Young S. Park

Formation and Evolution of Single-Molecule Junctions

We analyze the formation and evolution statistics of single-molecule junctions bonded to gold electrodes using amine, methyl sulfide, and dimethyl phosphine link groups by measuring conductance as a function of junction elongation. For each link, the maximum elongation and formation probability increase with molecular length, strongly suggesting that processes other than just metal-molecule bond breakage play a key role in junction evolution under stress. Density functional theory calculations of adiabatic trajectories show sequences of atomic-scale changes in junction structure, including shifts in the attachment point, that account for the long conductance plateau lengths observed.

Polymerization of Tellurophene Derivatives by Microwave‐Assisted Palladium‐Catalyzed ipso‐Arylative Polymerization

We report the synthesis of a tellurophene-containing low-bandgap polymer, PDPPTe2T, by microwave-assisted palladium-catalyzed ipso-arylative polymerization of 2,5-bis[(α-hydroxy-α,α-diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC71 BM show PCE values of up to 4.4%. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 µm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon-carbon bonds between the tellurophene and thiophene rings, which results in the red-shift in absorption upon substitution of tellurium for sulfur.

Identifying the Impact of Domain Knowledge and Cognitive Style on Web-Based Information Search Behavior

Although information searching in hypermedia environments has become a new important problem solving capability, there is not much known about what types of individual characteristics constitute a successful information search behavior. This study mainly investigated which of the 2 factors, 1) natural characteristics (cognitive style), and 2) acquired knowledge (domain knowledge) had a stronger influence on search behavior, and what types of impact these had on search activities. To examine search behavior, the search outcome precision, the searching time, the number of URL nodes, and the number of keywords were analyzed and the demographic backgrounds including the searching experience and gender were also measured to discover any correlation with the major variables. The study findings suggest that domain knowledge was not associated with any other search activities but affected only the search precision. Cognitive style meanwhile did not affect search precision but interacted with the searching experience and this interaction affected the total length of searching time. Finally, there was no correlation found between 2 variables: domain knowledge and cognitive style.

Conductance of single cobalt chalcogenide cluster junctions.

Understanding the electrical properties of semiconducting quantum dot devices have been limited due to the variability of their size/composition and the chemistry of ligand/electrode binding. Furthermore, to probe their electrical conduction properties and its dependence on ligand/electrode binding, measurements must be carried out at the single dot/cluster level. Herein we report scanning tunneling microscope based break junction measurements of cobalt chalcogenide clusters with Te, Se and S to probe the conductance properties. Our measured conductance trends show that the Co-Te based clusters have the highest conductance while the Co-S clusters the lowest. These trends are in very good agreement with cyclic voltammetry measurements of the first oxidation potentials and with density functional theory calculations of their HOMO-LUMO gaps.

Prostatic cancer with an unusual presentation: Polymyositis and mediastinal adenopathy

A 67‐year‐old man with prostate cancer presented with acute polymyositis and vocal cord paralysis as a result of mediastinal lymphadenopathy. His clinical course was unusual, with the development of a malignant pleural effusion, supraclavicular adenopathy, and osteolytic bone lesions. Urologic symptoms developed only pre‐terminally, and osteoblastic bone metastases were not documented. This case suggests that prostate cancer need not have a simple natural history.

Synthesis of Polybenzoquinolines as Precursors for Nitrogen-Doped Graphene Nanoribbons†

Graphene nanoribbons (GNRs) represent promising materials for the next generation of nanoscale electronics. However, despite substantial progress towards the bottom-up synthesis of chemically and structurally well-defined all-carbon GNRs, strategies for the preparation of their nitrogen-doped analogs remain at a nascent stage. This scarce literature precedent is surprising given the established use of substitutional doping for tuning the properties of electronic materials. Herein, we report the synthesis of a previously unknown class of polybenzoquinoline-based materials, which have potential as GNR precursors. Our scalable and facile approach employs few synthetic steps, inexpensive commercial starting materials, and straightforward reaction conditions. Moreover, due to the importance of quinoline derivatives for a variety of applications, the reported findings may hold implications across a diverse range of chemical and physical disciplines.

Vincristine, adriamycin, and mitomycin (VAM) therapy for previously treated breast cancer: A preliminary report

Fifteen patients with metastatic breast cancer previously treated with chemotherapy were treated with a regimen consisting of vincristine, Adriamycin, and mitomycin. Eleven patients (73%) responded with three complete and eight partial responses. The median duration of response was eight months. While all four nonresponders died within five months, the median duration of survival of responders was 18 months. Toxicity was significant but tolerable. Thus, this preliminary report suggests that this regimen is active in advanced previously treated breast cancer, providing meaningful remissions with acceptable toxicity.

ipso-Arylative polymerization as a route to π-conjugated polymers: synthesis of poly(3-hexylthiophene)

ipso-Arylative cross-coupling with two 3-hexylthiophene derivatives, (5-bromo-4-hexylthiophen-2-yl)diphenylmethanol and 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol, has been used to prepare poly(3-hexylhiophene) (P3HT) as a model conjugated polymer. P3HT with number-average molecular weights ranging from 8–20 kg mol−1 (Đ 1.4–2.2) was prepared from 5-bromo-4-hexylthiophen-2-yl)diphenylmethanol with a Pd(OAc)2/PCy3/Cs2CO3 catalyst system. Only oligomerization of 2-(5-bromo-4-hexylthiophen-2-yl)propan-2-ol (Mn ≈ 3 kg mol−1) was observed under similar conditions. Studies with model compounds suggest that side reactions involving end-group loss limit ultimate molecular weights.