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An “inverse” photo-chromism (photo-decolourization) has been found in the case of indolinospiropyranes having an electron donating substituent in 6′- and any other type of substituent in 8′-position in polar solvents and polymeric matrices. The quantum yield of the photo-decolourization in visible light has been found to increase with the spiropyrane content. Rapid spectroscopy confirmed the existence of a pigmented form in a photo-excitation of stereo-isomers.

1. Irradiation of acetone solutions of spiropyrans with an OCH3 substituent in the 8' position leads to the formation of a stable colored form. The absorption band for this form appears only in the spectra of ketone solutions. 2. The formation this stable colored form proceeds with the absorption of light by an intermediate spiropyran form, the quantum yield for this process being 0.14.

1. We have measured the energy barriers to conversion of the colorless form of five indolinospiropyrans with different 8′-substituents. 2. We have measured the dependence of the angle between the oscillators of the electronic transitions of the colored form of the spiropyrans on the donor-acceptor properties of these substituents. 3. The introduction of substituents into the pyran fragment of the spiropyran molecule controls the pathway for the color reaction and the equilibrium among the stereoisomers of the colored form.

1. 1-(β-Hydroxyrethyl)-3,3-dimethyl-6'-nitrospiro(indoline-2,2'-[2H-1]benzopyran)s (II) substituted by an electron-accepting group (Br, NO2) in position 8' exist in solution mainly in the ring-opened merocyanine form. The equilibrium constant (Ke) is two orders of magnitude greater than that of unsubstituted (II). 2. Compound (II) with an OCH3 group exists as two isomers in solution; Ke is solvent-dependent. 3. We have developed a procedure for the synthesis of 1-(β-methacryloylhydroxyethyl)-3,3-dimethyl-6'-nitro-8'-bromo(8'-methoxy)spiro (indoline-2,2'-[2H-1]benzopyran).