Near Infrared Photoswitching by Direct Excitation-A Next Frontier.

The field of molecular photoswitches has grown tremendously over the past decades and pervaded every applied field from chemistry, biology, physics, to materials science and beyond. A main driver for continuous progress is tailoring absorption properties as a fundamental tool for controlling the light response. So far, the shift of absorption from UV light addressability into lower-energy visible and red spectral regions has unlocked numerous unique opportunities, both in capability increase as well as in applicability of photoswitches. A next frontier has been opened more recently by extreme redshifting of absorption, allowing to enter the near-infrared (NIR) spectral realm via direct excitation. This minireview highlights these important developments, delineates design principles to achieve NIR responsiveness in molecular photoswitches, and showcases the specific benefits that come with such low-energy light control over molecular states. The outlook glimpses into the future and points out the particular opportunities and challenges ahead.