A Reversible 900 nm Near-Infrared Photoswitch for Invisibly Writable 2D and 3D Displays.

Molecular photoswitches interchange between different states in response to light irradiation and represent prominent tools to deliberately control changes at the smallest scales. A standing challenge for their development is pushing absorptions into the low-energy end of the electromagnetic spectrum, which is highly desirable to avoid photodamage, allows mixing of photoresponsive components, and maximizes the available color range. Here we report on a novel photoswitch motif, peri-benzo[a]fluoranthenethioindigo (PBFT), enabling direct excitation with near-infrared (NIR) light up to 900 nm wavelengths in a fully reversible fashion. PBFT provides an outstanding property profile with high isomer yields, good thermal bistability, and strongly distinct color changes from pale green to deep blue. Application within a commercially available and easy-to-use polymer material allows to realize reversible and spatially resolved inscription of information with extremely long wavelengths of light. Writing information into versatile handheld 2D and 3D optical displays and optical memories is thus possible with non-damaging irradiation, invisible to the naked eye.