Arriving at Short Wavelength Infrared: Beyond 1000 nm Reversible Photoswitching of peri-Anthracenethioindigo Using Aggregation Induced Bathochromism

The development of modern molecular photoswitches has made tremendous progress with the advent of low-energy responsive variants able to use visible and red light for reversible photoresponses. Dedicated approaches have been developed to achieve such highly desired properties including push-pull substitution, new chromophore designs, and physical means such as two-photon absorptions, sensitization, or upconversion. However, reaching further into the near infrared (NIR) has proven to be extremely challenging so far, raising the question whether viable photoswitching can actually go beyond 1000 nm. Here we use the concept of aggregation induced bathochromism (AIB) to enable direct excitation beyond 1000 nm for reversible photoswitching. Derivatives of the recently reported peri-anthracenethioindigo (PAT) can be aggregated into ca. 500 nm large particles, which shifts their absorption far beyond 1000 nm and into the short wavelength infrared (SWIR) region. Upon irradiation with 1020 nm light, the metastable Z isomer is obtained while at the same time the aggregates are dissolved. Photoisomerization of the Z isomer with orange or red light allows to return to the aggregated state establishing reversible beyond 1000 nm photoswitching. Further, a secondary and independent level of control is enabled via pH-dependent aggregation and deaggregation and corresponding absorption shifting. The resulting multi-stimuli responsiveness was applied in advanced molecular logic operations in the red and NIR absorption regime. AIB thus offers a highly promising way to realize extremely low-energy responsive photoswitching while at the same time allowing to control aggregation and dissolution behavior at the SWIR end of the electromagnetic spectrum.