Near-infrared-II photothermal conversion and magnetic dynamic regulation in [Ln3Rad2] aggregation by rigidity modification of nitronyl nitroxide†

Abstract

Radical-metal compounds used as functional materials can be applied to multiple fields such as solar-thermal conversion and ultra-high density data storage. However, the reactivity and instability of organic radicals usually hamper the development and application of radical-metal compounds. Herein, we utilized persistent nitronyl nitroxide to construct two categories of nitronyl nitroxide-Ln compounds, [Gd₃(hfac)₉(NIT4bpym)₂]₂·4CH₂Cl₂·C₆H₁₄ (1-Gd), [Dy₃(hfac)₉(NIT4bpym)₂] (1-Dy) and [Dy₃(hfac)₉(NITPzCH₂IM)₂]·2CH₂Cl₂ (2-Dy) (NIT4bpym = 2,2′-dipyridyl-4-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl); NITPzCH₂IM = [2-(1-methylimidazole)methyl-1-pyrazol]-4-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl) (hfac = hexafluoroacetylacetonate), involving a rare [4f–2p–4f–2p–4f] multi-spin motif with an electron donor–acceptor pattern. Notably, thanks to the rigidity modification of nitronyl nitroxide, prominent enhancement of photothermal conversion efficiency from 56.9% to 74.0% and the magnetic switching phenomenon have been observed with molecular structure transformation from flexibility (2-Dy) to stiffness (1-Dy), offering an avenue for the regulation of the photothermal effect and magnetic dynamics.