No abstract

No abstract

No abstract

It is demonstrated that Lewis acid doping of polyaniline in the oxidation state of emeraldine can be conveniently monitored by 57 Fe Mo ¨ssbauer spectroscopy if FeCl 3 is used as the dopant. The spectrum of doped polyaniline consists of two doublets with distinctly different Mo ¨ssbauer parameters which can be unequivocally ascribed to two types of complexing sites (amine and imine nitrogens). From the temperature dependence of the isomer shift and the recoil free absorption, we have calculated Mo ¨ssbauer lattice temperature Θ m ′ as probed by both complexing sites, which were 83 K for the amine and 126 K for the imine sites. These low values of Θ m ′ imply significant mobility of the dopant at temperatures close to room temperature, which is typical of small molecules inserted into polymer matrices. FeCl 3doped polyaniline is soluble in nitromethane, and acetonitrile and films cast from these solvents show conductivity of 0.2 S/cm. FeCl 3 -doped polyaniline is also a strong near-infrared absorber.

In situ electron spin resonance (ESR) and UV-vis spectro-electrochemical studies have been performed on two copolymers consisting of alternating subunits of regioregular head to tail (HT) coupled 3-octylthiophene tetramer and 2,2'-bipyridine subunits (P4) or 3-octylthiophene hexamer subunits of the same regioregularity and 2,2'-bipyridine subunits (P6). Both P4 and P6 have been investigated in their metal-free form as well as in the ruthenium(II) metalated form (P4-Ru and P6-Ru). P4 and P6 in the p-doped state exhibit a clear ESR signal characteristic of the presence of polarons in the oligothienylene subunits. In the case of P4, no recombination of polarons into bipolarons is observed, whereas the recombination process takes place in P6. The formation of bipolarons is well-rationalized in terms of the conjugation length, and it seems clear that the higher length of the oligothiophene subunit in P6( )()stabilizes bipolarons(.)() The same effect, is induced by the coordination of -Ru(bpy)(2)(2+) to the bipyridine unit in the metalated form of both polymers, which results in an increase of the conjugation length. Important information is gained from the analysis of the ESR spectra of both nonmetalated and metalated in the oxidized (p-doped) and reduced (n-doped) forms. In the p-doped state both nonmetalated and metalated polymers reveal the presence of a narrow ESR line characteristic of the mobile spin carriers in the polymer matrix. The oxidation of the metal center occurs at higher potentials and leads to an irreversible destruction of the system. To the contrary, in the reduced (n-doped) state the ESR lines of the nonmetalated and metalated polymers markedly differ. A significant line broadening with simultaneous change of the g-value is caused by spin-orbit coupling phenomenon induced by the presence of the coordinating metal. Finally, the observation of a clear polaronic band in the UV-vis spectrum of p-doped P4 and its strong dependence on the applied potential can be clearly correlated with the potential induced changes in the ESR spin density. The same applies to P4-Ru, where the changes in the polaronic and bipolaronic bands can also be correlated with the ESR spin density changes.

No abstract

No abstract

No abstract