Positive and Negative Charge Carriers in Doped or Photoexcited Polydithienothiophenes:  A Comparative Study Using Raman, Infrared, and Electron Spin Resonance Spectroscopy

Abstract

Poly(dithienothiophene)s (PDTTs), low band-gap conjugated polymers with polythiophene-like chain where an aromatic thienothiophene moiety is fused to each thiophene ring, were studied using Raman spectroscopy, photoinduced infrared absorption, as well as attenuated total reflection Fourier transform infrared (ATR-FTIR) and electron spin resonance (ESR) spectroelectrochemistry. The spectroelectrochemical studies were performed in situ during p-and n-doping (electrochemical oxidation and reduction, respectively). Raman lines of the pristine polymers are compared to infrared active vibration (IRAV) bands due to the charge carriers injected by the electrochemical doping processes or by illumination. The different π-electron distribution along the polythiophene-like chain, which determines the different band-gap sizes, also account for the different lattice relaxations and vibrational behaviors shown by these polymers. By means of in situ ESR spectroscopy, the formation of paramagnetic positive and negative charge carriers with unusually high g-factors could be proved.

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

“…[73][74][75][76] Moreover polarons carry unpaired spins, thus their formation and recombination to bipolarons can be monitored by EPR spectroscopy. [77][78][79][80] Spectroscopic parameters of the investigated polymers in the neutral and p-doped states are collected in Table 9. With the exception of poly (4), in the spectra of thin films of neutral polymers a clear vibrational structure can be seen, which is the most pronounced in poly(3).…”

Infrared signatures of positive and negative charge carriers in conjugated polymers with low band gaps

“…Aromatic systems fused to thiophene rings increase the quinoidal character of the thiophene units and the pelectron delocalisation along the polymer chain [30,31], resulting in band gap values of 1.15 eV for PDTT1, 1.12 eV for pDTT2 and 1.05 eV for PDTT3 [32]. Despite the structural similarities, the different position of the sulfur atom in the outermost fused ring influences the aromaticity of the thiophene ring incorporated in the chain and therefore the electronic and the vibrational behaviour [21].…”

“…5 the in situ spectra for p-doping and ndoping of PDTT1 are compared (data taken from [21]). The sharp band at 842 cm À1 , growing during the pdoping of all PDTTs, is due to the incorporation of hexafluorophosphate ions balancing the charge formed on the polymer by the oxidation process.…”

“…1. Details of the characterisation of the compounds and their general properties are described in previous publications [18][19][20][21].…”

Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

“…Indeed, polaronic absorption in polymers is very well established. 16,17,[19][20][21][22][23] However, very few studies thus far have explored spectroscopically both electron and hole polarons in the same system, made possible by the emergence of ambipolar DA polymers. In recent work on homopolymer polyseleneophene 24 using charge-modulation spectroscopy (CMS), Chen et al studied the origin of the different transport characteristics of electrons and holes in a semi-crystalline ambipolar polymer.…”