The enantiopurification of racemic mixtures of chiral molecules is important for a range of applications. Recent work has shown that chiral group-directed photoisomerization is a promising approach to enantioenrich racemic mixtures of BINOL, but increased control of the diasteriomeric excess (de) is necessary for its broad utility. Here we develop a cavity quantum electrodynamics (QED) generalization of time-dependent density functional theory and demonstrate computationally that strong light–matter coupling can alter the de of the chiral group-directed photoisomerization of BINOL. The relative orientation of the cavity mode polarization and the molecules in the cavity dictates the nature of the cavity interactions, which either enhance the de of the (R)-BINOL diasteriomer (from 17% to ≈40%) or invert the favorability to the (S)-BINOL derivative (to ≈34% de). The latter outcome is particularly remarkable because it indicates that the preference in diasteriomer can be influenced via orientational control, without changing the chirality of the directing group. We demonstrate that the observed effect stems from cavity-induced changes to the Kohn–Sham orbitals of the ground state.

Three Ln2+ 18-crown-6 complexes of the formula Ln­(18-crown-6)­I2 (Ln = Sm, Eu, Yb) were isolated from the explicit synthesis of the corresponding LnI2 salts with 18-crown-6 and tetrabutylammonium tetraphenylborate in organic media under air-free conditions. Each metal complex forms a distorted hexagonal bipyramidal geometry and crystallizes in the monoclinic space group P21/n. Comparatively, crystallization of Ln­(benzo-18-crown-6)­I2 (Ln = Sm, Eu, Yb) from the reaction of LnI2 with tetrabutylammonium tetraphenylborate and benzo-18-crown-6 in THF/ethanol under similarly air-free conditions yields two polymorphs. The first form, α, crystallizes in the monoclinic space group P21/c (or the nonstandard setting P21/n for α-Yb); whereas the second polymorph, β, crystallizes in P . While the geometries of the molecules only vary slightly, the molecular packing and intramolecular contacts are quite different. In the structure of β, π–π interactions between the benzo- moieties of adjacent molecules are observed, whereas these interactions are absent in α. Despite the similarities in these classically 4f n+1 lanthanide systems, the complexes display distinct spectroscopic features in their respective absorption and photoluminescence spectra. Broadband 5d → 4f photoluminescence was observed for the Sm and Eu compounds in the NIR region and UV–visible region, respectively. None of the three Yb compounds exhibit photoluminescence UV–visible-NIR region; however, a unique photooxidation event was observed resulting in characteristic Yb­(III) 4f → 4f transitions in the NIR region of the absorption spectra of these compounds. These findings are discussed along with structural comparisons of the 18-crown-6 and benzo-18-crown-6 compounds as well as other reported Ln­(II) crown complexes in the literature.

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Photoresponsive polymers, typically activated with direct excitation of an azobenzene moiety, are an intriguing class of materials for application as adaptive structures. Here, we introduce triplet excited state sensitization as a mechanism to harness light in a stilbene-based photopolymer (i.e., the carbon analogue of azobenzene). While the undoped film shows no response, the sensitized film exhibits polarization dependent bending under 445 nm irradiation via (1) sensitizer excitation, (2) triplet energy transfer, (3) stilbene isomerization, and (4) subunit reorientation. This work is the first to demonstrate stilbene-based photopolymers and triplet sensitization as a low energy light harvesting mechanism in photomechanics.

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