Kinetics of photochromic reactions in a 10-membered dibenzoazo crown ether

Abstract

The paper reports on results of measurements of the kinetics of the photochromic reaction in a member of the series of azobenzene-containing crown ethers. The 10-member crown (referred to as O2N2) undergoes a reversible photo- and thermally driven isomerisation, similarly as parent azobenzene. It is expected that constraints imposed by the crown on conformations of azobenzene-containing crown ethers may modify the energetics of the isomerisation process. The experiments were performed in pMMA matrices. The isomerisation was monitored spectrophotometrically. The trans – cis isomerisation was driven photochemically ( λ =365 or 500 nm) and the reverse cis – trans isomerisation was driven by the excitation in the visible (413 nm) or occurred spontaneously in the dark. The pre-exponential factor of the latter process amounts to ca. 6×10 11 s −1 and the activation energy is equal to ca. 118 kJ/mol, being higher than in other azobenzene-containing crown ethers and in parent azobenzene. The stability of the cis isomer at room temperature is much higher than that in other crown ethers, the extrapolated ambient-temperature time constant being of the order of several years. The stability of the cis form of O2N2 in the darkness, combined with a good reversibility is a promising feature for future applications of the material in optical data storage.