Stabilization of thermally unstable photoisomers of pyridinium-functionalized hemithioindigo switches by host-guest complexation

Synthesis and Evaluation of the Photochemical Properties of Heterocyclic Hemiindigos

This study reports a series of novel heterocyclic hemiindigos (Het-HI) synthesized via the condensation of indoxyl acetate with various heteroaromatic aldehydes. The influence of electron-rich and electron-poor heterocycles on the photochemical and photophysical properties of these compounds has been investigated. Our findings reveal that several Het-HIs exhibit noteworthy photoswitching behavior, including enhanced absorption at the visible region. Notably, certain derivatives respond efficiently to green and red light, achieving good conversions to the metastable E-isomer and displaying prolonged half-lives of up to 53 days in a polar solvent. The results highlight the potential of these photoswitches for applications in molecular devices and responsive materials.

Easily Accessible Substituted Heterocyclic Hemithioindigos as Bistable Molecular Photoswitches

Thioaurone chromophores, part of the indigoid family and commonly named hemithioindigos, have recently gained attention due to their interesting photoswitching properties. The study focuses on heterocyclic hemithioindigos (Het-HTIs) and investigates their synthesis using electron-rich and electron-poor heterocycles and modifications to the thioindigo moiety. Furthermore, it aims to evaluate the photoswitching performances of these synthesised compounds, with a particular emphasis on the influence of the heterocycles on the photoisomerization capabilities, which was found to be more prominent than the modifications made to the thioindigo moiety. Among the 44 Het-HTIs tested, several exhibited highly efficient photoswitchable properties, demonstrating Z-to-E photoisomerization in the blue region, and E-to-Z photoisomerization in the green or the red regions. Additionally, the metastable E-isomer displayed an impressive half-life of up to 54 days in a polar solvent (DMSO). These results suggest that heterocyclic hemithioindigos hold great promise as photoswitches for researchers interested in light-controlled molecular mechanisms.

A concise synthesis of thioaurones via NBS-induced cyclization of MOM-protected 2'-mercaptochalcones

A mild and efficient approach for the synthesis of thioaurones via NBS-induced cyclization of methoxymethyl-protected mercapto-chalcones has been developed. This simple method is highly functional group tolerant and provides straightforward access to thioaurones in good to high yields.

Heterocyclic Hemithioindigos: Highly Advantageous Properties as Molecular Photoswitches

A survey of heterocyclic hemithioindigo photoswitches is presented identifying a number of structural motives with outstanding property profiles. The highly sought-after combination of pronounced color change, quantitative switching in both directions, exceptional high quantum yields, and tunable high thermal stability of metastable states can be realized with 4-imidazole, 2-pyrrole, and 3-indole-based derivatives. In the former, an unusual preorganization using isomer selective chalcogen- and hydrogen bonding allows to precisely control geometry changes and tautomerism upon switching. Heterocyclic hemithioindigos thus represent highly promising photoswitches with advanced capabilities that will be of great value to anyone interested in establishing defined and reversible control at the molecular level.