A theoretical study on the reaction of diazocompounds with C₇₀ fullerene

Highlights: • Functionalization of a C₇₀ with diazocompounds was studied by DFT. • Stability [5,6]-fulleroids shows the same trend to that observed experimentally. • The reaction energy is in the range of −23.3 to −37.7 kcal/mol. • Orbital analysis explains the experimentally observed UV–vis spectrums. • Theoretical ¹H NMR results are in excellent agreement with the experimental. - Abstract: Using density functional theory calculations, we investigated the chemical functionalization of a C₇₀ fullerene with diazocompounds which has been reported experimentally. The results indicate that the [5,6]-bond of the apex of C₇₀ is more reactive than the equatorial bonds toward the cycloaddition of the diazocompounds. The energetic stability of phenyl C₇₁ butyric acid methyl ester (PCBM)-type [5,6]-fulleroids (products) shows the same trend (1 > 2 > 3 > 4) to that observed experimentally. The reaction energy for different isomers of [5,6]-fulleroids is in the range of −23.3 to −37.7 kcal/mol. Our frontier molecular orbital analysis explains the experimentally observed UV–vis spectrums and confirmed the formation of [5,6]-fulleroids rather than [6,6]-methanofullerenes. The electron–hole pair binding energy for C₇₀ is calculated to be about 0.6 to 0.9 eV. Theoretical ¹H-nuclear magnetic resonance (NMR), in good agreement with the corresponding experimental data, was used to more investigate the structure of the most stable complex.