Supramolecular Materials from Triblock Rodcoil Molecules Containing Phenylene Vinylene

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Abstract

We report here on the synthesis and characterization of several triblock rodcoil molecules containing conformationally rigid and flexible sequences and luminescent chromophores based on phenylene vinylene. The molecules consist of blocks of oligostyrene, oligoisoprene, and a rigid rod block. The synthesis of the rod blocks required the preparation of new phenylene vinylene oligomers. On the basis of electron microscopy and X-ray diffraction experiments, these systems were found to self-organize into supramolecular nanostructures which in turn assemble into monolayers. The nanostructures have diameters between 3.5 and 5 nm, and the regularity of the nanostructures depends on rod-to-coil volume fraction. The layer spacing of one system is 6.0 nm when cast from solution but increases to 7.8 nm upon annealing at 150 °C, possibly as a result of an increase in aggregation number. Interestingly, the formation of supramolecular nanostructures and the observed hierarchical order in the materials formed by rodcoil molecules can be completely suppressed by lowering the rod-to-coil volume ratio. When the chemical structure of rod segments is changed, the nanostructures formed can undergo a drastic increase in aspect ratio. These changes in shape maybe linked to different tendencies for aggregation among rod segments. Absorption and emission spectra of supramolecular solids are similar to dilute solution spectra and different from those of similar disordered materials.

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