Temperature effect on single chain MEH-PPV spectra

We report single molecule photoluminescence spectra of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in PMMA-matrix at 293 and 20 K with 90 s acquisition time. All spectra at 293 K are very similar, contrary to literature results with acquisition times <5 s. We propose that fluctuations of conformations with distinct emission properties cause broadening of the spectra and reduce the differences in fluorescence spectra between separate chains. At 20 K the spectrum from a single chain consists of a few narrow peaks with absence of major spectral evolution within tens-of-minutes. The emission from distinct chains is spread over 3000 cm−1 characterizing different frozen conformations.