Single short-chain conjugated polymer studied with optical spectroscopy: A donor-accepter system

Single rodlike poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV), in which the chain length supports only two or three chromophores, was studied using optical spectroscopy in order to elucidate exciton dynamics within a single conjugated polymer. Emission at one to three discrete intensity levels coupled with on/off blinking was seen in the fluorescence time traces. Drops in emission intensity were accompanied in the majority of cases by an abrupt spectral blueshift and a corresponding increase in the fluorescence lifetime. Photon correlation measurements indicated that at any point in time there was only one emitter active. This suggests that the two or three chromophores in a short-chain polymer act as a typical donor-acceptor system with energy absorbed by the donors (shorter chromophores) transferring to the acceptor (longer chromophore) along the polymer backbone before emission. Once the acceptor is quenched, a donor takes turns to emit.