Radical cations and anions from some simple polythiophenes: an ESR investigation

Radical Ions from 3,3′′′,3′′′″‐Tris(butylsulfanyl)‐2,2′:5′,2″:5″,2′′′,5′′′,2′′′′:5′′′′,2′′′″‐sexithiophene: An Experimental and Theoretical Study of the p‐ and n‐Doped Oligomer

“…(close to that of the free electron g 2.0023) indicates little participation of the heterocyclic sulfur atoms in delocalising the unpaired electron, thus reflecting a spin density distribution involving primarily the carbon backbone and analogous to that found for the radical cations of the smaller oligomers and of thiophene itself. [11,33,34] Indeed, Figure in the SOMO of 1…”

“…[3,4,9,10] As a consequence of the lower oxidation potential with respect to that of thiophene, radical cations of longer oligothiophenes can be easily generated by TFA also in the absence of metal ions. [3,11] Radical anions and dianions of alkyl-end-capped bithiophenes are instead unstable, [9] unless the alkyl groups are replaced by trimethylsilyl moieties. [12] Negative ions are more easily accessible in the presence of cyano and [13] nitro groups [14] or in the case of longer end-capped oligothiophenes.…”

“…Although several studies have been dedicated to the former species, [2±5, 7, 11, 12, 17] only few investigations have been focused on the latter ones. [11,12] The electron exchange between a diamagnetic molecule and the related radical ions induces substantial line broadening (the so-called paramagnetic broadening) in its 1 H NMR spectrum and may lead to the disappearance of proton signals even at low percentages of radical species. [18] Nevertheless, it has been reported that addition of small amounts of TFA to CDCl 3 solutions of substituted benzenes leads to the formation of such a low percentage of radical cation (( 1 %) that 1 H NMR spectra can still be observed although the linewidth of the individual signals may be significantly altered, [19,20] the extent of the broadening being related to the hyperfine coupling (hfc) constant observed in the EPR spectrum for each individual hydrogen atom.…”

1,1,1,3,3,3-Hexafluoropropan-2-ol as a solvent for the generation of highly persistent radical cations

“…This radical cation had T+ % 1 h. The 5-methoxy derivative of 1,3-benzodioxole (3) even by oxidation by tolyl-TI"' gave the dimer (4) spectrum [aCH, (4 H) = 0.518, aoMe (6 H) = 0.137, aH3'93" (2 H) = 0.105, a H 6 ' p 6 " (2 H) = 0.076 mT; lit.,27 aCHz (4 H) = 0.546, aoMe (6 H) = 0.140, aH6,6' (4 H) = 0.033 mTJ, attesting to the well-known, high propensity for 1,2,4-trialkoxybenzenes to undergo dimerization. 28 The 2,2'-bithiophene radical cation (14a'+) is a reactive species, prone to undergo dimerization to quaterthienyl in trifluoroacetic acid.29 Its EPR spectrum was previously 30 recorded by low-temperature oxidation (irradiation in the presence of Hg" trifluoroacetate) of 2,2'-bithiophene in dichloromethane-trifluoroacetic acid. In HFP, tolyl-TI"' oxidation of 2,2'-bithiophene gave a weak spectrum of a radical cation [aHs9" (2 H) 0.77, a H 4 y 4 ' (2 H) 0.027, a H 3 y 3 ' (2 H) 0.385 mT; lit.,30aH5*5'(2H)0.327,aH4,4'(2 H)0.222, ~" ~, ~' ( 2 H)O.l06mT].…”

A DFT/TDDFT mission to probe push–pull vinyl coupled thiophene oligomers for optoelectronic applications

“…34 Among these polyheterocycles, thiophene oligomer is a subject of considerable interest due to its simple structure, and these oligomers have been used as models [35][36][37][38][39][40] to study the electronic properties of polythiophene. [41][42][43][44][45][46][47] Therefore, the use of thiophene based molecules is inevitable in the fabrication of materials for solar cells. 48 Recent developments in small molecule organic solar cells (SMOSC) mainly use these conjugated oligomers.…”