Enhanced single molecule fluorescence of conjugated polymer poly(3-hexylthiophene) on silver-nanocubes

We investigate the enhancement of poly(3-hexylthiophene) (P3HT) single molecule fluorescence using silver-nanocube as substrates. Results show that the silver nanocube substrate enhances the single molecule fluorescence of P3HT by about 7 folds and effectively improves the photophysical stabilities of individual P3HT molecules by delaying the photobleaching process. We find that the increase of the radiative decay rates, resulted from the coupling between photogenerated excitons and surface plasmon, is directly related to the observed fluorescence enhancement of P3HT. The enhanced local field provided by the silver-nanocube substrate also contributes to fluorescence enhancement via coupling. This coupling depends on the overlap between the emission frequency of the fluorophore and the surface plasmon field provided by the substrate. As the emission wavelength of the fluorophore gets closer to the surface plasmon resonance of silver nanocubes, the coupling becomes stronger, leading to greater fluorescence enhancement.