Photomagnetic Carbon Nanotubes at Ambient Conditions

Abstract

Bis(2,2-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (Ru(bpy)2(phen-NH2)2+), an MLCT complex, has a long-lived triplet state in water (λex: 473 nm; λem: 620 nm; τ = 615 ns; Φ = 1 relative to that of Ru(bpy)32+) and a structure analogous to Ru(bpy)32+. When Ru(bpy)2(phen-NH2)2+ was subjected to diazotization in the presence of carbon nanotubes (CNTs), it formed nanodots on the CNTs, rendering the resulting tubes (Ru@CNT) capable of transducing photo stimuli (473 nm) into electricity and magnetism at ambient conditions. The increased functionality was highly reproducible, as evidenced by conductive-mode AFM, vibrating sample magnetometry (VSM), and AC susceptibility analysis. The local magnetism probing of the Ru@CNT with magnetic-mode AFM techniques (MFM) indicated that the magnetism originated from the unpaired electrons formed on the photoexcited nanodots. The resulting phase shift behaved as a function of the luminous power and the voltage (Vb) of the electrical bias applied to the Ru@CNT. The Vb dependence deviated from the expected quadratic correlation, confirming that the formation of the photoinduced charge separation state at the nanodots is responsible for the photomagnetism. The Ru@CNT tubes showed mobility toward external magnets (65 G) when floating on water and under 473 nm illumination. The Ru@CNT thus appears to be a multifunctional material that might be useful in spintronics.