Dibenzo[b,f][1,4,5]chalcogenadiazepine Photoswitches: Conversion of Excitation Energy into Ring Strain

Tetra-ortho-substituted, heteroaryl and cyclic azobenzenes have emerged as three key strategies on morphology design of photoswitch to diversify controllability. Cyclic azobenzene is of particular utilization in photo-energy conversion due to rigid and ring-strain structure. Despite the well-recognized diazocine, the photo-switching properties of seven-membered cyclic azobenzenes (diazepines) have yet been exploited. Herein, we report a family of dibenzo[b,f][1,4,5]chalcogenadiazepines (DBChDs) and their T-type photo-switching nature with tunable relaxation rate. Based on experiments together with DFT calculations, we found that an unsymmetric 2-bithiophenyl-dibenzo[b,f][1,4,5]thiadiazepine exhibited an efficient response to 445 nm laser stimulation (quantum efficiency, phi(Z -> E)=0.71) with millisecond relaxation half-life (t(1/2)=40 ms). Photo-energy transduction efficiency was also exceptionally high with 29.1 % converted into ring-strain energy mainly loaded on azo pi-bond.

Automated summary

Three strategies, including tetra-ortho-substituted, heteroaryl, and cyclic azobenzenes, have been used to design the morphology of photoswitches for increased controllability. In this study, a family of dibenzo[b,f][1,4,5]chalcogenadiazepines (DBChDs) with tunable relaxation rates were reported. An unsymmetric 2-bithiophenyl-dibenzo[b,f][1,4,5]thiadiazepine showed efficient photo-switching properties in response to 445 nm laser stimulation.