Thienothiophenes fused

A new fused thienothiophene, 2,3 5,6-bis(ethylenedithio)thieno[3,2- >]thiophene (112), was used to prepare conducting organic salts (95BCJ1193). 

Much like PITN and its analogs, various fused thienothiophenes have also found interest as potential precursors for low handgap systems (Chart 12.9). One of the early systems of promise were polymers of dithieno[3,4- 3, 4 -d thiophene (69), initially reported in 1988 hy Tahani and coworkers [91-93] to have an g of 1.1 eV (for a relevant discussion of prior work see Ref. [1]). Since 1995, however, a numher of new reports on poly(dithieno[3,4-( 3, 4 -d]thiophene) (69) have appeared. 

Stille coupling has been used by Li et al to synthesize the donor-acceptor co-polymer P23 consisting of dithienyl-DPP and fused thienothiophene (TT) units. OFET devices fabricated from this polymer showed a high hole mobility of 0.94 cm V s due to significant intermolecular %-% donor-acceptor interactions between TT and DPP fused heterocyclic units.Additionally, a stannyl derivative of dithienothiophene has been recently co-polymerized by Shahid et al. with bis(5-bromo-2-thiophenyl)- and bis(5-bromo-2-selenophe-nyl)-DPP comonomers. Both polymers exhibited ambipolar characteristics in OFET devices. The thiophene-based co-polymer analog showed a higher... 

Several useful specialized reviews have appeared during the reporting period of this chapter. The chemistry of thienothiophenes <06AHC(90)125> and thienopyrimidines <06AHC(92)83> has been discussed in detail, whereas accounts of related interest highlight the field of thiaheterohelicenes <06OBC2518> as well as similar fused thiophene systems <06AG(E)8092>. 

Both thienothiophenes (3) and (7) were subjected to competitive electrophilic substitution reactions with thiophene. The fused heterocycles were always more reactive than thiophene in acetylation, Vilsmeier formylation and chlorination with NCS. While acetylation of both (3) and (7) occurrred at a comparable rate, formylation and chlorination occurred faster in the [3,2-6]-fused isomer (3) than in the [2,3-6] isomer (7). 

The UV spectral data of known parent A,B-diheteropentalenes are summarized in Table 9. The analogous thienothiophenes and selenolothiophenes show more absorption maxima in their UV spectra than the other systems. The known progressive shift of absorption to longer wavelengths which is observed in the simple five-membered heterocycles in the sequence furan < pyrrole < thiophene < selenophene is missing since the rings are fused. 

To construct additional heterocycles fused to the thienothiophene system, a number of approaches other than the above-mentioned photocyclizations were used. For example, heating 2-acetylamino-3-hydroxythieno[3,2-Z>]thiophene (206) in the presence of P2S5 afforded 2-methylthieno[3,2-fe]thieno[3,2-[Pg.158]

Tetrathiabenzo[l,3-cfirst time by dimerization of thieno[2,3- >]thiophene (142) (92PS73). More recently, it was found that catalytic reduction of 3,4-dibromothieno[2,3-i]thiophene (227) with an excess of activated zinc in the presence of bis(triphenyl-phosphine)nickel(II) chloride and tetraethylammonium iodide afforded only 4,4 -dibromo-3,3-bis(thieno[2,3- )]thiophene) (228) (in a maximum yield of 28%) (89AG1254). However, the reaction in the presence of a larger amount of the nickel catalyst afforded also dipenatlene 225. Optimization of the reaction conditions made it possible to increase the yield of the latter to only 14%. An alternative procedure was employed to transform thienothiophene 227 into trimethylstannyl derivative 229. The reaction of thienothiophene 227 with organotin intermediate 229 in the presence of the palladium triphenylphosphine complex afforded dipentalene 225 (13% yield). Derivatives 226 were prepared by lithiation of... 

The 7i-electron structure of thiophene, isomeric thienothiophenes and other fused sulfur-containing compounds (58 compounds, including those annulated with the... 

Isomeric thienothiophenes and their derivatives are of considerable interest as electron donors or acceptors for the design of new types of charge-transfer complexes and as ligands coordinating metal ions. As mentioned above (see Section IV.D), charge-transfer complexes of some five-membered fused heteroaromatic systems with TCNE were studied by UV and IR spectroscopy and their relative stabilities were discussed using the association constants and enthalpies of formation (82CS214). 

Poly(thienothiophenes), low band-gap conjugated polymers with a polythiophenelike chain where an aromatic thienothiophene moiety is fused to each thiophene ring, were studied using Raman spectroscopy and photoinduced IR adsorbtion (2002JPC(B)3583). 

Extending the structure of thienothiophene by an additional fused ring affords the family of dithienothiophenes, of which are there are six isomers (Chart 3.3). An excellent review on the synthesis and chemistry of dithienothiophenes was presented by Ozturk et al. in 2005 [45] and therefore the many different synthetic routes towards these materials will not be reproduced here. In their papers, Mastragostino and Sariciftci have termed four of the isomers DTT0-DTT3 for ease of reference (see Chart 3.3). 

The highest mobilities achieved in solution-deposited polymer transistor devices have been exhibited by thiophene-containing polymers. Thiophene is an electron-rich, planar aromatic heterocycle, which can form a range of conjugated polymers when coupled appropriately [23, 24], The crystalline nature of many thiophene derivatives plays a role in their excellent charge transport properties. In this chapter, we will focus on copolymers of thiophene with the fused unit, thienothiophene, and their structural analogues. 

In Chapter 3, Peter Skabara reviews the emerging subclass of thiophene-based materials, fused oligoth-iophenes. Special attention to this subclass of oligothiophenes is well justified by, among other reasons, the very high stability of a thienothiophene building block, which makes it popular for applications in thin-film transistors and photovoltaics. 

---