4, 4 -dimethoxy-2-2 -bithiophene

As reported by Heinze et al. poly(4,4 -dimethoxy-2,2 -bithiophene) oxidizes at 0.20 V vs. Ag/AgCl, combines moderate bandgap (1.60 eV) and high stability in the conducting state [66]. Based on its transparency in the oxidized state, this polymer has been proposed for hole injection in OLEDs [67]. 

Dietrich et al. reported in 1991 [39] that electropolymerization from 3-methoxythiophene leads, as it does from the dimer 3,3 -dimethoxy-2,2 -bithiophene, to a polymer with a very short conjugation length. By contrast, electropolymerization from 4,4 -dimethoxy-2,2 -bithiophene dimer leads to a polymer with extraordinary optical properties thin films of this polymer change colour from deep blue in the undoped state (with maximum absorption at 610 nm) to pale grey-blue in the oxidized state (the energy gap of this polymer is one of the lowest measured for conducting polymers). 

Dietrich and Heinze electrochemically prepared poly(4,4 -dimethoxy-2,2 -bithiophene [56]. Since the 5 and 5 positions were reactive due to the adjacent methoxy groups and were available for polymerization, a high-quality polymer was obtained. The polymer was electrochemically stable over a wide range of applied potentials. The thin films of the polymer were deep blue in the neutral state and a light gray-blue in the doped state. The neutral form exhibited a broad absorption in the visible region with a maximum at 610 nm. The doped polymer showed no absorption peaks in the range 300-850 nm. 

Fig. 5 Quartz crystal microbalance measurements during potentiodynamic polymerization of 4,4 -dimethoxy-bithiophene in CH2CI2, 0.1 M TBAPFe,...

Conformational analysis was carried out on the molecules shown in Figure 42 <2002CPL(363)18>. One group consists of thiophene-phenylene-thiophene (TPT) 178, dimethyl-substituted TPT (DMTPT) 179, and dimethoxy-substituted TPT (DMOTPT) 180, and the other group is composed of dihexyl-substituted bithiophene (DHBT) 175 and dicyclohexyl-substituted bithiophene (DCBT) 181. 

Regioregularity of poly(3, 3 dimethoxy-2, 2 -bithiophene), 278 Regioregular poly(3-alkylthiophene), 287 Regioregular polymers, 284... 

The influence of side group distribution on the properties of substituted PBTs has been studied [506,507]. Poly(4,4 -dibutyl-2,2 -bithiophene) and poly(3,3 -dimethoxy-2,2 -bithiophene) correspond in their chain geometry to head-to-head and tail-to-tail coupled 3-substituted PTs. In cyclic voltammetry both polymers exhibit much narrower oxidation peaks as compared to the corresponding head-to-tail coupled PATs and poly(3-alkyloxythiophenes). Poly(dialkyloxy-2,2 -bithiophene)s seem to be more stereoregular compared to poly(3-alkyloxythiophene)s [506,507]. 

Polymers derived from a-terthiophenes bearing a variety of fused central ring systems have been prepared. Three groups simultaneously reported on the polymerization of the monomer XLI (R = H) [64-66] prepared by different routes. This monomer affords the 1 1 alternating copolymer of bithiophene (BT) and isothianaphthene (ITN) with an gap of 1.7 eV. This value is intermediate to those of the corresponding homopolymers of BT ( =2.1 eV) and ITN ( 1 eV) [67]. Derivatives in which the heteroatom in the central ring was O [64-66] or N-CH3 [64,66] were also prepared, as was the dimethoxy compound (XLI, R = OCH3) [66]. 

---