Molecular n-dopants achieve doping in conjugated polymers either by reduction of the host material by direct electron transfer or by decomposition of a precursor to an intermediate that is capable of reducing the host. Two examples of molecular n-dopants are the dimethylbenzimidazolium salts (DMBI-X), which release unidentified reactive intermediates during a thermal deposition process, and the 1,3-dimethyl-2,3-dihydro-1H-benzimidazoles (DMBI-H) which react as hydride donors. In either case, the benzimidazolium cation/host radical anion pair, DMBI+/A��, is believed to be the reaction product that results in additional carriers. For DMBI-I dopants, strong n-doping has only been observed for vacuum deposited films, while for DMBI-H dopants, doping is necessarily accompanied by hydride or hydrogen atom transfer. Here we report on the synthesis, characterization, and doping mechanism of benzimidazoline-radical dimers ((DMBI)2) and their use to form the doped state DMBI+/A�� in conjugated polymers. The distinct properties of the (DMBI)2 dopants relative to the DMBI-H dopants is evident from the doping rates, polaron intensities, Fermi level shifts, and conductivities achieved using (2-Cyc-DMBI)2 and 2-Cyc-DMBI-H. Greater variability of the doping effect was found for the DMBI-H compound than for the (DMBI)2 compound, which is attributed to the distinct reactions by which the dopants function. The present work demonstrates the importance of mechanistic understanding for achieving effective doping, and will advance the field by providing clear methodology for the preparation and utilization of potent (DMBI)2 dopants.

Effective n-doping of conjugated polymers by dimers of benzimidazoline radicals

248th National Meeting (2014)

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