Modulation of Photoluminescence of BODIHY Dye Using Water‐Soluble Coordination Cages with Different Shapes

The confinement of guest molecules within supramolecular hosts can alter their photophysical properties. However, the role of the shapes of the hosts in regulating the guest‘s emission remains unexplored. Herein, we investigate how the shape of the host alters the emission behaviour of BODIHY (G1) dye encapsulated within two iso‐stoichiometric water‐soluble coordination cages: MC1 (Double‐Square Cage) and MC2 (Octahedral Cage). Encapsulation of G1 within MC1 results in a highly emissive solution, whereas similar confinement in MC2 leads to non‐emissive host‐guest solution. A similar trend was observed with different set of iso‐stoichiometric cages MC3 (Double‐Square Cage) and MC4 (Octahedral Cage). Using a combination of femtosecond transient absorption and time‐resolved florescence spectroscopy, we observed that the disparity in fluorescence behaviour of BODIHY is attributed to charge transfer interactions between the guest and ligand panels of cages. The shape of coordination cage dictating the preorganization of the guest within the cavity thereby supressing or promoting this charge transfer interactions. Moreover, we demonstrate a turn‐on emission of BODIHY dye due to its preferential binding to a double‐ square cage. These findings provide fundamental insights into host‐mediated modulation of guest’s photophysics and offers a blueprint for designing supramolecular systems with tuneable emissive behavior.