Aggregation-induced planarization

A self-consistent picture arises, in which the optical changes of the PPEs upon thin-film formation can be attributed to an aggregation-induced planarization of single polymer chains. While the aggregation process involves many chains that enforce their mutual pla-... 

It will be interesting to note whether similar optical behavior, i.e., the occurrence of an aggregate-induced band, can be detected in differently substituted PPEs and PAEs. The future will tell whether the bathochromic shift observed for dialkoxy-PPEs is likewise due to planarization or has a different origin, but a paper by Scherf shows that dialkoxy-PPEs Im display a moderate Cotton effect in poor solvents with a distinct negative maximum at 475 nm (g= 0.001). The similarity of dialkyl- and dialkoxy-substituted PPEs with respect to their CD spectra suggests, but does not prove, that a related mechanism of aggregate formation may be at work. 

Subsequent pyridine-assisted polymerization induced a solvophobic orthogonal interaction, based on phenyl-boron-phenyl jt-stacking, leading to dispersible nucleation. On aggregation, pyridine-coordinated boronate ester polymers are converted into planar structures via elimination of pyridine, because the trigonal planar state of the boronate ester is thermodynamically favoured over the pyridine-coordinated tetrahedral structure. As a result, spherical particles composed of lamellar nanostructures are produced, and their size depends on the minimization of interfacial free energy... 

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