Contrasting binding modes and emission shifts of a single guest with cucurbitu[7]ril versus β-cyclodextrin

CB[7] and β-CD bind Si-4Ph-2Am guest in contrasting modes. • CB[7] binds cationic trimethylanilinium, forming nanorods with green emission. • β-CD encapsulates hydrophobic core, forming irregular aggregates with blue emission. In this work, the contrasting recognition behavior between a symmetric dicationic guest, 4,4′-(diphenylsilanediyl)bis(N,N,N-trimethylanilinium)diiodide (Si-4Ph-2Am) and two macrocycles (cucurbit[7]uril (CB[7]) and β-cyclodextrin (β-CD)) were investigated employing 1 H NMR, 13 C NMR, 29 Si NMR, 2D NOESY, and FT-IR, fluorescence spectroscopy, transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis. The results of 1 H NMR and 2D NOESY revealed that CB[7] encapsulates the two cationic trimethylanilinium groups via ion-dipole interactions, while, β-CD accommodates the central diphenylsilane unit through hydrophobic inclusion. The results of Job plot analyses indicate an host: guest stoichiometry of 1:2 for the CB[7] system and 2:1 for the β-CD system. The CB[7] directed complex assembles into uniform nanorods accompanied by a bathochromic emission shift from 460 nm to 512 nm. In contrast, the β-CD-directed complex remains as irregular aggregates with enhanced emission at 460 nm. This study establishes a powerful principle of host directed programming, wherein the choice of macrocycle influence the binding modes, stoichiometry, photophysical properties, and nanoscale assembly of multifunctional guest.