Interchain photoluminescence in poly(phenylene vinylene) derivatives

We calculate that in cyano-substituted poly(phenylene vinylene), CN-PPV, and poly[2-methoxy, 5-(2'-ethyl-hexyloxy)phenylene vinylene], MEH-PPV, the lowest-energy arrangement has the chains parallel, with the perpendicular distance between chains 3.4 Angstrom in the former case, 4.1 Angstrom in the latter. Although there is evidence that most of the excitations created by above-band-gap light are polaron pairs or excimers in both cases, only those in CN-PPV luminesce because the smaller interchain distance results in a much larger matrix element for emission.