Synthesis and Study of Photothermal Properties of a Mixed-Valence Nanocluster Cu^I/Cu^II with Strong near-Infrared Optical Absorption Supported by 4-tert-Butylcalix[4]arene Ligand

Abstract

The first mixed-valence nanocluster Cu I /Cu II with the highest percentage of Cu II ions was synthesized by using 4-tert-butylcalix[4]arene (Calix4), with the formula DMF 2 ⊂[(CO 3 ) 2-@Cu II 6 Cu I 3 (Calix4) 3 Cl 2 (DMF) 5 (H 3 O)]•DMF (1), as a photothermal nanocluster. Its structure was characterized using single-crystal X-ray diffraction, Fouriertransform infrared spectroscopy, and powder X-ray diffraction. In addition, the charge state and chemical composition of the nanocluster were determined using electrospray ionization spectrometry and X-ray photoelectron spectroscopy (XPS) spectrum. The results of the XPS and X-ray crystallography revealed that there are two independent Cu II and Cu I centers in nanocluster 1 with the relative abundances of 66.6 and 33.3% for Cu II and Cu I , respectively. The nanocluster contains three four-coordinated Cu I ions with a square-planar geometry and six five-coordinated Cu II ions with a square pyramid geometry. The nanocluster shows strong nearinfrared optical absorption in the solid state and excellent photothermal conversion ability (the equilibrium temperature ∼78.2 °C) with the light absorption centers in 286−917 nm over previous reported pentanucleus Cu I 4 Cu II clusters and Cu II compounds.

Monocarboxylate-protected two-electron superatomic silver nanoclusters with high photothermal conversion performance

“…Compared to other silver-based photothermal materials, clusters I–IV show the best temperature increment under 1-sun (0.1 W cm 2 ) by far. 65 Our results suggest that Ag clusters can be efficient candidates in various photothermal applications, for instance photothermal anti-counterfeiting, 66 photothermal water evaporation, 67 solar thermoelectric production, 68–72 etc ., strongly encouraging further exploration of Ag NC chemistry in this direction.…”

An ultra-stable CuI12 cluster built from a CuI6 precursor sandwiched by two CuI3-thiacalixarene units for efficient photothermal conversion

“…All the Cu atoms both in Cu 6 and Cu 12 showed the low coordination (2, 3, 4) of a typical Cu I . 26,29,30,40,41 Both Cu 6 and Cu 12 contain a highly similar Cu 6 (2-PyS) 6 core but differ in distortion. The average Cu⋯Cu distance in the “Cu 6 (2-PyS) 6 core” of Cu 12 being 3.251 Å is much larger than that for Cu 6 (2.953 Å), which suggests that the presence of Cu 3 -HTC4A stretched the “Cu 6 (2-PyS) 6 core” on both sides (Fig.…”

“…Photothermal studies on Cu-based coordination compounds mainly involved divalent 46 and mixed valence 41,[47][48][49] 0.8 °C s −1 , respectively, under the same conditions. The maximum temperature of Cu 12 reached 124.5 °C (Fig.…”

“…The overall coordination of three Cu in PSBUs is four-coordination in a tetrahedral arrangement. All the Cu atoms both in Cu 6 and Cu 12 showed the low coordination (2, 3, 4) of a typical Cu I 26,29,30,40,41. Both Cu 6 and Cu 12 contain a highly similar Cu…”

“…Photothermal studies on Cu-based coordination compounds mainly involved divalent46 and mixed valence41,[47][48][49] clusters, and a pure Cu I analogue is rarely involved. The larger band gaps originated from LMCT and LLCT as well as the ultrastable nature of Cu 12 prompted us to investigate the photothermal properties.…”