Materials/Polymer Chemistry

"Polymer chemists study large, complex molecules (polymers) that are built up from many smaller (sometimes repeating) units "

American Chemical Society

"Materials science is a relatively new and very broad field. It involves applications from a number scientific disciplines that contribute to the creation of new materials."

American Chemical Society

Materials and Polymers session has been scheduled for Monday Late Afternoon.

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Monday Late Afternoon

Session 3B - Room NSC 218 - Moderator: Nahyr López Dauphin

3:00 p.m. - 3:20 p.m.

The Assembly of Covalently-Linked Quantum Dot Heterostructures on Metal Oxide Thin Films: Towards the Characterization of Charge-Transfer Dynamics of a Multilayer System

Caitlin McGranahan, David F. Watson

The State University of New York at Buffalo, Department of Chemistry

Semiconductor quantum dots (QDs) are prime candidates as harvesters of light and donors of excited charge carriers for solar energy conversion, due to their size-dependent optical properties and high molar absorption coefficients along with the possibilities to undergo multi-exciton generation and hot carrier extraction. Recent efforts have established the validity of utilizing carbodiimide-mediated coupling chemistry to tether QDs to each other through the formation of an amide bond between capping ligands of two different QDs. This presentation will focus on (1) characterization of covalently-tethered CdS-amide-CdSe and CdSe-amide-CdTe heterostructures on titanium dioxide (TiO2) and zirconium dioxide (ZrO2) thin films and (2) spectroscopic characterization of excited-state charge-transfer processes.

Dynamic quenching of emission was observed in heterostructure-modified thin films, consistent with excited-state charge transfer. Rate constants for photoinduced hole transfer between QDs were estimated to be on the order of 107 s-1 for both systems. CdSe-amide-CdTe heterostructures exhibited bidirectional charge transfer, in which the rate constant for photoinduced electron transfer between QDs was estimated to be on the order of 108 s-1. These results demonstrate that carbodiimide-mediated coupling chemistry can be used to tether one QD to another QD while immobilized on a metal oxide substrate to facilitate extended charge separation of charge carriers.

3:20 p.m. - 3:40 p.m.

Synthesis and self-assembly of poly(styrene-b-solketal acrylate) linear and bottlebrush block copolymers

Darren Smith, Duk Man Yu, Thomas Russell, Javid Rzayev

The State University of New York at Buffalo, Department of Chemistry

Symmetrical ultra-small molecular weight block copolymers (BCPs) of poly(styrene-b-solketal acrylate) (PS-PSA) were synthesized by atom transfer radical polymerization of the corresponding monomers. A series of PS-PSA BCPs with total degrees of polymerization as low as 16 and low dispersities (1.02-1.25) have been prepared. Small-angle x-ray scattering (SAXS) data shows that PS-PSA BCPs with molecular weights under 10,000 g mol-1 do not order; therefore an increase in the segmental interaction parameter (χ) is required for self-assembly to occur. Acid-catalyzed hydrolysis of the solketal group creates an increase in χ value, allowing the ultra-small samples to self-assemble into lamellar morphology, as seen by SAXS analysis. Upon hydrolysis, poly(styrene-b-glycerol acrylate) (PS-PGA) ordered into lamellar microstructures with domain spacings as low as 6.0 nm. Bottlebrush core-shell copolymers (BBCP) have been synthesized by grafting-through methodologies from PS-PSA BCP precursors. Bromide end-group of the PS-PSA BCPs was used to install a norbornene end functionality in two steps, and well-defined BBCP with a core-shell architecture were subsequently synthesized by ring-opening metathesis polymerization of the block copolymer macromonomers. Melt and thin film self-assembly of PS-PSA BBCPs was studied before and after hydrolysis of the solketal groups and compared to that of their linear analogs.

3:40 p.m. - 4:00 p.m.

Light-Controlled Supramolecular Cages and Its Ligand Design

Xiaotong Zhang, Jason Benedict, Timothy Cook, Zoe Marr, Travis Mitchell

The State University of New York at Buffalo, Department of Chemistry

Supramolecular assemblies have been recently developed and applied towards separation and purification processes, trapping hazardous chemicals, stabilization of transition states, and sensing through guest molecule detection. By combining photo-responsive organic linkers with appropriate metal centers, supramolecular assemblies with properties that may be switched on or off in response to visible light may be realized. Our current approach involves the use of diarylethene (DAE) based ligands and palladium salt to form photochromic cages. DAEs, which undergo bond forming cyclization reactions when exposed to light, often exhibit excellent thermal stability of both the ring open and ring-closed forms. Attempts to characterize nanocage formation using pyridyl-based DAEs, which includes a single crystal structure of a M3L6, will be presented. The synthesis and characterization of novel benzaldehyde-based linkers, which can be used to create extended ligands, will also be discussed. Future studies will focus on increasing synthetic yields and producing photoswitchable crystalline solids that may be analyzed using dynamic in situ X-ray diffraction to help elucidate their structure-property relationship.

4:00 pm - 4:20 p.m.

Host-Guest Study Between Aromatic Oligoamide Foldamers and Macrocycles with Paraquat

Tom Sobiech, Yulong Zhong, Yongye Zhao, Bing Gong

The State University of New York at Buffalo, Department of Chemistry

Aromatic oligoamide foldamers adopt crescent-like backbone conformations that enable them to form either helical structures with sufficient oligomer lengths or cyclize into the corresponding macrocycles. These oligoamide foldamers and macrocycles exhibit unique self-association and molecular recognition properties. Coupling of shorter aromatic oligoamides through formation of amide bonds result in longer oligomers. A series of aromatic oligoamides ranging from the monomer to the 16mer are discussed. Taking advantage of the crescent conformation of their non-cyclic oligomer precursors, macrocycles with six to eight residues were synthesized through intramolecular macrocyclization. This series of aromatic oligoamide foldamers as well as their macrocyclic counterparts offer defined shapes with non-deformable, electron-rich cavities that serve as hosts for binding cationic guest molecules. Using 1H-1H NOESY NMR, the guest molecule, oct-paraquat (PF6), was found to bind inside the cavity of these aromatic oligoamides. The stoichiometry of binding was determined by using both NMR and UV-Vis spectroscopy. Here we present the host-guest interactions between hosts based on an octameric aromatic oligoamide foldamer and a hexamer aromatic oligoamide macrocycle with a paraquat salt.