Azobenzene Photoswitching with Near-Infrared Light Mediated by Molecular Oxygen

Abstract

Efficient photoisomerization between the cis and the trans states of azobenzenes using low-energy light is desirable for a range of applications in, e.g., photobiology yet challenging to accomplish directly with modified azobenzenes. Herein, we utilize molecular iodine as a photocatalyst to induce indirect cis-to-trans isomerization of 4,4′-dimethoxyazobenzene with 770 nm nearinfrared light, showing robustness during more than 1000 cycles in ambient conditions. Intriguingly, the catalysis is mediated by molecular oxygen, and we demonstrate that other singlet-oxygengenerating photosensitizers besides iodine, i.e., palladium phthalocyanine, catalyze the isomerization as well. Thus, we envision that the approach can be further improved by employing other catalysts with suitable photoelectrochemical properties. Further studies are needed to explore the applicability of the approach with other azobenzene derivatives.

Singlet Oxygen's Potential Role as aNonoxidativeFacilitator of Disulfide S–S Bond Rotation†

“…Just as fascinating to us is the possibility that torsional flexibility could offer antiphotooxidant activity by converting excitedstate 1 O 2 to ground-state 3 O 2 by means of a conformational energy-releasing process. Intriguingly, this process has been seen in azobenzene (64). Finally, it should be noted that other reagents, such as protons, should be explored as candidates that might also facilitate rotations of S-S bonds.…”

Efficient iron-catalyzed direct acylation of amines with carboxylic acids and esters under oxygenated conditions

“…Several reports have shown the beneficial effect of molecular oxygen in reactions not directly related to classical oxidation processes, like the molecular oxygen-induced activation of certain bonds, 21 of molybdenum-based Lewis acids 22 and of gold catalysts. 23 In addition, activation by dioxygen has resulted to be essential for certain challenging reactions such as skeletal rearrangements 24 photoisomerization between the cis and the trans states of azobenzenes 25 and other oxygen-driven photoisomerization reactions of alkenes and polyenes, 26 redox-neutral nucleophilic aromatic substitutions leading to seven-membered ring formation, 27 conversion of pincer metal complexes into metallabenzenes, 28 and iron-catalyzed dearomatization of 2-naphthols. 29 Accordingly, we decided to investigate the influence of dioxygen on iron-catalyzed amidation.…”

Red-light photoswitching of indigos in polymer thin films

“…9,12,34,35 To this end, progress has been made by (i) changing the electronic properties of conventional photoswitches such as azobenzenes through structural changes, [36][37][38][39][40][41] (ii) designing new photoswitchable scaffolds and structures that intrinsically absorb low-energy light, 25,[42][43][44] and (iii) exploiting indirect isomerisation using photocatalysts. [45][46][47] Yet, the vast majority of these investigations has been restricted to solution, and switching with red or near-infrared light in solid matrices has remained largely unexplored. 48,49 With its long history in providing blue colour, indigo is nowadays one of the most widely used dyes (Scheme 1).…”