Fullerene Thin Films Functionalized by 1,5-Diaminonaphthalene: Preparation and Properties

The gas-phase treatment with 1,5-diaminonaphthalene (DAN) is proposed as an efficient way of chemical functionalization of fullerene C-60 thin films in order to modify their electronic properties; a temperature of 190 degrees C and reaction time of 4 h were found to be optimal reaction conditions. Two amino groups of DAN add on two neighboring C-60 cages, thus producing cross-links in the fullerene phase. The resulting oligomeric and/or polymeric products exhibit a lower solubility in toluene as compared to pristine C-60 films. The functionalized films exhibit lower surface roughness, as found by atomic force microscopy. Raman spectra keep, with some decrease in intensity, the most important features of C-60 upon functionalization. The infrared band intensities corresponding to pristine fullerene decrease even stronger, where a number of new absorption bands appear not only due to DAN moieties, but also due to the covalently derivatized C-60 cages. The diamine molecules are able to penetrate throughout the entire fullerene phase to provide an efficient and uniform functionalization. As a result, the DAN-functionalized films exhibit higher conductivity as compared to that of pristine films not only along the surface layer, but also through the entire phase of C-60, by one and four orders of magnitude, respectively.