Engineering Supramolecular\n[<i>c</i>2]Daisy\nChains for Structural Hierarchy-Dependent Emission and Photoreactivity

Organic photofunctional materials exhibit properties\nthat are highly\ndependent on their structural hierarchy. The variability in intermolecular\ninteractions and molecular packing in both monomeric and aggregated\nstates complicates the controllability and predictability of their\nphotophysical and photochemical properties. To address this challenge,\nwe developed three luminescent supramolecular [<i>c</i>2]daisy\nchains as simplified models. The rigid and mutually embedded linkers\nbetween the host and guests facilitate the formation of [<i>c</i>2]daisy chains with balanced stability and dynamics. Additionally,\nthe close and tunable π–π interactions between\nthe luminescent units provide a structural basis for fluorescence\nmodulation and topochemical photoreactions. We performed two sets\nof comparisons to assess luminescence and photoreactivity: one comparison\ninvolves molecules with and without crown ethers, and the other contrasting\ntheir behavior under UV excitation in solution (diluted and concentrated)\nversus in the aggregated and crystalline states. Specifically, in\nthe crystalline state, [<i>c</i>2]daisy chains effectively\nstabilize molecular packing, leading to highly efficient dimer-dependent\nemission. This unique structure remains in both solution (<i>c</i> > 1 mM) and aggregated states, which can direct the\nreaction\npathway toward rapid and efficient intermolecular photocycloaddition\nupon UV irradiation. However, in highly diluted solution (10 μM),\n[<i>c</i>2]daisy chains dissociate into monomers, which\nfurther undergo intramolecular photocyclization. This study provides\nnew insights into employing supramolecular strategies for controllable\nmolecular aggregation and the fine-tuning of photoreaction pathways\nand kinetics.