The enantiomers of a racemic photoresponsive material represent two distinct states that can be modulated with irradiation at a single wavelength by changing the handedness of the light. Dynamic control over molecular chirality was obtained by the interconversion of enantiomers of helically shaped molecules with either left or right circular polarized light (CPL). Photoresolution of the bistable compound as a dopant in a nematic liquid crystalline phase by CPL irradiation led to a chiral mesoscopic phase. The chiral information inherent to CPL is therefore transmitted to the bistable molecule, followed by amplification and macroscopic expression of the chirality.

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Using thin films of a cholesteric mixture of acrylates 2 and 3 doped with the chiroptical molecular switch (M)‐trans‐1, photocontrol of the reflection color between red and green is possible. This doped liquid‐crystal (LC) film can be used for photoinduced writing, color reading, and photoinduced locking (via polymerization) of chiral, optically written information.

The control of chirality by optical molecular switches offers intriguing prospects in the design of new materials. For example, photochemically induced stilbene‐type cis‐trans isomerization of 1 (see Figure) results simultaneously in reversal of the helicity. The molecular design of switching units, the possibility of highly stereoselective optical molecular switching, and an approach to a gated response are described.

The fluorescence and chirality of photoswitchable inherently dissymmetric alkenes cis 1 and trans-2-nitro-7-dimethylamino-9-(2´,3´-dihydro-1´H-naphtho[2,1-b]thiopyran-1´-ylidene)-9H-thioxanthene 2 are reversibly modulated by irradiation whereas photoresponsive effects and emission are regulated by reversible protonation.