Quantitative investigations of cation complexationof photochromic 8-benzothiazole substituted benzopyran: towards metal-ion senensors

The photochromic, thermochromic and metallochromic behaviour of a series of three spiro[indoline-8-(benzothiazol-2-yl)-benzopyrans] has been investigated. The thermodynamic and kinetic parameters of their thermal equilibrium between the ring-closed (spiro) and ring-opened (merocyanine) isomeric forms have been determined using UV-Vis absorption and 1H NMR spectroscopies. By adding Co(II) and Ni(II) ions in acetonitrile solution, 1:1 and 1:2 metal:merocyanine complexes are formed simultaneously. Using appropriate numerical methods, the kinetic analysis of the complexation allowed us to determine accurately key thermodynamic and spectroscopic parameters of the metal complexes. Results showed that the complexation strength is very sensitive to the size of the indoline nitrogen substituent. Complexation can be reversed by shining white light on the coloured complexes which regenerates the inactive spiropyran form, and releases the metallic ion; hence, these systems display fully reversible negative photochromism. The Zn(II) complexes exhibit intense fluorescence in the 600–800 nm wavelength range. All these behaviours make these spiropyrans bearing benzothiazole heterocycles promising building blocks for the future construction of photodynamic chemosensors for transition metal ions

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