Dithiophene, 7//-cyclopenta

A copper-mediated cyclization of metallated thiophenes has been utilized to prepare polycyclic thiophenes and thiophene cyclophanes. Treatment of dibromide 106 in succession with M-butyllithium (halogen-metal exchange), zinc chloride (transmetallation), and copper chloride gave 7//-cyclopcnta[ 1,2-fc 4,3-6 dithiophene (107) <00H(52)761>. This conversion has also been achieved using a palladium-mediated cyclization performed in the presence of hexamethylditin . Copper-mediated cyclizations have also been applied to the syntheses of cyclopenta[2,l-6 3,4-A ]dithiophen-4-one (108) (three steps from 73) <00S1253> and cyclophane 109 <00CC2329>. 

The related polythiophene 64 has been produced in 63% yield by a Stille coupling from 2-(tributylstannyl)-3,4-(ethylenedioxy)thiophene and 2,6-dibromo-4f/-cyclopenta[2,l- 3,4- ]dithiophen-4-one catalyzed by PdCl2(PPh3)2 or Pd(PPh3)4 in refluxing toluene <2004CM3667>. 

The polymers of 4H-cyclopenta[2,l-b 3,4-//Jdi thiophene derivatives showed absorptions in the range 560-590 nm [03MM2705]. Some monomers are based on the nonaromatic (12 n electrons) 4H-cyclopenta[2,l-fr 3,4-l/]dithiophen-4-yl cation 580a (X = CH+) model which was expected to display a reduced HOMO-LUMO separation, compared to related aromatic fused systems (i.e., 580, X = S, O, NF1) (91JCS(CC)752). Polymers of 580 (X = S) showed absorption at 480 nm. Poly(dithieno[3,4-b 3, 4 -4J thiophene) showed an absorption at 590-610 nm (89SM(28)C507 97MI23). 

Cyclopenta[l,2-6 3,4-6 ]dithiophenes were formed by the internal attack of dithienyl carbenes <84ACS(B)533, 84JCS(P1)571>. 

The halogen-metal exchange reaction has been used almost exclusively for the formation of dithienylmethanes lithiated at thiophene /(-positions these derivatives give acceptable yields of aldehydes77 on reaction with dimethylformamide and of acids on carbonation.66 Particular use has been made of bis-J -lithiated compounds for the preparation (via oxidative coupling) of thiophene analogs of fluorenes.3,67 The synthesis of cyclopenta-[ 1,2-b 4,3-b]dithiophene (67) is typical (Eq. 23). 

Chonan, T. Takahashi, K. The synthesis of difluoro and dimethyl derivatives of 2,6-bis (dicyanomethylene)-2,2-dihydro-4/7-cyclopenta[2,1-6 3,4-6 ]-dithiophen-4-one (CPDT-TCNQ) and the conducting properties of the metallic salts based on the dimethyl derivative. Bull. Chem. Soc. Jpn. 2004, 77, 1487-1497. 

Brisset, H., Thobie-Gautier, C., Gorgues, A., Jubault, M., RoncaU, J., 1994. Novel narrow bandgap polymers from sp carbon-bridged bithienyls poly(4,4-ethylenedioxy-4H-cyclopenta[2,l-b 3,4-b[prime or minute] ] dithiophene). J. Chem. Soc., Chem. Commun., 1305-1306. 

Alkyl was introduced into insoluble PTh as side chain, producing the soluble and most successful P3HT polymer (Li et al., 2005). However, this alkyl side chain also decreases the crystallinity of polymer in the heterojunction blend, which is negative for high carrier mobility. It has been reported that with lower side chain density, the performance can be greatly improved. The latest report shows that the performance and stability can be both enhanced by reducing the side chain density on fluorinated poly(4-(2 -ethylhexyl)-4-octyl-4H-cyclopenta[2, l-h 3,4-h ]-dithiophene-2,6-diyl-a/f-6,7-difluoro-2,3-bis... 

Cyclopentadithiophenes. 3,4 -Dibromo-2,3 -dithienylmethane treated at -70° with n-butyllithium in abs. ether, the resulting soln. of the dilithio compound cooled and added dropwise under dry Ng during 0.5 hr. to a vigorously stirred ice-cooled suspension of anhydrous CuClg in abs. ether, stirring continued 6hrs. at 0° 7H-cyclopenta[l,2-b 3,4-c ]dithiophene. Y 46%. F. e. s. A. Kraak et al., Tetrahedron 24, 3381 (1968). 

Figure 28.3. Structural formulas of several electron-conducting polymers (a) frans-poly(acetylene), (b) cw-poly(acetylene), (c) poly(p-phenylene), (d) polyanUine (PAni), (e) poly(n-methylaniline) (PNMA), (f) polypyrrole (PPy), (g) polythiophene (PTh), (i) poly(3,4-ethylenedioxythiophene) (PEDOT), (j) poly(3-(4-fluorophenyl)thiophene) (PFPT), (k) poly(cyclopenta[2,l-b 3,4-dithiophen-4-one]) (PcDT), and (m) Mg polyporphine.

Like ordered CPs, random copolymers have also been prepared to cater optoelectronic and other applications [252,255-258,450,451 ]. For example, by coupling of mixtures of 5,5 -[2,2 ]bithiophene and cyclopenta[2,l-fo 3,4- ]-dithiophene (electron-donating units) and 2,1,3-benzothiadiazole... 

For example, the effectiveness of low-bandgap polymers in absorbing more light has been demonstrated by comparing P3HT CdSe- and PCPDTBT CdSe-based devices [187]. It can be seen from Figure 3.26a that low-bandgap CP poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,l-b 3,4-b0] -dithiophene)-alt-4,7-(2,l, 3-benzothiadiazole)] (PCPDTBT)... 

A couple of studies of copolymers of bridged bithiophenes and EDOT have also been reported, starting with the random copolymer 87 reported by Huang and Pickup [132] in 1998 (Chart 12.12). Copolymer 87 was prepared by electropolymerization of 4 1 mixtures of 4-dicyanomethylene-4ff-cyclopenta[2,l-b 3,4-b j dithiophene and EDOT to give films with conductivities of 0.052—0.69 S cm ... 

Ferraris, J.P. and XL. LamberL 1991. Narrow bandgap polymers Poly-4-dicyanomethylene-4H-cyclopenta[2,l-lr,3,4-l)]dithiophene (PGDM). / Chem Soc Chem Commun 1268. 

Huang, H. and P.G. Pickup. 1999. Oxygen-modified poly(4-dicyanomethylene-4H-cyclopenta[2,l-fi 3,4- b ] dithiophene) A tunable low band gap polymer. Chem Mater 11 1541. 

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