Excited-State Properties of Radical Anions of C70 and Its Derivatives: Significant Differences from the Case of C60
2017
Lü, Chao | Fujitsuka, Mamoru | Sugimoto, Akira | Majima, Tetsuro
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 findings highlight the essential roles of C₇₀•–* and its derivatives in associated semiconducting materials and provide a new strategy to explore the ET behaviors of higher fullerenes in various organic molecular devices.
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