Photo-induced charge separation vs. Degradation of a BODIPY-based photosensitizer assessed by TDDFT and RASPT2

Ziems, Karl Michael, Gräfe, Stefanie and Kupfer, Stephan (2018) Photo-induced charge separation vs. Degradation of a BODIPY-based photosensitizer assessed by TDDFT and RASPT2. Catalysts, 8 (11), [520]. (doi:10.3390/catal8110520).

Abstract

A meso-mesityl-2,6-iodine substituted boron dipyrromethene (BODIPY) dye is investigated using a suite of computational methods addressing its functionality as photosensitizer, i.e., in the scope of light-driven hydrogen evolution in a two-component approach. Earlier reports on the performance of the present iodinated BODIPY dye proposed a significantly improved catalytic turn-over compared to its unsubstituted parent compound based on the population of long-lived charge-separated triplet states, accessible due to an enhanced spin-orbit coupling (SOC) introduced by the iodine atoms. The present quantum chemical study aims at elucidating the mechanisms of both the higher catalytic performance and the degradation pathways. Time-dependent density functional theory (TDDFT) and multi-state restricted active space perturbation theory through second-order (MS-RASPT2) simulations allowed identifying excited-state channels correlated to iodine dissociation. No evidence for an improved catalytic activity via enhanced SOCs among the low-lying states could be determined. However, the computational analysis reveals that the activation of the dye proceeds via pathways of the (prior chemically) singly-reduced species, featuring a pronounced stabilization of charge-separated species, while low barriers for carbon-iodine bond breaking determine the photostability of the BODIPY dye.

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Contributors

Author: Karl Michael Ziems

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