2 research outputs found
Flexible Polymer-Assisted Mesoscale Self-Assembly of Colloidal CsPbBr<sub>3</sub> Perovskite Nanocrystals into Higher Order Superstructures with Strong Inter-Nanocrystal Electronic Coupling
Surface-passivating ligands, although
ubiquitous to colloidal nanocrystal
(NC) syntheses, play a role in assembling NCs into higher order structures
and hierarchical superstructures, which has not been demonstrated
yet for colloidal CsPbX<sub>3</sub> (X = Cl, Br, and I) NCs. In this
work, we report that functional polyÂ(ethylene glycols) (PEG<sub>6</sub>-Y, Y = −COOH and −NH<sub>2</sub>) represent unique
surface-passivating ligands enabling the synthesis of near-uniform
CsPbBr<sub>3</sub> NCs with diameters of 3.0 nm. The synthesized NCs
are assembled into individual pearl necklaces, bundled pearl necklaces,
lamellar, and nanorice superstructures, <i>in situ</i>.
It is believed a variety of forces, including van der Waals attractions
between hydrophilic PEG tails in a nonpolar solvent and dipole–dipole
attraction between NCs, drive mesoscale assembly to form superstructures.
Furthermore, postsynthetic ligand treatment strengthens the argument
for polymer-assisted mesoscale assembly as pearl necklace assemblies
can be successfully converted into either lamellar or nanorice structures.
We observe an ∼240 meV bathochromic shift in the lowest energy
absorption peak of CsPbBr<sub>3</sub> NCs when they are present in
the lamellar and nanorice assemblies, representing strong inter-NC
electronic coupling. Moreover, pearl necklace structures are spontaneously
assembled into micrometer length scale twisted ribbon hierarchical
superstructures during storage of colloidal CsPbBr<sub>3</sub> NCs.
The results show that the self-assembled superstructures of CsPbBr<sub>3</sub> NCs are now feasible to prepare via template-free synthesis,
as self-assembled structures emerge in the bulk solvent, a process
that mimics biological systems except for the use of nonbiological
surface ligands (PEG<sub>6</sub>-Y). Taken together, emergent optoelectronic
properties and higher order superstructures of CsPbBr<sub>3</sub> NCs
should aid their potential use in solid-state devices and simplify
scalable manufacturing
One-Pot Cascade Approach to PhenÂanthridine-Fused QuiÂnazoÂlinimiÂniums from Heteroenyne-Allenes
A one-pot
cascade method to obtain functionalized phenÂanthriÂdine-fused
quinazoliniminiums from a variety of heteroenyne-allenes is described.
This protocol involves formation of C–N and C–C bonds
in a single step in the presence of a Lewis acid and trace water to
afford pentacyclic title compounds in moderate to good yields