Photo‐ and thermochromic cation sensitive spiro[indoline‐pyridobenzopyrans]

The photo‐ and thermochromic behaviour of a series of spiro[indolinepyridobenzopyrans] 1–5 has been studied. The thermodynamic and kinetic parameters of the thermal equilibria between the ring‐closed and ring‐opened (merocyanine) isomeric forms of spiropyrans have been determined using UV–Vis absorption and 1 H NMR spectroscopies techniques. The most stable form of 1‐(2‐hydroxyethyl)‐spiro[indoline‐pyridobenzopyran] 4 is represented by its trans ‐(hydroxystyryl)oxazolidineindoline isomer coexisting in acetone solution with the ring‐closed spiroform. In the presence in solution of metal salts, spiro[indoline‐pyridobenzopyrans] exhibit strong ionochromic effect due to the formation of complexes with the merocyanine ligand. The composition of the complexes formed by Zn 2+ and Ni 2+ ions has been determined with the use of spectrophotometric and electrospray ionisation mass spectroscopy techniques. The stepwise stability constants and spectral properties of the most stable 1:1 and 1:2 metal/merocyanine complexes have been determined. Selectivity of the complexation reaction depends on the position of the thermochromic equilibrium. Copyright © 2007 John Wiley & Sons, Ltd.