Spin and charge interactions between nanographene host and ferrocene

Ferrocene (FeCp₂) was introduced as a non-magnetic guest molecule to activated carbon fibers (ACFs) as a nanographene-based host having localized spins originating from zigzag edges of graphene. The introduction of the guest molecule was confirmed by FTIR for ACFs-FeCp₂ introduced at 55 (150) °C (FeCp₂-ACFs-55(150)). The appearance of satellite Fe_2p peaks and the increase in shake-up peak intensity of the C_1s in the XPS spectrum proved the emergence of charge-transfer host-guest interaction in FeCp₂-ACFs-150, supported by the red-shift of the G-band in the Raman spectrum. The six-times enhancement in the spin concentration in FeCp₂-ACFs-150 compared with ACFs indicates the spin magnetism of the non-magnetic guest FeCp₂⁺ molecule induced by a charge-transfer host-guest interaction in the nanographene host. The larger ESR linewidth than that expected from the dipolar interaction estimated by the localized spin concentration suggests the exchange interaction between the nanographene and FeCp₂ spins. The narrowing of the ESR linewidth of FeCp₂-ACFs-55 upon higher excitation microwave power suggests the inhomogeneity of the environment for FeCp₂⁺ molecules in the nanographene host. The observed induction of spin magnetism by the interfacial interactions between the nanographene host and the guest molecules will be a promising strategy for developing a new class of molecular magnets.