Guest-Binding-Induced Interhetero Hosts Charge Transfer Crystallization: Selective Coloration of Commonly Used Organic Solvents

Unprecedented interheteromacrocyclic hosts charge transfer (CT) crystals were generated by cooling organic solutions containing p-dimethoxybenzene-constituted pillar5arene (P5A) and p-benzoquinone-constituted pillar5quinone (P5Q). Despite the weak CT interaction known between p-dimethoxybenzene and p-benzoquinone and the lack of formation of CT complexes between P5A and P5Q in the solution phase, CT cocrystals between P5A and P5Q were formed with solvent molecules included into the hosts' cavities. Such a cocrystallization arises from an elegant synergy between the CT interaction and solvent-binding-promoted crystallization. The interhetero hosts CT crystals were studied by optical and electron microscopic techniques, X-ray powder diffraction, solid-state NMR, UV–vis, IR spectroscopic studies, and X-ray single-crystal studies. The solvent complexation was critical for formation of the supramolecular CT microcrystals. The CT absorption bands faded upon removing the solvent molecules under vacuum, but they could be recovered by reuptake of the solvent molecules. Intriguingly, the CT absorption bands and uptake kinetics are distinguishably different for various organic solvents, thus providing a unique way to distinguish between different commonly used chemicals.