Cyclobis(paraquat-p-phenylene), also known as Blue Box, has drawn great attention in supramolecular chemistry on account of its cavity size which is suitable to host planar guest molecules paving the way for its implementation in mechanically interlocked molecular architectures. In view of non-covalent interactions, recognition motifs of this system have often been related to electrostatic interactions between π-electron deficient and π-electron rich units. This has significantly been leveraged through follow-up studies revealing that the radical form of this cyclophane is prone to undergo trisradical tricationic complexation with viologen radical cations and face-to-face radical pimerization between the outer spheres. The consistency in its recognition behaviors and self-organization in the solid states has enabled to make predictions to an assessable extent for designing larger supramolecular systems. On these grounds, deviations from these observations by its simple molecular modification have significant implications in respect of its utilization in this field. Herein, we present cyclobis(paraquat-p-2,5-dimethoxy phenylene) (1) which possesses methoxy-substituted pillars imbuing it with altered binding behaviors, unexpected solid-state structures and stereochemical properties. Although binding with neutral guests were found to be on a par with Blue Box, binding of its corresponding radical (2) with methyl viologen radical cation, forming the trisradical tricationic complex (3), is significantly weakened when compared with its pristine analog. In the superstructures of 2 and 3, the radical-radical interactions between these systems differ from those typically observed in Blue Box and derivatives. According to 1H NMR studies of 1, the sterical hindrance introduced by methoxy groups decreases the rotation of its pillars giving rise to two possible isomers with C2h and D2 symmetry. Our results show that the recognition behaviors of viologen incorporating cyclophanes can be effectively tuned by simple modification of its pillars, in particular, in their radical configuration.

Outfitting ‘Blue Box’ with short-side arms tunes radical-radical interactions

256th National Meeting (2018)

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