Ultrafast dynamics of photoexcitations in conjugated polymers

Measurements are reported of the time-resolved photoluminescence (PL) from unoriented films of poly(p-phenylenevinylene) [PPV], poly[2-methoxy,5-(2'-ethyl-hexyloxy)-p-phenylenevinylene] [MEH-PPV] and a cyano-substituted derivative of PPV, CN-PPV. The PL features observed for PPV and MEH-PPV are consistent with the ultrafast formation and subsequent energy migration of intrachain excitons followed by their decay through radiative and non-radiative processes. The dynamics of the PL in CN-PPV is substantially altered compared to that of PPV and MEH-PPV films and also to that of CN-PPV in solution. A transient high energy feature is observed that is not seen in continuous-wave (CW) measurements and a long-lived low energy feature which corresponds to the CW PL. These results are consistent with the formation of inter-chain excitations in CN-PPV films.