SPECTROSCOPIC CHARACTERIZATION OF PEDOT:PSS CONDUCTING POLYMER BY RESONANCE RAMAN AND SERRS SPECTROSCOPIES

Figure 1
(a) Typical experimental RR spectrum of PEDOT:PSS as synthesized with 12 hours, when using exciting radiation with wavelength at 1064 nm. Inset: bisEDOT representing the nomenclature based on the position of the carbon atoms relative to the sulfur atom. The dihedral angle represented by the two pairs of bonds marked with red and blue circles were set to 180 ºC to represent the most stable conformation of the EDOT_n oligomers; (b) variation of the bond order index, theoretically obtained for the C_αC_β bond along the subsequent EDOT units, for the EDOT₁₆ oligomer obtained from the B3LYP/6-31G(2d) level of theory calculations. Inset: structure of the EDOT₁₆ oligomer

Figure 2
(a) UV-VIS-NIR spectra of PEDOT:PSS as a function of reaction time; (b) RR spectra of PEDOT:PSS in the wavenumber range of double bond stretching, as a function of reaction time, and (c) in the same spectral interval after 12 hours of reaction. All spectra were obtained at 23.0 ºC and using exciting radiation with wavelength at 1064 nm

Figure 3
(a) Reaction time dependence of the maximum of the band observed at 1426 cm^-1 region in the experimental RR spectra of PEDOT:PSS; (b) theoretical wavenumbers obtained for the band at 1554 cm^-1 of EDOT₁₆ oligomer (ν_s(C_αC_β)oxidized) with charge density varying from 0 to +6 a.u.; (c) simulation data for the band at 1561 cm^-1 (ν_s(C_αC_β) reduced) as function of the number of the residues for a series of EDOT_n oligomers with n varying from 2 to 16 residues. Two different regions marked in (a) are correlated with (b) as red triangles and (c) as white triangles. All spectra were obtained at 23.0 ºC and using 1064 nm laser line. Theoretical data obtained with the DFT methodology in the B3LYP/6-31G(2d) level of theory

Figure 4
Time dependence of the RR spectra of PEDOT:PSS observed at 1350-1500 cm^-1 region when using exciting radiation with wavelength at (a) 785 nm and (b) 1064 nm; (c) intensity ratio of 1426 cm^-1 and 1443 cm^-1 bands, as function of reaction times, taken from the spectra obtained with 785 nm excitation and (d) maximum of the band at 1427 cm^-1 as function of the reaction time, taken from the spectra obtained with 1064 nm excitation. All syntheses were carried out with temperature fixed at 30.0 ºC

Figure 5
Time dependence of the SERRS spectral patterns of PEDOT:PSS, in comparison with its RR spectra, observed (a) from 1600 to 1200 cm^-1, and (b) from 900 to 1050 cm^-1; (c) UV-VIS-NIR spectra of (i) AuNPs aqueous suspension, (j) PEDOT:PSS diluted in water and (k) the mixture of AuNPs with PEDOT:PSS. All syntheses were obtained with temperature fixed at 30.0 ºC, and all RR and SERRS spectra were recorded by using λ₀ = 785 nm. The bands at 1443 and 990 cm^-1 were used as internal pattern to normalize each spectrum