Diarylethene Photoswitches Undergoing 6π Azaelectrocyclic Reaction: Disrotatory Thermal Cycloreversion of the Closed-Ring Isomer

Hamatani, Shota; Kitagawa, Daichi; Kobatake, Seiya

doi:10.1021/acs.jpclett.3c02207

Cited by 7 publications

(4 citation statements)

References 25 publications

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“…Unexpectedly, we did not observe the photoproduct of a classical 6-π-electrocyclic diarylethene reaction, which was recently reported to take place in thiazole-diarylethene. 37 Instead, irradiation leads to the electrocyclic formation of a positively charged aromatic pyrido[1,2-a]pyrimidin-5-ium ring in conjunction with reversible C−S bond breaking and ring opening of the adjacent thiophene. Overall, a zwitterionic thiolate species is obtained in up to 94% yield (Figures 1a and 2a,b), which is colored and shows rare negative solvatochromism, typical for charged ground state species.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Open 1 possesses absorption in the UV range and therefore was irradiated with 285 nm or 365 nm light (Figure ). Unexpectedly, we did not observe the photoproduct of a classical 6-π-electrocyclic diarylethene reaction, which was recently reported to take place in thiazole-diarylethene . Instead, irradiation leads to the electrocyclic formation of a positively charged aromatic pyrido[1,2- a ]pyrimidin-5-ium ring in conjunction with reversible C–S bond breaking and ring opening of the adjacent thiophene.…”

Section: Resultsmentioning

confidence: 99%

“…To our surprise, however, no investigations had been made to examine the possibility of forming and breaking CN bonds during the electrocyclic photoreaction in diarylethenes when we started this investigation. Just very recently, the group of Kobatake has published the reversible C–N single bond formation in a two-state aza-diarylethene photoswitch, similar to the C–C bond electrocyclization reactions observed in the parent compound …”

Section: Introductionmentioning

confidence: 99%

“…Just very recently, the group of Kobatake has published the reversible C−N single bond formation in a two-state aza-diarylethene photoswitch, similar to the C−C bond electrocyclization reactions observed in the parent compound. 37 In this work, we disseminate the reversible C�N double bond formation and breaking within a pyrimidine-substituted four-state aza-diarylethene photoswitch, which proceeds via concomitant thiophene-ring opening and formation of an aromatized zwitterionic metastable state. The metastable state is strongly colored and fully reverts back to the colorless open ring aza-diarylethene.…”

Section: ■ Introductionmentioning

confidence: 99%

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Reversible C═N Bond Formation Controls Charge-Separation in an Aza-Diarylethene Photoswitch

Sacherer,

Gracheva,

Maid

et al. 2024

J. Am. Chem. Soc.

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Diarylethenes belong to the most eminent photoswitches and have been studied for many decades. They are found in virtually every field of application and have become highly valuable molecular tools for instilling light-responsiveness into materials, catalysts, biological systems, or pharmacology. In this work, we present a novel and distinct type of pyrimidine-based aza-diarylethene, which undergoes a highly unusual zwitterion-forming photoreaction. During this fully reversible process, a CN double bond is established under concomitant aromatization and thiophene-ring opening. The metastable zwitterion thus possesses a positively charged extended aromatic structure and an independent conjugated thiolate function. It can further photoisomerize between a more stable Z and a less stable E isomer, resulting in effective four-state photoswitching. Unusual for diarylethenes, the metastable isomers show negative solvatochromism and red-shifted absorption in apolar solvents. With this behavior, aza-diarylethenes effectively bridge the properties of merocyanines and diarylethenes. Thermal stability of the zwitterions can be modulated from very labile to highly stable behavior in response to pH, again in a fully reversible manner. Pyrimidine-based aza-diarylethene thus establishes a unique photoreaction mechanism for diarylethenes, allowing control of charge separation, thermal stability, and color generation in a different way than hitherto possible.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reversible C═N Bond Formation Controls Charge-Separation in an Aza-Diarylethene Photoswitch

Sacherer,

Gracheva,

Maid

et al. 2024

J. Am. Chem. Soc.

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Beyond Photochromism: Alternative Stimuli to Trigger Diarylethenes Switching

Ai,

Lan,

et al. 2024

Advanced Science

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Diarylethenes (DAEs) are typical photochemically reversible type (P‐type) photochromic materials with excellent thermal stability and high fatigue resistance and are widely exploited as photo‐switches for various applications in molecular devices, data storage, photoresponsive materials, and bioimaging, etc. In recent years, there is an increasing number of reports using heat, acid, electrochemistry, etc. to drive the isomerization reaction of DAEs. The response to two or more different stimuli enables multi‐functionality within a single DAE molecule, which would facilitate complex logic‐gate operations, multimode data storage, and increased information density. Herein, the recent advances in DAE systems utilizing stimuli “beyond photo” to trigger the isomerization processes from three perspectives: acidochromism, thermochromism, and electrochromism are reviewed. Emphasis is placed on the molecule design strategies and the underlying mechanisms for cyclization and cycloreversion processes addressed by the alternative stimulus. Then the noticeable applications made in multi‐stimuli responsive DAE systems are summarized. Additionally, the challenges and opportunities of DAE switches driven by stimuli “beyond photo” in the future are also discussed.

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Aza‐Diarylethenes Undergoing Both Photochemically and Thermally Reversible Electrocyclic Reactions

Hamatani,

Kitagawa,

Kobatake

2024

Angewandte Chemie

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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 a part of hexatriene structure 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 structure, which was well explained based on the reaction mechanism of photochemical and thermal ring‐closing reactions. These findings not only advance the field of aza‐diarylethenes but also inspire future research in the development of new photoswitches.

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Diarylethene Photoswitches Undergoing 6π Azaelectrocyclic Reaction: Disrotatory Thermal Cycloreversion of the Closed-Ring Isomer

Cited by 7 publications

References 25 publications

Reversible C═N Bond Formation Controls Charge-Separation in an Aza-Diarylethene Photoswitch

Reversible C═N Bond Formation Controls Charge-Separation in an Aza-Diarylethene Photoswitch

Beyond Photochromism: Alternative Stimuli to Trigger Diarylethenes Switching

Aza‐Diarylethenes Undergoing Both Photochemically and Thermally Reversible Electrocyclic Reactions

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