Large spectral diffusion of conjugated polymer single molecule fluorescence at low temperature

The conductive polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4- phenylene vinylene) (MEH-PPV) was investigated by means of single molecule spectroscopy at 15 K. MEH-PPV single chains were deposited onto a surface from a toluene solution and covered with a polymer cap layer spin-coated from an aqueous solution for protection from air. The MEH-PPV molecules exhibited large fluorescence spectral diffusion with the range reaching 1000 cm−1. We concluded that conformational changes, affecting dispersive interactions and conjugation length, is the most probable mechanism of the observed effect. It is the matrix-free environment that allows the MEH-PPV chains to undergo sufficiently large conformational changes even at low temperature.