Bistable Photoswitching of Hemithioindigo with Green and Red Light: Entry Point to Advanced Molecular Digital Information Processing

Abstract

Photoswitches reacting to visible light instead of harmful UV irradiation are of very high interest due to the mild and broadly compatible conditions of their operation. Shifting the absorption into the red region of the electromagnetic spectrum usually comes at the cost of losing thermal stability of the metastable state-the switch switches off by itself. Only recently have photoswitches become available that combine visible light responsiveness with high bistability. However, shifting the wavelengths for bistable photoswitching beyond 600 nm is still a great challenge without involving secondary processes such as two-photon absorption or sensitization. We present a simple hemithioindigo photoswitch that can efficiently be photoisomerized using green and red light while maintaining a high thermal barrier of the metastable state. This highly sought after properties allow for selective switching in a mixture of hemithioindigo dyes. In addition, protonation can be used as second independent input altering the light response of the switch and allowing construction of advanced molecular digital information processing devices. This is demonstrated by realizing a broad variety of logical operations covering combinational and sequential logic behavior. By making use of the protonation-induced loss of thermal bistability, a high security keypad lock could be realized, which distinguishes the sequences of three different inputs and additionally erases its unlocked state after a short time.

Photocontrol of Drug Release from Supramolecular Hydrogels with Green Light

“…Daylight irradiation resulted in a decrease of the trans ‐isomer ratio in the material. These properties are consistent with previous reports on fluorinated azobenzene derivatives …”

Hemithioindigos for Cellular Photopharmacology: Desymmetrised Molecular Switch Scaffolds Enabling Design Control over the Isomer‐Dependency of Potent Antimitotic Bioactivity

“…Towards more general photopharmaceutical applications of HTIs, it is noteworthy that the metastable isomers of HTIs bearing mesomerically stabilising or tautomerisable substituents in para on the hemistilbene are not necessarily “fast‐relaxing” (half‐lives below ∼1 ms) in aqueous environments, unlike what is seen for azobenzenes (probably the same is true on all positions of the thioindoxyl, explorations are ongoing by other groups). Azobenzenes face other common challenges in cellular environments, including thiol addition into the photoswitchable N=N double bond that can lead to compound degradation, sequestration, or off‐target effects; we expect that the C=C photoswitchable bond in HTIs will have a different and overall diminished profile of thiol sensitivity.…”

Recent Implementations of Molecular Photoswitches into Smart Materials and Biological Systems

“…HTI (Figure c) is another stilbene‐type switch generated by condensation of benzothiophenones with aldehydes or, especially for sterically hindered systems, by condensations and cyclizations to yield the heterocyclic system in situ . By appending HTI with strongly donating substituents or a pyrrole system, a bathochromic shift was achieved that enabled switching with green, red, or even IR light with lifetimes of the photoisomers on the scale of days.…”

“…More recent applications include digital information processing with a pH‐sensitive HTI molecule; a visible‐light‐responsive supramolecular receptor (HTI tweezers), the folding and affinity for aromatic guest molecules of which can be altered by irradiation and heating, or even light‐driven relocation of the guest between two such receptors …”