Remarkable Role of C-I center dot center dot center dot N Halogen Bonding in Thixotropic `Halo'gel Formation

Halogen-bonding-induced self-assembly in the solution of equimolar mixtures of certain pyridyl-ended oligo p-phenylenevinylene (OPV)-derivatives with 1,4-diiodotetra-fluorobenzene is reported. The mode of self-assembly, that is, cocrystallization, thixotropic gelation, or precipitation, depends strongly on the nature of chains (n-alkyl chains as a function of length or short oxyethylene chain) appended to the OPV-backbone as well as on the cooling rate of the corresponding hot solution. Single-crystal X-ray diffraction studies of the cocrystals reveal the ``infinite'' chain formation via C-I center dot center dot center dot N halogen-bonding interactions between the two components. In addition, multiple noncovalent interactions induce cross-links among these halogen-bonded ``infinite'' chains. Interestingly, the molecular packing in the ``Cogel'' bearing OPV-derivative with oxyethylene chains is found to be very similar to that of the cocrystal of the same