Radical Ions of α,α‘-Bis(diphenylamino)-capped Oligothiophenes:  A Combined Spectroelectrochemical and Theoretical Study

Abstract

A new homologous series of alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, prepared by a palladium-catalyzed coupling reaction of stannylated 2-diphenylaminothiophenes with 2-mono- or 2,5-dibromothiophenes and their homologues, was studied by in situ ESR/UV-vis/NIR spectroelectrochemistry. In general, the oxidation potentials of these oligothiophenes were found to be proportional to the inverse number of thiophene units. However, the potential slope of the first oxidation is completely different from that of higher oxidation steps. Trication radicals were identified by electron spin resonance (ESR) for higher thiophene homologues in addition to monocation radicals (polarons). According to the ESR hyperfine structures, the unpaired electron is delocalized in the conjugated system. In contrast to the parent alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, the UV-vis/NIR absorption maxima of the oxidized species strongly depend on the number of thiophene units. Spin-restricted and spin-unrestricted Kohn-Sham density functional calculations were used to explain and to understand these properties. Absorption wavelength and intensities were calculated by the time-dependent density functional response theory. Unrestricted density functional calculations of oligothiophene dications (bipolarons) with five or more thiophene rings result in spin-broken structures which may be considered as two-polaron biradicals (polaron pairs).

Quantitative in-situ EPR spectroelectrochemical studies of doping processes in poly(3,4-alkylenedioxythiophene)s

“…Its values, spanning from 2.0029 to 2.0037, can be explained in terms of spin-orbit coupling with fully occupied oxygen orbitals of the 3,4-ethylenedioxy group. Such values have been reported for PEDOT [17] and other oligo and polythiophenes [47][48][49] and the effect of g-factor increase with increasing oxidation level of long end-capped oligothiophenes has been reported in the literature [50]. g-Factors of Lorentz line are peculiarly low and appear to be less doping level sensitive than their Gauss line counterparts.…”

Functional Oligothiophenes: Molecular Design for Multidimensional Nanoarchitectures and Their Applications

“…175 The same group recently reported successful synthesis of diphenylamino-capped oligothiophenes 2.92 (n ) 5, 6, 7) up to a nonamer by the same route. 176,177 Alternatively, bi-and quaterthiophenes 2.92 Scheme 2.15 (n ) 0, 2) were prepared by oxidative dimerization of 2-diphenylamino-substituted thiophene and bithiophene with TiCl 4 . These oligomers were easily electrochemically oxidized, giving stable radical cations, which were studied by electron spin resonance (ESR) and spectroelectrochemical measurements.…”

Charge Delocalization in a Homologous Series of α,α′-Bis(dianisylamino)-Substituted Thiophene Monocations

“…15 Indeed, the oneelectron oxidized or one-electron reduced forms of several oligo-p-phenylene and oligo-p-phenylene vinylene systems could be described well as organic mixed-valence compounds in various experimental studies, [16][17][18][19][20][21][22][23][24][25] but until now there has been comparatively little conceptually analogous work on thiophene systems. [26][27][28][29][30][31][32][33][34][35] A notable exception is the recent study of the oxidized forms of bis (4-(alkoxyphenyl)amino) derivatives of dithienylethene and bithiophene and the finding that a mixed-3 valence description of these cations is meaningful. 36 Another exception is our own recent investigation of photoswitchable organic mixed-valence in dithienylethene systems.…”