Remarkable Role of C–I···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-diiodotetrafluorobenzene
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···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.