Direct Conversion of Hydride- to Siloxane-Terminated Silicon Quantum Dots

Abstract

Peripheral surface functionalization of hydrideterminated silicon quantum dots (SiQD) is necessary in order to minimize their oxidation/aggregation and allow for solution processability. Historically thermal hydrosilylation addition of alkenes and alkynes across the Si−H surface to form Si−C bonds has been the primary method to achieve this. Here we demonstrate a mild alternative approach to functionalize hydride-terminated SiQDs using bulky silanols in the presence of free-radical initiators to form stable siloxane (∼Si−O−SiR 3 ) surfaces with hydrogen gas as a byproduct. This offers an alternative to existing methods of forming siloxane surfaces that require corrosive Si−Cl based chemistry with HCl byproducts. A 52 nm blue shift in the photoluminescent spectra of siloxane versus alkyl-functionalized SiQDs is observed that we explain using computational theory. Model compound synthesis of silane and silsesquioxane analogues is used to optimize surface chemistry and elucidate reaction mechanisms. Thorough characterization on the extent of siloxane surface coverage is provided using FTIR and XPS. TEM is used to demonstrate SiQD size and integrity after surface chemistry and product isolation.

Size-Dependent Photoluminescence Efficiency of Silicon Nanocrystal Quantum Dots

“…Surface oxidation can reduce the QY, but oxidation does not necessarily lead to low PL efficiency. For example, Si nanocrystals embedded in SiO 2 substrates made by ion implantation followed with thermal annealing have exhibited bright PL, , and nanocrystals linked to capping ligands by Si–O and Si–S bonds have also exhibited bright PL with quantum yield similar to alkyl-passivated (Si–C) nanocrystals. ,, …”

“…For example, Si nanocrystals embedded in SiO 2 substrates made by ion implantation followed with thermal annealing have exhibited bright PL, 46,47 and nanocrystals linked to capping ligands by Si−O and Si−S bonds have also exhibited bright PL with quantum yield similar to alkyl-passivated (Si−C) nanocrystals. 9,43,48 For the very small nanocrystals, there is an increasing probability that the exciton will interact with the nanocrystal surface and nonradiative channels such as defects on the surface or vibrational modes of the capping ligands. 49 The probability of finding an exciton outside the nanocrystal depends on its wave function Ψ, which is obtained by solving the timeindependent Schrodinger equation:…”

Ru-Catalyzed Dehydrogenative Silylation of POSS-Silanols with Hydrosilanes: Its Introduction to One-Pot Synthesis

“…Michalska reported that homogeneous and silica-supported rhodium­(I) complexes might be used for the reaction of several silanols with a series of various hydrosilanes . Anderson et al described a direct conversion of hydride-terminated silicon quantum dots mediated by radical initiators . Recently, the Shimada group has reported a pioneering work on the selective synthesis of hydro-substituted siloxanes and SQs by Au-catalyzed dehydrogenative cross-coupling reaction of hydrosilanes with compounds containing silanol groups .…”

“…38 Anderson et al described a direct conversion of hydride-terminated silicon quantum dots mediated by radical initiators. 39 Recently, the Shimada group has reported a pioneering work on the selective synthesis of hydro-substituted siloxanes and SQs by Au-catalyzed dehydrogenative cross-coupling reaction of hydrosilanes with compounds containing silanol groups. 40 Also worthy of note is the comprehensive use of B(C 6 F 5 ) 3 as the catalyst in the processes utilizing silanols 41,42 and alkoxysilanes.…”

Synthesis of Silicon Quantum Dots with Highly Efficient Full-Band UV Absorption and Their Applications in Antiyellowing and Resistance of Photodegradation

“…Fortunately, due to the several silicon sources and rich groups on the surface, silicon quantum dots (SiQDs) present colorful luminescent and absorbent properties by adjusting the groups on SiQDs surface so that they can emit light from blue to red. − Based on their luminescent properties, many applications are possible, such as photostable biological probes, light-emitting diode, alkaline phosphatase detection, etc. But there are no studies on the detailed absorption properties of water-soluble SiQDs with low cost, especially UV absorption and related applications, and their UV absorption mechanism has not been reported to date.…”