Issue 1, 2023

Sensitizer-controlled photochemical reactivity via upconversion of red light

Abstract

By combining the energy input from two red photons, chemical reactions that would normally require blue or ultraviolet irradiation become accessible. Key advantages of this biphotonic excitation strategy are that red light usually penetrates deeper into complex reaction mixtures and causes less photo-damage than direct illumination in the blue or ultraviolet. Here, we demonstrate that the primary light-absorber of a dual photocatalytic system comprised of a transition metal-based photosensitizer and an organic co-catalyst can completely alter the reaction outcome. Photochemical reductions are achieved with a copper(I) complex in the presence of a sacrificial electron donor, whereas oxidative substrate activation occurs with an osmium(II) photosensitizer. Based on time-resolved laser spectroscopy, this changeover in photochemical reactivity is due to different underlying biphotonic mechanisms. Following triplet energy transfer from the osmium(II) photosensitizer to 9,10-dicyanoanthracene (DCA) and subsequent triplet–triplet annihilation upconversion, the fluorescent singlet excited state of DCA triggers oxidative substrate activation, which initiates the cis to trans isomerization of an olefin, a [2 + 2] cycloaddition, an aryl ether to ester rearrangement, and a Newman–Kwart rearrangement. This oxidative substrate activation stands in contrast to the reactivity with a copper(I) photosensitizer, where photoinduced electron transfer generates the DCA radical anion, which upon further excitation triggers reductive dehalogenations and detosylations. Our study provides the proof-of-concept for controlling the outcome of a red-light driven biphotonic reaction by altering the photosensitizer, and this seems relevant in the greater context of tailoring photochemical reactivities.

Graphical abstract: Sensitizer-controlled photochemical reactivity via upconversion of red light

Supplementary files

Article information

Article type
Edge Article
Submitted
20 sep 2022
Accepted
21 nov 2022
First published
01 dec 2022
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2023,14, 149-161

Sensitizer-controlled photochemical reactivity via upconversion of red light

F. Glaser and O. S. Wenger, Chem. Sci., 2023, 14, 149 DOI: 10.1039/D2SC05229F

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