This paper describes a series of three-ring phenylene-ethynylenes (PEs) in which specific, non-covalent arene-arene interactions control conformation in the solid-state. As determined by single crystal X-ray structures, edge-face interactions between benzyl ester side chains and conjugated main chains are observed. In contrast, perfluorobenzyl ester side chains interact cofacially with main chains... read more, resulting in ∼60° torsional angles between neighboring aryl rings in crystalline PEs. Absorbance and fluorescence spectra of films of these compounds reflect these conformational effects, with the spectra of perfluorobenzyl-substituted compounds shifting hypsochromically from solution- to solid-state. In a demonstration of how balancing non-covalent interactions can open the way to new responsive materials, a main chain twisted derivative with octyloxy substituents displayed significant piezochromic behavior.read less
Pawle, R. H.; Haas, T. E.; Müller, P.; Thomas, S. W., III "Twisting and Piezochromism of Phenylene-Ethynylenes With Aromatic Interactions Between Side Chains and Main Chains" Chem. Sci., 2014, 5, 4184-4188. doi: 10.1039/c4sc01466a.