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Unlike the addition of a second equivalent of diazoalkane to C60, which does not show marked selectivity, the addition of azides to C60 shows chemo and regio selectivity [4]. Utilization of this unique selectivity, led us to the preparation of the first heterofullerene ‘C59N’ in bulk quantity [5, 6]. Herein we report on its synthesis and mechanism of formation. We also describe the application of this procedure for the formation of higher heterofullerene analogs, i.e. ‘C69N’ isomers [7] and introduce methodology that opens a viable route to the functionalization of azafullerenes [8]. The azafullerene (C59N)2 can be synthesized from C60 in three steps. The initial step in the formation of azafullerenes is the 1,3-dipolar cycloaddition of 2methoxyethoxymethyl azide (MEM-azide) [9]. Not unlike the addition of diazoalkane, the addition of an alkyl azide to C60 occurs across the [6,6] bond. At room temperature, the initially formed triazoline can be isolated in 35-40% yield. Thermolysis of the triazoline, followed by concomitant loss of nitrogen, gives rise to azafulleroids and fulleroaziridines. Fulleroaziridines and azafulleroids can also be obtained directly from C60 at higher reaction temperatures (160-180°C).

We present electron energy-loss spectroscopy studies in transmission of the electronic structure of (C59N)2. The overall broadening observed for the π-derived structures in the low energy-loss function of (C59N)2 when compared to C60 is due to the reduced symmetry of the heterofullerene. The optical gap of (C59N)2 is about 1.4 eV, slightly smaller than that of C60 (1.8 eV). Using a Kramers-Kronig analysis the dielectric function in the low energy region was calculated. A static dielectric function at zero energy of ∼ 5.6 is found.