Sangwon Ko

Thiophene-Rich Fused-Aromatic Thienopyrazine Acceptor for Donor-Acceptor Low Band-Gap Polymers for Otft and Polymer Solar Cell Applications

Thiophene enriched fused-aromatic thieno[3,4-b]pyrazine systems were designed and employed to produce low band gap polymers (Eg = 1.0–1.4 eV) when copolymerized with fluorene and cyclopentadithiophene. The copolymers are mainly investigated for organic thin film transistor and organic photovoltaic applications. Molecular packing in the thin films of these polymers was investigated using Grazing incidence X-ray Scattering. Although both fluorene and cyclopentadithiophene polymers follow similar face to face π–π stacking, the latter polymers show much smaller lamellar d-spacings due to side-chain interdigitation between the lamellae. This lead to the higher charge carrier mobilities in cyclopentadithiophene polymers (up to 0.044 cm2/V.s) compared to fluorene polymers (up to 8.1 × 10−3 cm2/V.s). Power conversion efficiency of 1.4% was achieved using fluorene copolymer in solar cells with a fullerene derivative as an acceptor. Although the cyclopentadithiophene polymers show lower band gaps with higher absorption coefficients compared to fluorene copolymers, but the power conversion efficiencies in solar cells of these polymers are low due to their low ionization potentials.

3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics

We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.

A short and concise synthetic route to (−)-coniceine

Abstract (−)-Coniceine, the simplest framework of indolizidine alkaloids, has been successfully accessed using a route in which ruthenium-catalyzed ring-closing olefin metathesis (RCM) was the key reaction to establish the unsaturated bicyclic lactam system.

Molecular design for improved photovoltaic efficiency: band gap and absorption coefficient engineering

Removing the adjacent thiophene groups around the acceptor core in low band gap polymers significantly enhances solar cell efficiency through increasing the optical absorption and raising the ionization potential of the polymer.

Ruthenium-catalyzed hydroesterification of alkynes and dienes based on a chelation-approach

Abstract Based on a chelation-assistance strategy, efficient hydroesterification of alkynes and dienes has been achieved using ruthenium catalyst without the need of high pressuric external CO atmosphere, and a diverse range of α,β-unsaturated esters and mono-olefinic esters could be obtained with high stereo- and regioselectivity.

Fused aromatic thienopyrazines: structure, properties and function

Recent development of a fused aromatic thieno[3.4-b]pyrazine system and their application in optoelectronic devices are reviewed. Introduction of a fused aromatic unit followed by side chain engineering, dramatically enhanced the charge carrier mobility in thin film transistor devices and mobilities up to 0.2 cm2/Vs were achieved. The optoelectronic properties of these fused aromatic thienopyrazine polymers (Eg = 1.3 to 1.6 eV, HOMO = −4.9 to −5.2 V) were tuned by introduction of various fused aromatic rings within thienopyrazine. By balancing the fundamental properties of these polymers, both high charge carrier mobilities and moderate PCEs in solar cells were achieved. Further, effects of copolymerizing units are discussed. Low band gap semiconducting polymer (Eg ∼ 1 eV) with high field effect mobility (0.044 cm2/Vs) was obtained using cyclopentadithiophene as copolymerizing unit. Finally, a molecular design approach to enhance the absorption coefficients is discussed, which resulted in improved power conversion efficiency in bulk heterojunction solar cells.

Side chain engineering of fused aromatic thienopyrazine based low band-gap polymers for enhanced charge carrier mobility

A strategic side-chain engineering approach leads to the two orders of magnitude enhancement of charge carrier mobility in phenanthrene based fused aromatic thienopyrazine polymers. Hole carrier mobility up to 0.012 cm2/Vs can be obtained in thin film transistor devices. Polymers were also utilized to fabricate bulk heterojunction photovoltaic devices and the maximum PCE obtained in these OPVs was 1.15%. Most importantly, performances of the devices were correlated with thin morphological analysis performed by atomic force microscopy and grazing incidence X-ray scattering.

Binding behaviors of protein on spatially controlled poly[oligo(ethylene glycol) methacrylate] brushes grafted from mixed self-assembled monolayers on gold

Binding behaviors of streptavidin were investigated with different lateral packing densities of biotin-functionalized, non-biofouling pOEGMA brushes, synthesized by surface-initiated polymerization from mixed SAMs with different mole fractions of the polymerization initiator on gold surfaces.

RUTHENIUM-CATALYZED FACILE AEROBIC OXIDATION OF α-HYDROXYCARBONYLS TO 1,2-DICARBONYL COMPOUNDS

ABSTRACT The aerobic oxidation of α-hydroxycarbonyl compounds was efficiently carried out with a ruthenium catalyst [RuCl2(p-cymene)]2 in the presence of a catalytic amount of base to afford 1,2-diketones or α-ketoesters in good to excellent yields.

Direct Patterning and Biofunctionalization of a Large‐Area Pristine Graphene Sheet

Direct patterning of streptavidin and NIH 3T3 fibroblast cells was successfully achieved over a large-area pristine graphene sheet on Si/SiO2 by aryl azide-based photografting with the conventional UV lithographic technique and surface-initiated, atom transfer radical polymerization of oligo(ethylene glycol) methacrylate.