Kinetic modelling of the photochromism and metal complexation of a spiropyran dye: Application to the Co(II) – Spiroindoline-diphenyloxazolebenzopyran system

A spirobenzopyran containing 6-chloro and 8-diphenyloxazole substituents has been investigated in acetonitrile solution by nanosecond laser photolysis at room temperature. In degassed solution, a short-lived transient (5 μs) has been identified as the triplet state of the closed spiro form. The ratio between the singlet and triplet pathways of ring opening has been determined from oxygen quenching measurements. In the presence of Co(II), UV irradiation is needed to induce the complexation. The fast second order rate constant for the 1:1 complex formation has been determined. It is suggested that such kinetic parameter could be used to characterise the properties of metallochromic spiropyrans.