Aza-Diarylethenes Undergoing Both Photochemically and Thermally Reversible Electrocyclic Reactions

10 July 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Exploring novel molecular photoswitches plays a crucial role in the field of photo-functional materials chemistry. In this study, we synthesized aza-diarylethenes with benzothiophene-S,S-dioxide as an aryl group and investigated their photochromic properties. Unlike previously reported aza-diarylethenes, which exhibit fast thermally reversible photochromism, the compounds synthesized here exhibited pseudo-photochemically reversible photochromism. Due to their thermal stability, we successfully isolated the colored isomer. X-ray crystallographic analysis revealed for the first time that the colored isomer adopts a closed-ring structure with a bond between carbon and nitrogen atoms. Remarkably, these aza-diarylethenes exhibited not only photochemical ring-closing and ring-opening reactions but also thermal ring-closing and ring-opening reactions, driven by a thermal equilibrium between the open- and closed-ring isomers. This behavior, unprecedented for common diarylethenes, was elucidated through kinetic analysis, revealing an energy-level diagram for the thermal equilibrium between these isomers. Furthermore, 1H NMR spectroscopy revealed that both photochemically and thermally generated closed-ring isomers adopt the same molecular conformation. These findings not only advance the field of aza-diarylethenes but also inspire future research in the development of new photoswitches.

Keywords

aza-diarylethene
6π azaelectrocyclic reaction
Photochemically reversible
Thermally reversible
kinetic analysis

Supplementary materials

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Supporting Information
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Experimental details of syntheses, X-ray crystallographic data, determination of the photochromic reaction quantum yields, analyses of thermal ring-closing and ring-opening reactions.
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Movie S1
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Associated with Figure 7.
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CIF file for 3o
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CIF file for 3o
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CIF file for 3c
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CIF file for 3c
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CIF file for 4o
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CIF file for 4o
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CIF file for 4c
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CIF file for 4c
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Comment number 1, Liudmil Antonov: Jul 23, 2024, 15:02

Excellent work!