Efficient Conversion of Light to Chemical Energy: Directional, Chiral Photoswitches with Very High Quantum Yields.

Photochromic systems have been used to achieve a number of engineering functions such as light energy conversion, molecular motors, pumps, actuators, and sensors. Key to p rac tical applications is a high efficiency in conversion of light to chemical energy, a rigid structure for the trans mission of force to the environment and directed motion during isomerization. We present a novel type of photochromic system (diindane diazocines), that converts visible light with an efficiency of 18% to chemical energy. Quantum yields are exceptionally high with >70% for the cis-trans isomerization and 90% for the back-reaction and thus higher than the biochemical system rhodopsin (64%). Two diastereomers ( meso and rac emate) were obtained in only two steps in high yields. Both isomers are directional switches with high conversion rates (76-99%). No fatigue was observed after several thousands of switching cycles in both systems.