Poly mechanochromism

Recently, Lee, Kwak, and coworkers have reported on mechanochromic photoluminescent LC polymer 5 (Fig. 5) [32]. This poly(diphenylacetylene) derivative has flexible dimethyloctadecylsilyl side chains. A solvent cast film made from toluene solution of compound 5 shows a smectic LC phase above 5 °C and phase transition to the isotropic phase is not observed until 200 °C. The cast film of compound 5 shows a blue emission. An orange emission can be observed when mechanical stimulus is induced to the cast film of compound 5. In the emission spectra, an additional shoulder appears after the mechanical stimulus is induced. The longer wavelength component is attributed to forming intermolecular excimers. The sky blue emission is recovered by annealing of compound 5 in hexane. 

Although the property of interest in all of the above-mentioned cyano-OPV-containing materials was a mechanically induced change of the photoluminescence color (i.e., a mechanically induced transformation from an excimer-rich to a monomer-dominated emission), certain cyano-OPVs also display a changed of their absorption color upon (dis)assembly. Thus, Kunzelman et al. reported mechanochromic blend films based on C18-RG and either poly(ethylene... 

Lott J, Weder C. Luminescent mechanochromic sensors based on poly(vinylidene fluoride) and excimer-forming /7-phenylene vinylene dyes. Macromol Chem Phys 2010 21 l(l) 28-34. 

The original idea to exploit excimer-forming dyes as mechanochromic transducers in polymers (as opposed to neat low-molecular-weight compounds) was inspired by the work of Trabesinger et al. [50] who showed that aggregated poly(phenylene ethynylene) guest molecules in a polymeric matrix could be dispersed by simple deformation of the material. This deformation transformed the material from a... 

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