Electronic structure of merocyanine form of indolinespirobenzopyrans determined by electronic spectroscopy and dielectric measurements

Abstract
The permanent dipole moments of the merocyanine form of four indolinespirobenzopyrans in the ground (µg) and first excited states (µe) were determined by electronic spectroscopy and dielectric measurements. The high value of µg(11.8–13.3 D) indicates strong intramolecular charge transfer from nitrogen to oxygen atoms and supports the zwitterionic structure of the merocyanine form. The values of µe are much less (3.5–5.1 D) in comparision with µg, showing that the electronic structure of the merocyanine form in the first excited singlet state is closer to a non-polar quinoid type structure.

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