Experimental investigation shows altered geometry influences solvation dynamics in cationic nanocages, suggesting shape is critical for photochemical reactivity.
Understanding how nanoconfinement geometry modulates solvent dynamics is critical for controlling the photochemical reactivity inside supramolecular hosts. Here, we investigate how altering the shape of a cationic metal-organic nanocavity from an octahedral-shaped full-cage to a square-pyramidal-shaped half-cage influences the nonequilibrium solvation dynamics around photoexcited host-guest charge-transfer (H-G CT) states in water. Femtosecond broadband transient absorption spectroscopy reveals that photoexcitation of the host-guest CT complex formed by entrapment of aromatic aldehydes inside both the full-cage and half-cage produces highly dipolar states, which relax via water-reorientation around the whole complex. The octahedral-shaped full-cage exhibits rapid solvation with an average time scale of ∼4 ps, whereas the square-pyramidal-shaped half-cage displays markedly slower solvation with an average time scale of ∼40 ps. This pronounced modulation is attributed to geometry-induced restriction of solvent access, host-guest complex population heterogeneity, and enhanced hydrophobic shielding within the half cage, establishing nanocavity shape as one of the critical parameters for tuning solvent-mediated excited-state stabilization in water-soluble nanocages.
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Yadav et al. (2026) studied this question.
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