Cucurbituril-Mediated Stacking Mode Conversion of Noncovalent Dimer

The precise control of the spatial arrangement of organic photoconductive molecules plays an essential role in the fields of optoelectronics and bio-imaging. Herein, three rigid diphenylpyridine substituted toluene derivatives p-BPy, m-BPy, o-BPy with angles of 180, 120 and 60 degrees, are synthesized, respectively. The crystal structures reveal that both p-BPy and m-BPy are J-aggregate mode, and m-BPy stacks in an antiparallel manner, while p-BPy is in the isotropically parallel. 2D nuclear magnetic resonance (2D NMR) experiments demonstrate that p-BPy and m-BPy still are J-aggregate mode in aqueous solution, and o-BPy does not stack. Cucurbit[8]uril (CB[8]) can bind two p-BPy or m-BPy molecules expectedly in its cavity, and the former still is J-aggregate like in the solid state and aqueous solution with fluorescence emission peak red-shifts from 490 to 570 nm. Surprisingly, the stacking pattern of two m-BPy molecules in the CB[8] cavity changes from antiparallel to isotropic, resulting in excimer emission with a quantum yield increases significantly from 26.6% to 97.1%. This observation suggests that the cavity of CB[8] can mediate the stacking mode conversion of the noncovalent dimer m-BPy, and could be useful for the design of organic photoconductive molecules in the future.