Synthesis of thiol-functionalized metal phthalocyanines-silver nanoparticles assemblies and their photophysics

In this paper, the photophysical properties of thiol-functionalized zinc phthalocyanine (ZnPc(SH)₈) conjugated with silver nanoparticles (AgNPs) were investigated. AgNPs were synthesized using modified citrate and tannic acid reduction methods, producing nanoparticles with distinct plasmonic features. ZnPc(SH)₈ was obtained via cyclotetramerization of tetra(alkylthio)phthalonitrile in the presence of zinc acetate and subsequently conjugated to AgNPs through thiol anchoring groups. UV-Vis spectroscopy confirmed the formation of ZnPc(SH)₈/AgNPs assemblies, showing characteristic ZnPc Soret and Q bands alongside AgNPs surface plasmon resonance bands. Variations in absorption intensity and band positions reflected differences in nanoparticle size, aggregation, and coupling strength. Fluorescence measurements revealed plasmon-mediated modulation of ZnPc emission, including quenching and enhancement effects depending on the AgNPs characteristics. Transient absorption spectroscopy indicated dominant ground-state bleaching and long-lived excited or charge-separated states, suggesting plasmon-molecule coupling and charge-transfer dynamics. Time-resolved fluorescence showed shortened singlet lifetimes in the presence of AgNPs, while phosphorescence measurements revealed prolonged triplet-state lifetimes, consistent with modified radiative and non-radiative decay pathways induced by plasmonic interactions. These results demonstrate that AgNPs conjugation significantly alters the photophysical behavior of ZnPc(SH)₈, highlighting the potential of ZnPc(SH)₈/AgNPs nanocomposites as plasmon-enhanced photosensitizers for photodynamic therapy and other photonic applications.