ABSTRACT
Extensive computational simulations and experiments have been used to investigate the structure, dynamics, and resulting photophysical properties of a number para-phenylene vinylene (PPV)-based polymers and oligomers. These studies have shown how the morphology and structure are controlled to a large extent by the nature of the solute–solvent interactions in the initial solution-phase preparation. A good solvent such as dichloromethane generates noncompact structures with more of a defect-extended chain-like morphology while a bad solvent such as toluene leads to compact organized and folded structures with rod-like morphologies. Secondary structural organization is induced by using the solution-phase structures to generate solvent-free single-molecule nanoparticles. These nanoparticles are very compact and rod shaped, consisting of near-cofacial ordering of the conjugated PPV chain backbones between folds located at tetrahedral defects (sp3 C–C bonds). The resulting photophysical properties exhibit a significant enhancement in the photoluminescence quantum yield, lifetime, and stability. In addition, the single-molecule nanoparticles have Gaussian-like emission spectra with discrete center frequencies that are correlated to a conjugation length, allowing the design of nanoparticles that luminesces at a particular frequency. We followed a similar approach and applied a comparable methodology in our recent work on polythiophenes in order to study the effect of polymer architecture on nanoscale assembly. Unlike linear chains of comparable size, we observed aggregation of the bottlebrush architecture of poly(norbornene)-g-poly(3-hexylthiophene) (PNB-g-P3HT) after the freeze-drying and dissolution processes. The behavior can be attributed to a significant enhancement in the number of π–π interactions between grafted P3HT side chains.
