Molecular platform for photochromic balance based on spiro[indoline-pyranoquinolines]

Molecular platforms, capable of exhibiting various well-known properties, allow us to observe under certain structural modifications, due to the combination of these properties, the formation of new effects or phenomena, for example, photochromic balance. The 6-bromo-substituted spiro[indoline-pyranoquinolines] were found to exhibit the properties of photochromic balance, exhibiting both positive and negative T-type photochromism. A detailed study was carried out on the thermodynamics and kinetics of processes, the combination of which forms the effect of photochromic scales: the equilibrium of cyclic and merocyanine isomers of spiropyrans, thermal opening of the pyran ring and thermal recyclisation, and photocolouring and photobleaching of spiropyran solutions. Based on experimental data and quantum chemical modelling, directions for structural tuning have been established for the most pronounced manifestation of the effect of photochromic balances based on spiro[indoline-pyranoquinolines], which include enhancing the electron-withdrawing properties of the substituents in the pyridobenzopyran part of spiropyrans and the introduction of strong electron-donating groups into the indoline fragment.