Build 3D Nanoparticles by Using Ultrathin 2D MOF Nanosheets for NIR Light-Triggered Molecular Switching

Abstract

The coordination interactions between transitionmetal ions (Cu 2+ , Ag + ) and sulfur atoms on ultrathin twodimensional (2D) nanosheets of spin-crossover (SCO) metal− organic frameworks {[Fe(1,3-bpp) 2 (NCS) 2 ] 2 } n (1,3-bpp = 1,3di(4-pyridyl)propane), which constructed the ultrathin 2D nanosheets into three-dimensional (3D) nanoparticles, have made a profound effect on the SCO performance. Compared with 2D nanosheets, both the intraligand π−π* transition band and the metal-to-ligand charge transition band from the d(Fe) + π(NCS) to π*(1,3-bpp), for the 3D nanoparticles, have shown dramatic blue-shifts; meanwhile, the d−d transition band for the high-spin (HS) state Fe(II) ions has been generated, suggesting significantly the influence of 3D assemble-caused dimensional changes on the solidstate SCO performance of ultrathin 2D nanosheets. More importantly, by loading on the ytterbium ion (Yb 3+ )-sensitized hexagonal phase upconverting nanoparticles in the aqueous colloidal suspension, the near infrared (NIR) light (980 nm) triggered HS (high spin) to LS (low spin) state transitions have been observed, demonstrating the achievement of challenging target of NIR lighttriggered molecular conversion under environment conditions.

Atmospheric humidity-triggered reversible spin-state switching

“…3a shows that the confinement in the sponge has improved three times the intensity of the metal-to-ligand charge transfer (MLCT) bands for 2D-SCO (550–700 nm), which matches well with the energy of the green up-converting light (UCL) from the UCNPs irradiated with a 980 nm laser. 36–38 These results have demonstrated significantly the superiority of the sponge for photo-triggered spin-state switching. Note that, compared with 2D-SCO in the sponge, a further increase of the MLCT bands has been observed for 2D-SCO@UCNPs in the sponge, which was accompanied by a decrease of the d–d transition bands (at around 480 nm) for the LS state Fe( ii ) species (Fig.…”

“…1. 2D-SCO, UCNPs, 2D-SCO@UCNPs, and the naked sponge were prepared according to our previous work; [31][32][33][34][35][36] their transmission electron microscopy (TEM) images are presented at the bottom of Fig. 1.…”

“…The preparation of 2D-SCO@UCNPs was reported in our previous work. [35][36][37][38] Preparation of the naked sponge To a 50 mL three-necked ask with PEG-6000 (0.45 g), 15 mL of DMF was added, which was ultrasonicated for 10 min to completely dissolve. Then 2 g of PVDF was added slowly and the resulting mixtures were stirred for 3 h to get a clear solution.…”

2-D spin crossover materials at the nanometric scale: the effects of the size-reduction on the magnetic properties

“…These hybrid systems might be promising for near infrared (NIR) light-triggered molecular switching applications under ambient conditions. In a recent report, 50 three dimensional (3-D) nanoparticles were synthesized by combining the, previously mentioned, 2-D SCO Fe II nanosheets with transition metal ions (Cu II , Ag I ). The copper and silver ions were selected as they create strong coordination bonds with the sulfur atoms on both surfaces of the nanosheets.…”

Metal–organic framework nanosheets: from nano-scale to micron-scale with tunable color

“…In our group, the preparation of MONs with a single-layer limit, for functional adjustment and various applications, has been performed. 32–38 More recently, by quantitatively breaking the inter-layer halogen-bonding contacts through variations in ultrasonic duration and solvent polarity, for the same MONs, both the 2D nanosheets with lateral size larger than 500 nm and the one-dimensional (1D) nanoribbons with a lateral size smaller than 100 nm, can be obtained. 39 More importantly, the transformation from paramagnetic behavior to antiferromagnetic behavior, triggered by 3D-to-2D evolution, has been observed on MONs.…”