Synthesis, characterization, and solvent-independent photochromism of spironaphthooxazine dimers

Specifically angled, conjugated spiroindolinonaphthooxazine dimers (SNOD) have been synthesized. The photochromic reactions of two types of SNOD were studied under continuous UV irradiation in solvents of different polarity. Comparison of these results with the single unit provides the examination of the specific effect of substituents on their photochromic properties and relaxation kinetics. The photomerocyanine isomers showed positive solvatochromism, supporting the premise for a less polar quinoidal structure. The thermal closing rate at 25 °C ranged from 0.2 to 1.6 s−1 depending on the compound and solvent. Photochromism of these new compounds showed little dependency on solvent polarity and stable cyclability.

► Uniquely shaped bi-photochromes have been synthesized.
► Two spironaphthooxazine dimers exhibit positive solvatochromism.
► SP-MC photochromism shows fatigue resistant and excellent cyclability.
► Thermal closing rates are relatively constant and independent to the solvent polarity.