Synthesis of NIR‐Emitting InAs‐Based Core/Shell Quantum Dots with the Use of Tripyrazolylarsane as Arsenic Precursor

Abstract

arsenic precursor [2,16] besides the less reactive tris(trimethylgermyl)arsane (As(GeMe 3 ) 3 ) [17] or highly toxic arsine gas (AsH 3 ). [18] Recently, Srivastava et al. [19] and Grigel et al. [20] highlighted tris(dimethylamino)arsane (As(NMe 2 ) 3 ) as commercially available pre cursor for the facile synthesis of InAs QDs. Mechanistically, As(NMe 2 ) 3 undergoes a transamination reaction with the solvent and reagent oleylamine (OLAH) to give trioleyl arsane (As(OLA) 3 ) under the release of three equivalents of flammable dimethylamine. The reaction of As(OLA) 3 with indium(III) chloride (InCl 3 ) to InAs QDs does not proceed without the subsequent addition of a reducing agent for which typically diisobutylaluminum hydride (DIBALH) [19] and nowadays also trioleylphosphane (P(OLA) 3 ) [20] or a N,Ndimethylethylamine com plex (DMEAAlH 3 ) [21] are used. In the case of DIBALH and DMEA AlH 3 , the As-N bonds are cleaved to give in situ (OLA) x AsH 3x species which react with the indium precursor to InAs QDs. [22,23] With the applied concentration of DIBALH the size of InAs QDs can be tuned according to the method by Srivastava et al. [19] By contrast, the approach by Grigel et al. [20] applies in situ generated P(OLA) 3 as reducing agent for the InAs QD synthesis (Scheme 1). This species is known to act both, as a remarkably efficient phos phorus precursor and reducing agent for the preparation of InP QDs. [24][25][26] Grigel et al. [20] pointed out that phase pure InAs QDs are obtained since P(OLA) 3 only provides the electrons required for the reduction of As(OLA) 3 to InAs (Scheme 1).In previous work we introduced tripyrazolylphosphanes (P(pyr) 3 , e.g., pyr = 3,5dimethylpyrazole, 2) for the convenient preparation of a long term stable (>6 months) P(OLA) 3 stock solution and its application for the synthesis of highly emitting InP/ZnS QDs. [5,6] Derivatives of P(pyr) 3 are accessible on a multigram scale and represent a safe to handle, less toxic sur rogate for cancerogenic hexaalkylphosphorous triamide deriva tives such as trisdimethylaminophosphane (P(NMe 2 ) 3 ) and tris diethylaminophosphane (P(NEt 2 ) 3 ). Moreover, the release of cor rosive, flammable, and gaseous dialkylamines (Me 2 NH, Et 2 NH) during the transamination with OLAH is prevented. The released pyrazoles can easily be recovered in high yields (>94%) and reused for the precursor synthesis. The tripyrazolylarsane (As(pyr) 3 , e.g., pyr = 3,5dimethylpyrazole, 1) analogues are envisioned to react similarly, thus, representing a convenient to handle and stable arsenic precursor for the InAs QD synthesis. Tris(3,5-dimethylpyrazolyl)arsane (1) is introduced as a low-cost and convenient to handle arsenic precursor for the straight forward synthesis of InAs quantum dots (QDs). Transamination of 1 with the solvent oleylamine (OLAH) gives trioleylarsane (As(OLA) 3 ) which in the presence of the reducing agents diisobutylaluminum hydride (DIBAL-H) or trioleylphosphane (P(OLA) 3 ) yields InAsQDs via a typical hot injection approach. The size of the obtain...

ZnCl2 Mediated Synthesis of InAs Nanocrystals with Aminoarsine

“…This result, which sets a new record in the PL efficiency of InAs@ZnSe NCs made by amino-As, is quite surprising as the lattice mismatch between InAs and ZnSe is around 6%, and this high value commonly leads to strained core@shell structures. 25,30,31 Instead, in our peculiar in situ experimental conditions, the formation of an intermediate In− Zn−Se layer between the InAs core and the ZnSe shell was observed, which is believed to reduce the lattice strain. Our work narrows the gap between InAs NCs made with "greener" amino-As and those synthesized with the more toxic, expensive, and pyrophoric TMS-As/TMGe-As precursors, paving the way to further improvements in the synthesis of this technologically important type of NC.…”

“…34,35 Additionally, the PL quantum yields (QYs) characterizing Cd-free InAs-based core@shell NCs made with TMS-As/TMGe-As, such as InAs@InP@ZnSe NCs, can be as high as 23%, while those synthesized with amino-As (i.e., InAs@ZnSe or InAs@ZnS) could only reach ∼10%. 14,26,30,31 It was noted that ZnCl 2 has been extensively used as an additive in the synthesis of InAs NCs based on amino-As and amino-P, the latter acting as a mild reducing agent. ZnCl 2 is actually believed to trigger the NCs formation by activating the amino-P reducing agent, which would not work otherwise.…”

Semiconductor Nanocrystals Emitting in the Second Near‐Infrared Window: Optical Properties and Application in Biomedical Imaging

“…In another study by Eychmüller and co‐workers, tris(3,5‐dimethylpyrazolyl)arsane was chosen as a low‐cost and efficient arsenic precursor to producer InAs SNCs via a hot injection approach. [ 110 ] By varying the amount of reducing agent or the metal halide, differently sized InAs SNCs were obtained with the emission tunable from 540 to 1200 nm.…”

“…To date, reports on III‐V SNCs with absorption/emission in the NIR‐II window largely focus on InAs SNCs. [ 32,91,109,110 ] Their narrow bandgap allows us to tune their emission over 700–1400 nm range, with an additional advantage that the long‐wavelength emission can be realized from small‐sized nanoparticles, which are more likely to be expelled from the body through renal clearance. [ 63 ] After appropriate shell coating, InAs‐based core/shell SNCs show much higher PLQYs (in the range of 10–90%) than most of the NIR‐II emitting materials including single‐wall carbon nanotubes, rare‐earth nanocrystals, organic dyes, and even silver chalcogenide SNCs.…”

“…[76,91] To date, reports on III-V SNCs with absorption/emission in the NIR-II window largely focus on InAs SNCs. [32,91,109,110] Adv. Optical Mater.…”