Generations 1-5 of poly(amidoamine) (PAMAM) dendrimers were peripheral
ly modified with cationically substituted naphthalene diimides. Reduct
ion with sodium dithionite in water or formamide formed anion radicals
on the diimide moieties. Evaporation of water under argon produced po
wders of the reduced dendrimers that were electrically. conductive. Us
ing formamide as solvent, films were cast of reduced generation-3 modi
fied dendrimers. Fully reduced films (1.1 e/diimide) gave conductiviti
es under ambient conditions of about 10(-3) S/cm. Films formed from th
ese 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 i
ntensity of this absorbance correlated with the conductivity. The cond
uctivity increased with increased humidity above the films reaching va
lues as high as 18 S/cm at 90% relative humidity. The conductivity was
in all cases electronic and isotropic. The conductivity-humidity effe
ct was probed by NIR spectroscopy, X-ray powder diffraction, and quart
z crystal microbalance measurements. These studies suggest that the am
orphous films absorb water from the air and at high;humidity they are
plasticized, allowing faster stack-to-stack electron hopping and incre
ased conductivity.