Description and importance of interchain excited states in conjugated polymer photophysics

We compare the photoluminescence (PL) of poly-p-phenylenevinylene (PPV) to that of one of its soluble derivatives, poly (2-methoxy, 5-(2(1)-ethylhexox y)-p-phenylenevinylene) (MEH-PPV). We show that excimers due to pi -orbital overlap of adjacent polymer backbones are formed in MEH-PPV in high quantu m yield. They do not emit light at room temperature, potentially explaining the reduction of PL yield ill MEH-PPV films relative to solution. The herr ingbone packing of polymer chains in PPV prevents pi-pi stacking, but low P L yields are observed anyway. We conclude that polymer design to inhibit in terchain registration is a questionable strategy to increase luminescence y ields. The low PL yield in PPV is ascribed to bound polaron pair formation and preliminary data suggest that these may also form upon photoexcitation of MEH-PPV films.