ESR Characterization of Oligomeric Thiophene Materials

Abstract

AD-A281 176 'The ESR of electrooxidation products of orthogonally bridged dimers of ,a-Coupled thiophene oligomera and spiro-fused phenylene-thiophene mixed oligomers was studied as a function of temperature. ESR measurements on the one-electron oxidation products indicate that the charge remains on a single oligomer unit and does not hop between the two bridged oligomer chains for temperatures up to 300 K. This is evident from the presence of hyperfine structure in ESR spectra for the dimers of short-chain oligomers and the small temperature-dependent line broadening for longer chain spiro dimers, characteristic of a low-energy process such as the paramagnetic site moving along the oligomer chain length. The activation energy for a paramagnetic center moving along the oligomer chain length has been estimated at <100 cm 1 . The incorporation of phenylene into the oligomer unit shifts oxidation potentials anodic and also inhibits the mobility of the polaron along the Ahconjugated oligomer segment. Evidence for formation of u-u dimers in solutions of 7-mT has also been obtained. The ESR of electro-oxidatlon products of orthogonally bridged dimers of aa-coupled thiophene oligomers and spiro-fused phenylene-thiophene mixed oligomers was studied as a function of temperature. ESR measurements on the one electron oxidation products indicate that the charge remains on a single oligomer unit and does not hop between the two bridged oligomer chains for temperatures up to 300K. This is evident from the presence of hyperfine structure in ESR spectra for the dimers of short chain oligomers and the small temperature dependent line broadening for longer chain spiro dimers, characteristic of a low energy process such as the paramagnetic site moving along the oligomer chain length. The activation energy tor a paramagnetic center moving along the oligomer chain length has been estimated at <100 cm-I. The incorporation of phenylene into the oligomer unit shifts oxidation potentials anodic and also inhibits the mobility of the polaron along the x-conjugated oligomer segment. Evidence for formation of x-x dimers in solutions of 7-mT has also been obtained.

Redox States of Long Oligothiophenes: Two Polarons on a Single Chain

“…In this respect it interesting to note that the dications of orthogonally bridged and spiro-fused phenylene ± thiophene mixed oligomers were also found to produce no or very weak ESR signals under conditions where UV/visible/near-IR data suggest the presence of a single charge in each of the two orthogonal oligomer units. [61] Therefore, based on all experimental results obtained from UV/visible/near-IR, ESR, and ESMS, we propose the most likely electronic configuration for the dication of 12T is that of a 1 A g singlet ground state carrying two individual polarons, although direct spectral evidence for this proposition could not be obtained.…”

Poly(3-decylthiophene) Radical Anions and Cations in Solution: Single and Multiple Polarons and Their Delocalization Lengths in Conjugated Polymers

“…The position of intragap states is influenced by structural deformation and reflected in the transition energies . From the plots of transition energies of T n cations against 1/n and comparisons with polythiophene cations, a delocalization length of positive polaron n ≈ 12 was deduced. ,− van Haare et al . oxidized T 6 , T 9 , T 12 and observed shift of absorption spectra from T 6 +• to T 9 +• to T 12 +• .…”

Linear Monodisperse π-Conjugated Oligomers: Model Compounds for Polymers and More

“…[238] Later, it was shown that the positively charged center (polaron) migration in 87 along the p-conjugated chain has an activation energy barrier of less than 100 cm À1 . [239] Among functionalized oligo(a-thiophene)s [240] and corresponding (S,S)-dioxides, [241] methylthio derivatives such as 89 (Scheme 29) are of particular interest, since they exhibit high phototoxic activities against nematodes, larvae and eggs of insects, bacteriae, algae, and fungi as a result of their ability to photosensitize the formation of singlet oxygen ( 1 O 2 ). [ Scheme 29.…”