Effect of triphenylamine as electron-donor evenly spaced in 2, 4, 6 and 8 thiophene units of the main chain: synthesis and properties

Abstract

Several poly(thiophene) derivatives containing triphenylamine (TPA) as electron-donor were synthesized by chemical homopolymerization in CHCl 3 media using FeCl 3 as oxidizing agent. Monomers containing TPA bonded by imine groups to terminal thiophene, bithiophene, terthiophene units allows polymerization to be performed in conditions similar to thiophene. TPA units are regularly spaced in 2, 4, 6 and 8 thiophenyl units in the main chain. TPA electron-donor effect on the polymers chains, as compared to poly(thiophene) was studied. Polymers, labeled as poly(TPA-Th), poly(TPA-biTh) and poly(TPA-Terth) were characterized by 1 H-NMR, FT-IR and UV-visible spectroscopy, elemental analysis, thermal stability (TGA) intrinsic viscosity, differential scanning calorimetry (DSC) and electrochemically using cyclic voltammetry (CV). The characterizations are consistent with the proposed structures. The polymers exhibited different optical absorption.They exhibited low intrinsic viscosity, a different effective conjugation and high thermal stability. Moreover, the polymers displayed two redox processes with a redox potential lower than that of poly(thiophene). Highest Occupied Molecular Orbital (HOMO), Lowest Unoccupied Molecular Orbital (LUMO) and optical band gap (E g ) were measured and the obtained values were compared with those of poly(thiophene). The effect of the presence of TPA units in the thiophenyl chains on HOMO, LUMO, band gap, redox potential and on TGA is reported. To complete the series, HOMO/LUMO levels and band gap of a polymer containing TPA with 8 thiophenyl units in the chain were determined using theoretical calculations. The results proved that, with respect to poly(thiophene), it is possible to decrease HOMO and LUMO without changing the band gap, projecting itself as a potential polymer to be studied in organic photocells.

New Triphenylamine-Based Oligomeric Schiff Bases Containing Tetraphenylsilane Moieties in the Backbone

“…The optical properties of polySBs were studied through UV-vis absorption and photoluminescence measurements using diluted polymer solutions. As shown in Figure 5 a, all polySBs exhibited two well-defined UV-vis absorption bands at around 270 and 400 nm corresponding to π–π* and n–π* transitions of the conjugated system and both TPA and imine moieties, respectively [ 7 , 44 , 45 ]. PolySB2 exhibited the highest maxima absorption at 473 nm (λ onset, Table 2 ).…”

“…Thus, polySB2, with a p -substitution in their biphenyl moiety, shows a red-shifted maximum absorption band (403 nm) which would be attributed to the difference of dihedral angle between the phenyl and biphenyl moieties. Furthermore, a higher degree of effective conjugation lengths can enhance the degree the π-electronic delocalization in the biphenyl-imine-triphenylamine segments [ 7 , 44 , 46 ].…”

“…This decrease of the orbital overlapping could also explain the lower intensity of the band at about 400 nm in comparison with the aromatic band at about 270 nm of polySB3. Therefore, a greater degree of effective conjugation lengths enhanced the degree the π-electronic delocalization in the biphenyl-imine-triphenylamine segments [ 7 , 44 , 46 ]. Table 2 also shows the calculated molar absorption coefficient (ε) for the samples, by indicating the ability of each polySB to capture light at the wavelength of analysis.…”

“…Likewise, the incorporation of m -di-substitution design of monomer in polySB3 induced a lower band-gap value as well as polySB2 (2.75 to 2.71 eV). On the other hand, polySB1 shows the higher band-gap, which would be associated to the lower conjugation lengths in the main chain mainly due to TPS-core linked to TPA unit through imine group [ 44 , 48 ].…”

Electronic and structural properties of polymers based on phenylene vinylene and thiophene units. Control of the gap by gradual increases of thiophene moieties

“…30,31 Poly(FVTeTh) shows several absorptions; the transitions of lower energy (maximum at 337 nm) correspond to species with different chain lengths in the polymer. 30,31 Poly(FVTeTh) shows several absorptions; the transitions of lower energy (maximum at 337 nm) correspond to species with different chain lengths in the polymer.…”