Kinetic study of the fast thermal cis-to-trans isomerisation of para-, ortho- and poly-hydroxyazobenzenes

JAUME GARCIA-AMORÓS; ANTONI SÁNCHEZ-FERRERA; WALTER A. MASSAD; SANTI NONELL; DOLORES VELASCO

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2010 vol. 40 p. 13238 - 13242

1463-9076

The thermal cis-to-trans isomerisation process has been studied for a series of para-, ortho- and polyhydroxy-substituted azobenzenes in different solvents. The kinetics of the thermal back reaction for the p-hydroxy-substituted azobenzenes depend strongly on the nature of the solvent used, with relaxation times ranging from 200–300 milliseconds in ethanol to half an hour in toluene. Otherwise, the process rate is mainly independent of the solvent nature for the ortho substituted analogues. Polyhydroxy-substituted azobenzenes show very much faster kinetics than the para- and ortho- monohydroxyazoderivatives. With relaxation times of 6–12 milliseconds in ethanol, they are optimal molecules for designing fast optical switching devices. All the hydroxyazoderivatives thermally isomerise from the metastable cis form to the thermodynamically stable trans isomer through a rotational mechanism.