Abstract

An approximate method is put forward allowing one to extract information on the parameters determining rate constants (activation energies and frequency factors) from non-isothermal measurements of quantities proportional to the concentrations of reactants (e.g., absorbance). The method, based on an approximate solution of a first-order kinetic equation in a non-isothermal regime, has been extended to fractional-heating experiments—a technique often used to extract parameters of the distributions of rate constants. The method was employed to obtain information on the parameters controlling the thermally driven cis–trans isomerisation of a novel photochromic azobenzene derivative: azobenzene-containing crown ether dissolved in a polystyrene matrix. The kinetics of the thermal isomerisation is controlled by a distribution of rate constants, with the activation energy amounting to ca. 97 kJ mol⁻¹ and the frequency factor of the order of 10¹⁰ s⁻¹ The results obtained are in a good agreement with results of isothermal experiments performed on similar systems.