Zinc Phthalocyanine N-Linked to Pyrroloperylenediimide Dyad: Significance of N-Connectivity in Modulating Photodynamics Toward Prolonging the Lifetime of Charge Separation

Abstract

A zinc phthalocyanine–pyrroloperylenediimide dyad connected through a nitrogen heteroatom (PDI-N-ZnPc) has been newly synthesized and characterized. Solvent-polarity-dependent singlet–singlet energy transfer and electron-transfer quenching were envisioned from absorption and steady-state fluorescence studies. Electrochemical and spectroelectrochemical studies enabled the assessment of the redox potentials of the donor and acceptor entities, as well as the spectral characterization of the one-electron oxidation and reduction products. Density functional theory (DFT) studies were performed to investigate the geometry and electronic structure, as well as the role of N-connectivity in determining the relative orientation of the entities. Further, time-dependent DFT studies helped establish the different excited states responsible for promoting charge separation. An energy diagram was subsequently established to visualize different photophysical events. Finally, femtosecond transient absorption spectral studies were performed in both nonpolar and polar solvents to observe energy- and electron-transfer events. The kinetic data were subsequently analyzed using global and target analyses. The persistence of the charge-separated state in the present dyad, compared with earlier reported ZnPc–PDI dyads featuring carbon–carbon connectivity, was the primary outcome of the present study, highlighting the role of heteroatom linkage in regulating electron-transfer dynamics in donor–acceptor conjugates.