Poly(3-hexylthiophene-2,5-diyl) (P3HT) is widely used in organic photovoltaics because of its broad light absorption and relative good photostability. Raman spectroscopy has been used to study the morphology of the conjugate polymer thin in the presence of fullerene under various annealing and solvent conditions to reveal the structural changes of the polymer in a real device environment. This study uses nanotextured silver film as surface Plasmon source for single molecule Raman spectroscopy of single conjugate polymer. Our study indicates that P3HT shows extremely stable Raman spectra with long lifetime in comparison to the R6G single molecule trajectories. Four kinds of solvent including chlorobenzene, dichloromethane, toluene, and tetrahydrofuran are used to help understand the solvent dependence and Raman signature of the conjugate polymer on nanotextured silver substrates. Raman spectra of ensemble and single molecules are compared. More than twenty single molecules were probed per solvent with their results indicating good agreement with the ensemble measurements. Our study shows that toluene showed the most Raman bands in its spectra but similar overall intensity was seen in the trajectories using all solvents, indicating solvent plays a critical role in defining the folding of the molecule on the surface. Time dependent Raman spectra were measured with 30 seconds per spectrum using a spectrometer with a nitrogen-cooled CCD camera. The spectra showed increases and decreases in various Raman band intensities independent of the solvent. Polarization effects were confirmed by varying the incident light polarization and help indicate the single molecule capability. We also present the fluorescence background of the silver substrate such as silver nanowires and the dependence of Raman signal of small molecules on the aggregation states of single nanowires and the changes in the polarization angle of incident light to reveal the relationship between the field enhanced fluorescence of silver and Raman.

Single molecule surface enhanced Raman of poly (3-hexylthiophene-2, 5-diyl) and substrate dependence of surface enhanced Raman

243rd National Meeting (2012)

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