Variable temperature single-molecule dynamics of MEH-PPV.

Herein, we continue our investigation of the single-molecule spectroscopy of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at cryogenic temperatures. First, the low temperature microsecond dynamics of single MEH-PPV conjugated polymer molecules are compared to the dynamics at room temperature revealing no detectible temperature dependence. The lack of temperature dependence is consistent with the previous assignment of the dynamics to a mechanism that involves intersystem crossing and triplet-triplet annihilation. Second, the fluorescence spectra of single MEH-PPV molecules at low temperature are studied as a function of excitation wavelength (i.e. 488, 543, and 568 nm). These results exhibit nearly identical fluorescence spectra for different excitation wavelengths. This strongly suggests that electronic energy transfer occurs efficiently to a small number of low-energy sites in the multichromophoric MEH-PPV chains.