Disequilibrating azoarenes by visible-light sensitization under confinement

03 March 2023, Version 1


The process of vision begins with the absorption of light by retinal, which triggers isomerization around a double bond and, consequently, a large conformational change in the surrounding protein opsin. However, certain organisms evolved different visual systems; for example, deep-sea fishes employ chlorophyll-like antennas capable of capturing red light and sensitizing the nearby retinal molecule via an energy-transfer process. Similar to retinal, most synthetic photochromic molecules, such as azobenzenes and spiropyrans, switch by double-bond isomerization. However, this reaction typically requires shortwavelength (ultraviolet) light, which severely limits the applicability of these molecules. Here, we introduce DisEquilibration by Sensitization under Confinement (DESC) – a supramolecular approach to switch various azoarenes from the E isomer to the metastable Z isomer using visible light of desired color, including red. DESC relies on a combination of a coordination cage and a photosensitizer (PS), which act together to bind and selectively sensitize E-azoarenes. After switching to the Z isomer, the azoarene loses its affinity to—and is expelled from—the cage, which can convert additional copies of E into Z. In this way, the cage⋅PS complex acts as a light-driven supramolecular machine, converting photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed via direct photoexcitation.


Coordination cages
Photoswitchable molecules
Host–guest complexes
Energy transfer

Supplementary materials

Supplementary Information
Materials and methods; Synthesis and characterization of cage C, azoarenes 1–9, and photosensitizers ps1–ps4 and TX; Synthesis and characterization of homodimeric inclusion complexes; X-ray data collection and structure refinement; Formation of azoarene·photosensitizer heterodimers and DisEquilibration by Sensitization under Confinement (DESC) studies; Transient fluorescence spectroscopy and quantum efficiency determination; Transient absorption spectroscopy (TAS); Quantum chemical calculations; Supplementary references


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