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.