3‘,4‘-Dibutyl-5,5‘‘-diphenyl-2,2‘:5‘,2‘‘-terthiophene (Bu2Ph2Tth) can be readily converted to the stable cation radical [Bu2Ph2Tth]+. The hexafluorophosphate salts of the cation radical ([Bu2Ph2Tth]PF6) are synthesized in millimolar quantities by either chemical or constant current electrochemical oxidation; the latter method gave X-ray quality single crystals. X-ray powder diffraction studies indicate the materials from both syntheses have the same structure. The crystal structure of [Bu2Ph2Tth]PF6 was determined and is temperature dependent. At 293 K, [Bu2Ph2Tth]PF6 crystallizes in the C2/c space group while at 106 K it belongs to the P21/n space group and exhibits a superlattice structure where the c axis is approximately double that at 293 K. Both structures consist of columnar “slipped π-stacks” of [Bu2Ph2Tth]+ cations and channels of PF6 - anions. At 293 K, the cations stack with a regular interplanar contact distance of 3.47 Å; at 106 K, the contact distances alternate regularly such that each cation has interplanar contact distances of 3.36(5) and 3.42(5) Å with the two neighboring cations in the π-stack. The crystal structure of Bu2Ph2Tth was also determined, and comparisons are made to the structure of [Bu2Ph2Tth]PF6. Several physical techniques (UV−vis−NIR−IR absorption, spectroelectrochemistry, ESR, conductivity) were used to investigate the electronic structure of the cation radical in solution, embedded in a thin film polymer network and as a pure solid sample. The measured physical properties correlate with the crystal structures of [Bu2Ph2Tth]PF6 and indicate that the material has a band-like electronic structure characteristic of a semiconductor.

Generations 1−5 of poly(amidoamine) (PAMAM) dendrimers were peripherally modified with cationically substituted naphthalene diimides. Reduction with sodium dithionite in water or formamide formed anion radicals on the diimide moieties. Evaporation of water under argon produced powders of the reduced dendrimers that were electrically conductive. Using formamide as solvent, films were cast of reduced generation-3 modified dendrimers. Fully reduced films (1.1 e/diimide) gave conductivities under ambient conditions of about 10-3 S/cm. Films formed from these dendrimers that were half-reduced (0.55 e/diimide) gave σ = 10-2 S/cm. Near-infrared (NIR) spectra on the films showed the formation of π-stacks with maximum absorbance beyond 2000 nm. The wavelength and intensity of this absorbance correlated with the conductivity. The conductivity increased with increased humidity above the films reaching values as high as 18 S/cm at 90% relative humidity. The conductivity was in all cases electronic and isotropic. The conductivity−humidity effect was probed by NIR spectroscopy, X-ray powder diffraction, and quartz crystal microbalance measurements. These studies suggest that the amorphous films absorb water from the air and at high humidity they are plasticized, allowing faster stack-to-stack electron hopping and increased conductivity.

We report the first example of a dendrimer that is electrically conducting. The conducting film was formed from a poly-(amidoamine) (PAMAM) dendrimer that had been modified on its periphery with naphthalene diimide anion radicals. These anion radicals, aggregated into a -stacked network, provide the pathway for conductivity.Because conducting polymers typically have conjugated main chains,1 and because dendrimers are a relatively new class of polymers,2 it is not surprising that this is the first example of a conducting dendrimer. On the other hand, we must comment on the paucity of examples of well-characterized conducting polymers formed from any polymer with redox groups attached to a nonconjugated main chain.3 The present investigation has its origins in previous studies that established that diimide anion radicals like 1" (made water soluble with the pyridinium groups) aggregate into -stacks in aqueous solution4 and form stable conducting polymer films when embedded in PVA or a cationic

Poly(amidoamine) (PAMAM) dendrimers, generations 1-6, were peripherally modified with cationically substituted naphthalene diimide groups. Several monomeric diimides were also prepared as models. The structure and loading of the dendrimers were determined by vis, IR, and NMR spectroscopies, elemental analysis, and coulometric analysis. In general it was possible to obtain loadings greater than 70% even from generation 6 dendrimer where there are 192 amine groups to be substituted. These polymers and monomers were reduced using sodium dithionite or electrochemically with one electron per imide group converting each imide into its anion radical. Near-infrared (NIR) spectroscopy showed that in D 2 O or formamide solutions the anion radicals aggregated into π-dimers and π-stacks. Cyclic voltammograms are interpreted in terms of anion radical aggregation and precipitation of the reduced dendrimers. The CV and NIR results for the various dendrimer generations were quite similar. These results allow insight into the possibilities and limitations of dendrimers to provide a scaffold for intramolecular aggregation.