Hierarchical order in supramolecular assemblies of hydrogen-bonded oligo(p-phenylene vinylene)s

Mono- and bifunctional oligo(p-phenylene vinylene)s (OPVs) functionalized with ureido-s-triazine units have been synthesized and fully characterized. In chloroform monofunctional OPV derivatives dimerize with a dimerization constant of K-dim = (2.1 +/- 0.3) x 10(4) L/mol, while bifunctional OPV derivatives are present as random coil polymers in this solvent. In more apolar solvents such as dodecane, the hydrogen-bonded dimers of the monofunctional OPV derivative aggregate in chiral stacks, as can be concluded from UV/vis, fluorescence and CD spectroscopy. Temperature-dependent measurements show a first-order transition at 53 +/- 3 degreesC from the aggregated state to the molecularly dissolved phase. The bifunctional derivative also aggregates in dodecane; however, based on CD measurements, these aggregates are less: organized. This behavior is presumably the outcome of a competition between favorable pi-pi interactions and restricted conformational freedom, due to the hexyl spacer, which results in a frustrated supramolecular polymeric stack. The length of these polymers as well as the chiral order in the assemblies can be controlled by the addition of monofunctional OPV derivatives.