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Schuster, Nathaniel J.

Publications and source records attributed to Schuster, Nathaniel J..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Tuning the Mobility of Indacenodithiophene-Based Conjugated Polymers via Coplanar Backbone Engineering

Conjugated polymers based on indacenodithiophene-benzothiadiazole (IDT-BT) have attracted great interest due to their high charge carrier mobilities while being low crystallinity (i.e. near-amorphous.) They represent a promising design strategy to achieve both excellent stretchability and electrical performance. Here, we describe an approach on structural modifications of IDT-BT, namely by introducing non-covalent interactions and substituting building blocks to promote extended coplanar backbones. We systematically investigated the effects of structural modifications on backbone conformation, polymer aggregations, and charge carrier mobilities. Among the investigated polymers, the fluorinated derivative IDT-FBT demonstrated the highest charge carrier mobility of 5.19 cm 2 /Vs, along with low activation energy and Urbach energy indicating its low energy disorder level. The high mobility was attributed to the higher backbone planarity reinforced by S···F and H···F non-covalent interactions and improved interchain interactions through strong aggregation. In conclusion, our findings indicate that increasing backbone coplanarity may further improve mobility in low crystallinity conjugated polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chirality Amplified: Long, Discrete Helicene Nanoribbons

Here we report the synthesis of two polyhelicene frameworks consisting, from end-to-end, of 18 and 24 fused benzene rings. The latter exhibits the largest electronic circular dichroism in the visible spectrum of any molecule. These shape-persistent helical nanoribbons incorporate multiple helicenes, a class of contorted polycyclic aromatic molecules consisting of ortho-annulated rings. These conjugated, chiral molecules have interesting chemical, biological, and chiroptical properties; however, there are very few helicenes with extraordinary chiroptical response over a broad range of the visible spectrum—a key criterion for applications such as chiral optoelectronics. In this report, we show that coupling the polyhelicene framework with multiple perylene-diimide subunits elicits a significant chiroptic response. Notably, the molar circular dichroism increases faster than the absorptivity of these molecules as their helical axis lengthens. Computational analysis reveals that the greatly amplified circular dichroism arises from exciton-like interactions between the perylene-diimide and the helicene moieties. As a result, we predict that even greater chiroptic enhancement will result from further axial elongation of these nanoribbons, which can be readily enabled via the iterative synthetic method presented herein.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The Structural Origins of Intense Circular Dichroism in a Waggling Helicene Nanoribbon

We report the synthesis of a new perylene-diimide-based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule. Here, this nanoribbon also displays a substantial increase in molar circular dichroism relative to a smaller helical analogue, even though they share a similar structure: both nanoribbons incorporate two conformationally dynamic double-[4]helicene termini and a rigid [6]helicene-based core within their helical superstructures. Using DFT and TDDFT calculations, we find that the double-[4]helicenes within both nanoribbons orient similarly in solution; as such, conformational differences do not account for the disparities in circular dichroism. Instead, our results implicate the configuration of the double-[6]helicene within the larger nanoribbon as the source of the observed chiroptical amplification.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Anthracene Diphosphate Ligands for CdSe Quantum Dots; Molecular Design for Efficient Upconversion

Quantum dot (QD)-sensitized photon upconversion follows a multi-step energy transfer process from the QD to transmitter ligand to a soluble annihilator. Using a novel 10-R-anthracene-1,8-diphosphoric acid (R = octyl, 2- hexyldecyl, phenyl) ligand with high binding affinity for CdSe QD surfaces, we demonstrate a photon upconversion process that is limited by the transmitter to annihilator transfer efficiency. Using 1 H NMR spectroscopy, we demonstrate that these bidentate diphosphate ligands rapidly and irreversibly displace two carboxylate ligands. These ligands mediate energy transfer from the photoexcited QDs to a triplet annihilator (1,10-diphenylanthracene), producing overall photon upconversion quantum efficiencies as high as 17%, the highest for QDs with no shells. In conclusion, transient absorption spectroscopy shows that the anthracene dihydrogen phosphate (ADP) ligand supports a 3.4 fold longer triplet state lifetime compared to 9-anthracene carboxylic acid (299.9 ± 9.5 vs 88.2 ± 2.1 μs), increasing the probability of energy transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗