Excited-State Properties of Radical Anions of C70 and Its Derivatives: Significant Differences from the Case of C60

Abstract

Excited-state dynamics of the C70 radical anion (C70•–*) were investigated for the first time by applying femtosecond laser flash photolysis to reduced C70 and its derivatives, including C70•–, C70H•–, C70•–-pyromellitimide (PI), and C70•–-naphthalenediimide (NDI)•–. The transient absorption spectra of C70•– and C70H•– upon near-infrared laser excitation revealed the relaxation processes of the D1 and vibrational hot ground (D0hot) states. Chemical modification of C70 was found to decrease the excited-state lifetimes. In the cases of dyad molecules (C70•–*-PI and C70•–*-NDI•–), the deactivation occurring through dual intramolecular electron transfer (ET) pathways from both C70•– (D1) and C70•– (D0hot) was revealed by spectroscopic analysis. Furthermore, the ET pathways for C70•–*-NDI•– generating NDI2– were proposed based on the energetically preferred products. The differences observed between the dyad systems of C70•–* and C60•–* can be explained by the lower geometric symmetry of C70. The current findi...