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 photochromism, quantitative switching in both directions, exceptional high quantum yields, and high thermal stability of metastable states can be realized with 4-imidazole 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 a next-generation of photoswitches with advanced capabilities that will be of great value to anyone interested in establishing defined and reversible control at the molecular level.