Novel photochromic indolinospiropyrans of coumarin series with high level of colorability

•Novel indolinospiropyrans containing coumarin moiety annulated to the 2H-pyran ring were synthesized.•The obtained compounds are characterized by exceptionally high values of colorability (the product of a quantum yield of photocoloration and molar absorption coefficient of the photoinduced form).•Both strong electron donating and electron withdrawing substituents in the indoline moiety provide for the noticeable decrease of colorability.•Merocyanine isomers of the obtained compounds show negative solvatochromism characteristic of dipolar structures, which was confirmed by the observed decrease in the rate constants of the thermal recyclisation reactions with the increase in the solvent polarity.

Indolinospiropyrans containing coumarin moiety annulated to the 2H-pyran ring at the 6,5-position exhibit positive photochromism under normal conditions and are characterized by exceptionally high values of colorability. Both strong electron donating and electron withdrawing 5-R substituents in the indoline moiety provide for the noticeable decrease of colorability. Negative solvatochromism of merocyanine isomers of the synthesized spiropyrans indicates their dipolar structure which is manifested by the reduction of the rate constants of recyclization upon increasing solvent polarity.

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