Spiropyran, chromene and spirooxazine, mélange á trois: Molecular logic systems through selective and reversible deactivation of photochromism mediated by CO2 gas

We report a new expanded molecular logic system based upon combinations of spiropyrans, spirooxazines and chromenes, whereby the photochromism of some molecules can be selectively preserved while reversibly deactivating the photochromism of others. The non-photochromic molecules can be reversibly activated by CO2 gas. It was found that the photochromic effect of spiropyrans, in general, and one spirooxazine (with a hydroxyl group on the naphtho-ring) could be reversibly deactivated by DBU, while a chromene and an unsubstituted spirooxazine remained photochromic in the system under the same conditions. The presence of protic solvent was necessary for the deactivation of some of these photochromic molecules and hence it was used as an additional sensitizer in the system. This afforded the expansion of stimuli for molecular logic operations and allowed combinations of the benign stimuli of UV, visible light, CO2, and CO2 depleted with protic and aprotic solvents. This effect provided the mechanism for molecular logic systems that do not suffer from the usual problems of dilution effects and hence become truly reversible. This is highly significant when designing molecular switches to perform logic operations.

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► Photochromic molecules were triggered with a combination of stimuli of visible light, UV, CO2 and N2.
► Multistimuli response photochromic systems were designed as reversible molecular switches.
► We have demonstrated a truly reversible molecular logic system that does not suffer dilution effects.
► Amidine deactivates the photochromism of some photochromic systems.
► CO2 was used as a trigger to reactivate the photochromism of spiropyran and spirooxazine with amidine.