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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) × 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 °C 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 π−π 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.
Schenning et al. (Thu,) studied this question.