Ultrafast depolarization of the fluorescence in a conjugated polymer

Abstract

The effect of the extent of $\ensuremath{\pi}$ electron conjugation on the primary photophysics in semiconducting polymers is reported. A rapid depolarization of photoluminescence and transient absorption, which indicates a reorientation of the transition dipole moment by $\ensuremath{\sim}30\ifmmode^\circ\else\textdegree\fi{}$ on a sub-100 fs time scale, is observed in the fully conjugated polymer poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV). In contrast, partially conjugated polymers exhibit a much slower depolarization. The results reveal rapid changes of exciton delocalization in the fully conjugated MEH-PPV driven by structural relaxation.