The ConPET Mechanism Remains Veiled: Reply to “Unlocking the ConPeT Mechanism”

This Reply addresses Ceroni's Correspondence, which proposed a revised electron transfer (ET) mechanism for the cyanoarene-photocatalyzed consecutive photoinduced electron transfer (ConPET) process via time-resolved spectroscopy. While their model highlights solvated electrons from the excited radical anion 3,4,5,6-tetrakis(diphenyl amino)phthalonitrile (4DPAPN^•−), new experimental and theoretical analyses underscore the plausibility of the original proton-coupled electron transfer (PCET)/ConPET pathway. Rigorous reinvestigation under controlled conditions reaffirms the complexity of the mechanism and calls for further spectroscopic and computational studies to resolve these interplaying pathways. The discussion advances the debate on photoredox mechanisms, offering actionable strategies for future mechanistic elucidation.

Abstract

In this journal, a Correspondence by Ventura, Cozzi, and Ceroni reported time-resolved absorption spectroscopy studies in the electron transfer process from cyanoarene photocatalyst 3,4,5,6-tetrakis(diphenyl amino)phthalonitrile (4DPAPN) in the presence of tetrabutylammonium oxalate (TBAOx). This was used as a model reaction to investigate the mechanism of consecutive photoinduced electron transfer (ConPET) in our previously reported asymmetric [3+2] photocycloaddition. They proposed a new electron transfer pathway in which the electron from the excited state of the radical anion 4DPAPN*^•− solvated in acetonitrile. This article replies to their Correspondence, including: the experimental and theoretical analysis on the driving force of electron transfer and a series of new experiments conducted with purer reagents under more stringent conditions, which suggest that the process of proton-coupled electron transfer (PCET) followed by ConPET cannot be excluded, as proposed in our previous publication. Yet, Ceroni et al.’s efforts to study organic photochemical reactions using time-resolved spectroscopy remain worthwhile, and their proposed mechanism also led us to consider other possible pathways for the reaction. This article concludes with a series of constructive suggestions for further studying the ConPET mechanism using time-resolved absorption spectroscopy and other techniques.

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