A Density Functional Theory Study on the Hole Transfer in Fullerene Hydride C60H2

Abstract

As a novel and convenient method for modifying the hole-transport property of fullerene C60 materials, its hydrogenation, which gives C60H2, was considered. Firstly, for the analysis of the carrier-transfer mechanism between C60H2 molecules, the geometrical difference between C60H2 and C60H2+, the natural population analysis (NPA) charge, and the electron spin resonance (ESR) parameters of C60H2+ were calculated by density functional theory [B3LYP/6-311G(d)]. Secondly, the reorganization energies (λ) of eleven isomers of C60H2 with a small heat of formation ΔHf° were calculated and compared with that of C60. It was shown that the magnitude of λ of C60H2 isomers is closely related to the geometrical difference between C60H2 and C60H2+. On the basis of Marcus theory, a smaller λ results in larger hole mobility. It was found that six isomers of C60H2 have a smaller λ than C60 (169 meV). The smallest λ of C60H2 (102 meV), which is over 40% less than that of C60, belongs to isomer 2b. At 300 K, its hole-transfer rate constant (kht) is about 2.5 times as large as that of C60. It is remarkable that two synthesized isomers, 0a and 2a, also have 20% smaller λ than C60, and the kht of these isomers are about 1.5 times as large as that of C60. These results indicate that the hydrogenation of C60 is an effective method for modifying the hole-transport property, and some isomers of C60H2 have potential utility as hole-transport materials.