Directed Assembly of Quantum Dots Using Brush Block Copolymers for Well-Ordered Nonlinear Optical Nanocomposites

Abstract

We report the directed assembly of quantum dots (QDs) within wellordered photonic nanocomposites using a family of (polynorbornene-graf tpoly(styrene))-block-(polynorbornene-graf t-poly(ethylene oxide)) (PS-b-PEO) brush block copolymers (BBCPs). Cadmium selenide (CdSe) nanoparticles (NPs) modified with 11-mercaptoundecylhydroquinone are selectively incorporated within the PEO domains of the self-assembled BBCPs via strong hydrogen-bonding interactions between the ligands on QDs and PEO brushes of the BBCPs. Wellordered QD arrays were readily created within a periodic lamellar polymer matrix, or one-dimensional photonic crystal, with a widely tunable lattice spacing ranging from 46.2 to up to 145 nm. The loading concentration of the QDs can be up to 30 wt % (15 vol %) while maintaining a well-ordered lamellar morphology, providing an optical gain material platform for the systematic investigation of optical properties. Strong photoluminescence and third harmonic generation from the well-ordered QD arrays were observed via multiphoton excitation using femtosecond (fs) laser light at several optical wavelengths from 700 to 1550 nm.

Application of Bottlebrush Block Copolymers as Photonic Crystals

“…Watkins and co‐workers have demonstrated that BBCPs can accommodate high NP loading concentrations by designing strong, preferential interactions between NPs and one block of a BBCP. These interactions prevent NP aggregation and promote uniform distribution of the NPs in one domain …”

“…Song et al have investigated the incorporation of gold NPs into polystyrene/poly(ethylene oxide) (PS‐ b ‐PEO) BBCPs (Figure ). [55c] Gold NPs with ≈2 nm core diameter supported by 4‐mercaptophenol ligands were utilized, as strong hydrogen‐bond interactions with these ligands allow for the selective incorporation of gold NPs in the PEO domains of these BBCPs. Composite films with NP loadings as high as 67.2 wt% (Au% = 48.4 wt%) could be prepared by drop casting THF solutions of BBCPs and gold NPs.…”

“…The problem of low reflectance was addressed by the Watkins group in a later report, using blends of functionalized zirconium oxide (ZrO 2 ) NPs, which are transparent to visible light, and P t BA‐ b ‐PEO (P t BA = poly( tert ‐butyl acrylate)) BBCPs to form photonic nanocomposites with high refractive index contrast (Δ n ). [55b] The refractive index of the NP/PEO layer increased linearly with NP concentration (Figure A). Although for typical polymeric PCs Δ n ≤ 0.1, the ZrO 2 NP/BBCP nanocomposites reached refractive index contrasts up to Δ n > 0.27 (Figure B).…”

Zinc‐Coordinated Hierarchical Organization of Ligand‐Stabilized Gold Nanoclusters for Chiral Recognition and Separation

“…Additionally, sophisticated design provides superstructures with physicochemical properties, which are not only superior, but also do not arise in the constituent particles. Popular choices include quantum dots, plasmonic metal nanoparticles, and magnetic nanoparticles . These particles exhibit important physical properties related to technological applications, however, they are extremely difficult to synthesize in larger quantities with uniform size, shape, and chemical constituents.…”

Liquid‐to‐solid transitions in nanoparticle‐filled brush block copolymer composites

“…[7][8][9] As a result, the BBCP architecture has been effectively used for the development of next generation photonic materials, metallo-dielectric materials, porous templates, and ordered nanoparticle arrays. [10][11][12][13][14][15] NPs are generally incorporated into the BCP microstructure through either an in-situ reduction of inorganic precursors, or through a co-assembly of the BCP with exsitu synthesized NPs. 3 During co-assembly, NPs can be sequestered into a specific BCP domain through strong intermolecular interactions between surface ligands on the NPs and the polymer chains of a specific block.…”