzoquinone was an effective quencher. The values of the Stern-Volmer constant (K_sv) and quenching constant (k_q) of zinc phthalocyanines (5–6) were examined. All obtained results were compared with each other and with unsubstituted zinc Pc compound used as a reference.

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