Tracking photoinduced charge separation in a perfluorinated Zn-tetraphenylporphyrin sensitizer

Abstract

The development of artificial biomimetic systems with real-world applications relies on a profound understanding of all photophysical and photochemical processes taking place upon light absorption by a chromophoric unit. Efficient photoinduced charge separation in photosensitizers or specialized photocatalysts is the process triggering most of the chemical reactions in the production of solar fuels, and hence, its proper characterization is of utmost importance. In this work, we investigated photoinduced charge separation processes in a perfluorinated Zn-tetraphenylporphyrin photosensitizer (ZnF₂₀). Ascorbate and 1,4-diazabicyclo[2.2.2]octane (DABCO) were used as reversible electron donors for nanosecond-resolved pump–probe experiments using both optical absorption and resonance Raman scattering as probes. Our results indicate that in spite of similar charge separation efficiencies, the DABCO-containing system exhibits a much faster kinetics of charge-separated state formation and decay. This is attributed to its inherent ability to coordinate to the metal center. Time-resolved resonance Raman measurements allow for the detection of vibrational modes specific to both the triplet excited state of ZnF₂₀ and its reduced state, complementing transient absorption data to fully characterize the charge separation process.