Substituent effects on the photochromic properties of 3,3-diphenyspiro[benzofluorenopyran-cyclopentaphenanthrene]s

• Naphthopyrans with electron-donating groups have been synthesized.
• Introduction of a methoxy group on C6 induced lengthening of the absorption bands.
• Methoxy groups on C4 of C3 phenyl groups induced faster decoloration.
• Additional methoxy group on C13 enhanced absorbance of the open form.
• As a result, a naphthopyran suitable for photochromic lenses was developed.

The introduction of electron-donating groups on the skeleton of a naphthopyran, 3,3-diphenyspiro[benzofluorenopyran-cyclopentaphenanthrene], has led to the development of a photochromic dye applicable to photochromic lenses. Introducing a methoxy group to C6 moved the absorption band of the MC form towards the longer wavelength. Further introduction of methoxy groups to the para-position of the phenyl groups on C3 induced faster decoloration of the MC form. Additional introduction of a methoxy group to C13 led to the enhancement of the absorption intensity as well as the facile, economic synthesis of the dye caused by the symmetrical property of the starting material.

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