Luminescent Quantum Dots Stabilized by N-Heterocyclic Carbene Polymer Ligands

Abstract

We have tested the ability of N-heterocyclic carbene (NHC)-modified ligands to coordinate and stabilize luminescent CdSe−ZnS core−shell quantum dot (QD) dispersions in hydrophilic media. In particular, we probed the effects of ligand structure and coordination number on the coating affinity to the nanocrystals. We find that such NHC-based ligands rapidly coordinate onto the QDs (requiring ∼5−10 min of reaction time), which reflects the soft Lewis base nature of the NHC groups, with its two electrons sharing capacity. Removal of the hydrophobic cap and promotion of carbenedriven coordination on the nanocrystals have been verified by 1 H NMR spectroscopy, while 13 C NMR was used to identify the formation of carbene−Zn complexes. The newly coated QD dispersions exhibit great long-term colloidal stability over a wide range of conditions. Additionally, we find that coordination onto the QD surfaces affects the optical and spectroscopic properties of the nanocrystals. These include a size-dependent red-shift of the absorption and fluorescence spectra and a pronounced increase in the measured fluorescence intensity when the samples are stored under white light exposure compared to those stored in the dark.

Beyond a Linker: The Role of Photochemistry of Crosslinkers in the Direct Optical Patterning of Colloidal Nanocrystals

“…By contrast, carbenes have been reported as Lewis bases/ligands that are able to stabilize Cd 2 + or Zn 2 + -metal complexes [20] and passivate II-VI QDs. [21] Unraveling the nature of the photochemical effects of nitrene-and carbene-based crosslinkers needs further studies. Nonetheless, the combination of the benign photo-chemistry of carbene radicals and the high photostability of QDs against 365 nm exposure leads to almost unchanged PLQYs and thereby nearly nondestructive patterning (Figure 4C).…”

Highly Ordered N-Heterocyclic Carbene Monolayers on Cu(111)

“… 1 − 18 The ability of NHCs to produce self-assembled monolayers on a range of metallic, non-metallic, and metalloid substrates has attracted considerable interest with potential applications in multiple fields including catalysis, microelectronics, biosensing, surface protection, and 3D MOF architectures. 1 , 2 , 4 , 10 , 14 , 19 − 23 In such applications, it is critical to control the orientation and packing of NHC monolayers to fine-tune surface density, metal accessibility, and ligand orientation. Although the factors dictating binding orientation and self-assembly are not fully elucidated, several studies have pointed toward the important effect of exocyclic nitrogen substituents (wingtips).…”

Highly ordered N-heterocyclic carbene monolayers on Cu(111)

“…N-heterocyclic carbenes (NHCs) are an emerging class of ligands for functionalizing extended metal surfaces, nanoparticles and nanoclusters. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The ability of NHCs to produce self-assembled monolayers on a range of metallic, non-metallic, and metalloid substrates has attracted considerable interest with potential applications in multiple fields including catalysis, microelectronics, biosensing, surface protection and 3D MOF architectures. [1,2,4,10,14,[17][18][19][20][21] In such applications, it is critical to control the orientation and packing of NHC monolayers to finetune surface density, metal accessibility, and ligand orientation.…”