$\pi - $d Electron Coupling in Excited State in Organic-Magnetic Nanocomposites

The coupling between $\pi $ electron in organic semiconducting materials and d electron in ferromagnetic materials presents an important mechanism, namely $\pi $-d electron coupling, to develop magneto-optical and magneto-electronic properties. The $\pi $-d electron coupling has been heavily studied in ground state. This presentation reports the $\pi $-d electron coupling in excited state by combining intramolecular charge-transfer dipoles in semiconducting $\pi $ electron system with spin dipoles from surface-modified magnetic nanoparticles based on organic-magnetic nanocomposites. Our magneto-dielectric studies show that the excited state has a much stronger $\pi $-d electron coupling, as compared to ground state, under photoexcitation. We further study the coupling mechanism by analyzing the line-shape of magneto-dielectric response. We find that increasing the Coulomb interactions between electrical dipoles and spin dipoles causes a line-shape narrowing. On contrast, increasing the spin interactions between them leads to a line-shape broadening. As a result, we conclude that the long-range Coulomb interactions and short-range spin interactions are responsible for realizing strong $\pi $-d electron coupling in excited state in organic-magnetic nanocomposites.