Infrared and multi‐wavelength Raman spectroscopy of regio‐regular P3HT and its deutero derivatives

Abstract

The recently synthesized regio‐regular poly(3‐hexylthiophene‐2,5‐diyl) selectively deuterated on the main chain backbone and/or on the hexyl side chain have given the opportunity to record their infrared (IR) and Raman spectra, and to carry out a spectroscopic study supported by density functional theory calculations. The Effective Conjugation Coordinate associated with the collective C=C stretching mode, with Raman scattering and IR absorption near 1,450 cm−1, is used as a probe of the electronic structure and the molecular conformation of the chain backbone. With the help of the data collected from the deuterated species, the vibrational assignment for the structurally relevant 1,600–1,300 cm−1 region has been clarified. The excitation‐dependent wavenumbers and intensities of the C=C stretching Raman modes are discussed. Raman spectra excited in‐resonance or off‐resonance show the existence of a multimodal distribution of effective conjugation lengths that are ascribed to a phase hairy‐A with a practically flat backbone chain, a phase hairy‐B where the conformation of the backbone is slightly distorted, and an amorphous phase. IR spectra provide additional information on the Effective Conjugation Coordinate.

Understanding the evolution of the Raman spectra of molecularly p-doped poly(3-hexylthiophene-2,5-diyl): signatures of polarons and bipolarons

“…C α -C β related vibrational modes are collective modes, in which several adjacent thiophene rings vibrate either in-phase or out-of-phase, and are strongly Raman active. 35 These modes include: (1) the symmetric vibration [C α -C β ] sym at ~1450 cm -1 , and (2) the asymmetric vibration [C α -C β ] asym at ~1500 cm -1 . Dispersion of the Raman peaks was observed with the length of oligomers (corresponding to the effective conjugation length in polymers).…”

Optimization of Sb2S3 Nanocrystal Concentrations in P3HT: PCBM Layers to Improve the Performance of Polymer Solar Cells

“…In the 2700–3100 cm −1 spectral region, the methylene and methyl stretching vibration bands from the hexyl side chains of the thiophene rings were notable. The P 3 HT polymer exhibited vibration bands at 2954 and 3054 cm −1 corresponding to the stretching and asymmetric vibrations of =C-H and C=C [ 40 , 41 ]. The band at 1260 cm −1 corresponded to the dipole-derivative vector perpendicular to the ring plane, and the band near 1048 cm −1 was due to C-H in-plane bending [ 42 ].…”

“…The band at 1260 cm −1 corresponded to the dipole-derivative vector perpendicular to the ring plane, and the band near 1048 cm −1 was due to C-H in-plane bending [ 42 ]. The vibration mode at 1454 cm −1 was due to the deformation vibrations of the CH and CH 3 [ 41 ]. The vibration modes in the 1600–1800 cm −1 region, such as 1715 cm −1 , were due to photo-degradation products, including C=O groups [ 43 ].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIII

“…Ahokas et al described their study on high vibrational overtone excitation‐induced conformational isomerization of glycolic acid in solid argon matrix . Brambilla and co‐workers synthesized regio‐regular poly(3‐hexylthiophene‐2,5‐diyl) selectively deuterated on the main chain backbone and/or on the hexyl side chain giving the opportunity to record IR and Raman spectra and to carry out a spectroscopic study supported by density functional theory calculations . Elorrieta and co‐workers used Raman spectroscopy to follow the laser‐induced oxidation of UO 2 .…”

“…[215] Brambilla and co-workers synthesized regio-regular poly(3hexylthiophene-2,5-diyl) selectively deuterated on the main chain backbone and/or on the hexyl side chain giving the opportunity to record IR and Raman spectra and to carry out a spectroscopic study supported by density functional theory calculations. [216] Elorrieta and coworkers used Raman spectroscopy to follow the laserinduced oxidation of UO 2 . Their results are particularly appealing for remote analyses, like those required in the analysis of nuclear fuel and nuclear waste.…”