A Visible-Light-Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene

摘要

Ketal-substituted bridged azobenzenes have been synthesized; these display a symmetrical boat conformation with the ketal in pseudo-equatorial positions. These bridged Z-azobenzenes (Z(1)) readily photoisomerize to the E-isomer as well as another Z-conformer (Z(2)) with ketal function on the pseudo-axial position upon irradiation at 406 nm. The two diastereomeric conformers display distinct physicochemical characteristics. Spectroscopic and NMR investigations supported that interconversion of two conformers occurs via the E-isomer, with good photochemical quantum yield (Phi(Z1 -> E) = 0.45 +/- 0.03, Phi(E -> Z1) = 0.33 +/- 0.05, Phi(E -> Z2) = 0.37 +/- 0.06 and Phi(Z2 -> E) = 0.36 +/- 0.04). The system shows high photostability and no thermal equilibrium between the two stable Z(1) and Z(2) conformers.