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 a 10(-2) S/cm. Near-infrared (NIR) spectra on the films showed the formation of pi-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.