Polydispersity of the photoluminescence quantum yield in single conjugated polymer chains

The conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was studied by a single-molecule imaging technique. A comparison of statistical distributions of fluorescence intensity with molecular weight distributions revealed that the distribution of the photoluminescence quantum yield of the single polymer chains under study is significantly asymmetric, with a polydispersity ≳2. The result implies that there are molecules whose quantum yield is a few times higher than the ensemble quantum yield. This conclusion suggests a possibility of a great improvement of the photoluminescence quantum yield of MEH-PPV, which is known to be several times less than 1.