All-Red-Light Photoswitching of Indirubin Controlled by Supramolecular Interactions

Abstract

Red light responsiveness of photoswitches is a highly desired property for many important application areas such as biology or material sciences. The main approach to elicit this property uses strategic substitution of long known photoswitch motives such as azobenzenes or diarylethenes. Only very few photoswitches possess inherent red-light absorption of their core chromophore structures. Here we present a strategy to convert the long known purple indirubin dye into a prolific red light responsive photoswitch. In a supramolecular approach its photochromism can be changed from a negative to a positive one while at the same time significantly higher yields of the metastable E isomer are obtained. E to Z photoisomerization can then also be induced by red light of longer wavelengths. Indirubin therefore represents a unique example of reversible photoswitching using entirely red light for both switching directions.

Fourfold Double-Bond Substituted Hemiindigo: Highly Functionalized Red-Light Responsive Photoswitches

“…Progress like this is inevitably tied to advances at the fundamental level and consequentially new molecular photoswitch classes, 21 new modes of geometry changes, new modes of electronic alterations, and new types of photoreactions have been discovered. Recent examples are modified azobenzene, [22][23][24][25][26][27][28][29] hydrazone-, 30 Stenhouse dye-, imidazolyl-radical-, 31 or indigoid photoswitches, [32][33][34][35][36][37] each of which offering unique advantages. Our group has investigated indigoid chromophores intensively and transformed many of long known dyes in this class into capable photoswitching motives.…”