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 C60 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 C60 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 C60 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 C60 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 C60 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 C60, by one and four orders of magnitude, respectively.