A5017500940- Organic Electronics and Photovoltaics
- Radical Photochemical Reactions
- Conducting polymers and applications
- Photochemistry and Electron Transfer Studies
- Electrochemical Analysis and Applications
- Free Radicals and Antioxidants
- Organic Light-Emitting Diodes Research
- Molecular Junctions and Nanostructures
- Spectroscopy and Quantum Chemical Studies
- Advanced Photocatalysis Techniques
- Semiconductor materials and devices
- Electrochemical sensors and biosensors
- Physics of Superconductivity and Magnetism
- Sulfur-Based Synthesis Techniques
- Quantum and electron transport phenomena
- Solid-state spectroscopy and crystallography
- Ammonia Synthesis and Nitrogen Reduction
- Thin-Film Transistor Technologies
- Perovskite Materials and Applications
- Catalytic C–H Functionalization Methods
- CO2 Reduction Techniques and Catalysts
- Advanced Chemical Sensor Technologies
- Advanced Condensed Matter Physics
- Atmospheric chemistry and aerosols
- Mechanical and Optical Resonators
Brookhaven National Laboratory
2013-2024
Brookhaven College
2023
Texas A&M University
2011-2020
American Society For Engineering Education
2020
Wayne State University
2020
Mitchell Institute
2020
University of California, San Diego
2020
Maxim Integrated (United Kingdom)
2020
Washington University in St. Louis
2020
Upton Hospital
2020
Abstract Field‐effect transistors based on conjugated polymers are being developed for large‐area electronic applications flexible substrates, but they also provide a very useful tool to probe the charge transport physics of these complex materials. In this review we discuss recent progress in polymer semiconductor materials, which have brought performance and mobility devices levels comparable that small‐molecule organic semiconductors. These new materials enabled deeper insight into...
Abstract Charge transport is investigated in high‐mobility n ‐channel organic field‐effect transistors (OFETs) based on poly{[ N , ′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2), Polyera ActivInk™ N2200) with variable‐temperature electrical measurements and charge‐modulation spectroscopy. Results indicate an unusually uniform energetic landscape of sites for charge‐carrier along the channel transistor as main reason observed...
Here we report the use of pulse radiolysis and spectroelectrochemistry to generate low-valent nickel intermediates relevant synthetically important Ni-catalyzed cross-coupling reactions interrogate their reactivities toward comproportionation oxidative addition processes. Pulse provided a direct means singly reduced [(dtbbpy)NiBr], enabling identification rapid Ni(0)/Ni(II) process taking place under electrolysis conditions. This approach also permitted measurement Ni(I) rates with...
Abstract Carrier mobility in doped conjugated polymers is limited by Coulomb interactions with dopant counterions. This complicates studying the effect of dopant's oxidation potential on carrier generation because different dopants have polarons polymer backbone. Here, dodecaborane (DDB)‐based are used, which electrostatically shield counterions from carriers and tunable redox potentials at constant size shape. DDB produce mobile due to spatial separation counterion, those greater energetic...
Understanding the electronic structure of organic-organic heterointerfaces is crucial for many device applications organic semiconductors. Here we have developed a simple analytical model to describe effect static dipolar disorder in polymer dielectric on density states an adjacent semiconductor. The degree energetic varies strongly with distance from interface. Using mobility model, been able explain quantitatively both magnitude as well gate voltage dependence field-effect dielectrics...
Non-natural photoenzymatic reactions reported to date have depended on the excitation of electron donor-acceptor complexes formed between substrates and cofactors within protein active sites facilitate transfer. While this mechanism has unlocked new reactivity, it limits types that can be involved in area catalysis. Here we demonstrate direct flavin hydroquinone "ene"-reductase enables participate reactions. We found by using photoexcitation these enzymes gain ability reduce acrylamides...
The nature of interchain π-system contacts, and their relationship to hole transport, are elucidated for the high-mobility, noncrystalline conjugated polymer C16-IDTBT by application scanning tunneling microscopy, molecular dynamics, quantum chemical calculations. microstructure is shown favor an unusual packing motif in which paired chains cross-over one another at near-perpendicular angles. By linking mesoscale microstructural features, revealed coarse-grained dynamics previous studies,...
The emission characteristics and external quantum efficiencies of ambipolar polymer light-emitting field-effect transistors are investigated as a function applied voltage, current density, ratio hole to electron mobility. Green-emitting poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) with balanced mobilities red-emitting poly((9,9-dioctylfluorene)-2,7- diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) strongly unbalanced semiconducting emissive...
While heteroatom-centered radicals are understood to be highly electrophilic, their ability serve as transient electron-withdrawing groups and facilitate polar reactions at distal sites has not been extensively developed. Here, we report a new strategy for the electronic activation of halophenols, wherein generation phenoxyl radical via formal homolysis aryl O–H bond enables direct nucleophilic aromatic substitution halide with carboxylate nucleophiles under mild conditions. Pulse radiolysis...
Polymer light-emitting field-effect transistors (LEFETs) require high and balanced electron hole mobilities to achieve current densities. Here we demonstrate a novel gate dielectric for polymer LEFETs that enables of 0.01cm2∕Vs both electrons holes. The low-k polycyclohexylethylene is placed in direct contact with the poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) semiconductor. A second layer comprising high-k material poly(vinylidene fluoride-trifluoroethylene) used apply electric field...
Understanding the mechanisms limiting ambipolar transport in conjugated polymer field-effect transistors (FETs) is of both fundamental and practical interest. Here, we present a systematic study comparing hole electron charge an polymer, semicrystalline poly(3,3${}^{\ensuremath{'}\ensuremath{'}}$-di-$n$-decylterselenophene) (PSSS). Starting from detailed analysis device characteristics temperature/charge-density dependence mobility, interpret difference between through Vissenberg-Matters...
Ammonia synthesis from N,N,O,O-supported manganese(V) nitrides and 9,10-dihydroacridine using proton-coupled electron transfer visible light irradiation in the absence of precious metal photocatalysts is described. While reactivity nitride correlated with increased absorption blue light, excited-state lifetimes determined by transient were on order picoseconds. This eliminated manganese as responsible for bimolecular N-H bond formation. Spectroscopic measurements hydrogen source,...
The high-frequency mobility of positive charges (holes) moving along the backbones an extensive data set 7 oligomers (n = 2–16) and 6 polymers (⟨n⟩ 26–138) fluorene was measured using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) in benzene. As expected, at 8.9 GHz, isotropic ac mobility, μac,measiso, observed to be strongly dependent on lengths chains due encountering chain ends during one cycle. Values ranged from 5 × 10–4 cm2/(V s) for n 2 repeat unit oligomer 0.18 a...
Dual IrIII/LnNiII metallaphotoredox catalyzed C(sp3)–C(sp2) cross-coupling reactions are widely assumed to proceed by photoinduced single electron transfer steps due the highly oxidizing IrIII* excited state (IrIII = [Ir(dF(CF3)ppy)2(dtbbpy)]+[PF6]−; dF(CF3)ppy 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; Ln dtbbpy 4,4′-di-tert-butyl-2,2′-bipyridine). Using time-resolved absorption and emission spectroscopy, we reveal that energy between various LnNiII precatalysts intermediates with...
Abstract Brillouin spectroscopy has been used to determine the hypersonic velocities, phonon lifetimes, elastic constants and pockels (strain-optic) coefficients of pivalic acid in its plastic crystal phase at a frequency order 109 Hz. The 25°C are C 11 = (3·43 ± 0·04), 12 (1·38 0·06) 44 (0·642 0·003) units 1010 dynes cm-2 §, vary little with temperature. |P 12| (1·330 0·010), 44| (0·210 - P (0·348 0·012). This is thought be first determination for by scattering method. High resolution...
We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in narrow gap semiconductor material $n$-InAs as a function temperature, doping, and pump wavelength. The results are consistent with D'Yakonov-Perel mechanism for temperatures between 77 300 K. However, data suggest that electron-electron scattering should be taken into account determining dependence lifetime on carrier concentration range...
The nature of electron and hole polarons on poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (pF) a copolymer poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) has been studied by chemical doping, pulse radiolysis, charge modulation spectroscopy, quantum calculations, microwave conductivity. While pF exhibits very similar behavior in all respects for the hole, this paper explores hypothesis that donor acceptor (push–pull) F8BT will tend to localize charges. Optical...
We have used time resolved spectroscopy to measure the relaxation of spin polarization in InSb/AlInSb quantum wells (QWs) as a function temperature and mobility. The results are consistent with D'yakonov–Perel (DP) mechanism for high mobility samples over range from 50 300 K. For low at Elliott–Yafet DP mechanisms become comparable. show that can certain circumstances determine which is dominant, above 1 m2 V−1 s−1 20 nm wide InSb QWs it mechanism. also give criterion maximum lifetime terms...
Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the traps. Intramolecular singlet exciton transport to was examined by steady state fluorescence for 17–127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), p-xylene. End capture (CT) all polymer lengths solvents. The CT nature end-trapped is confirmed their...
Triplet excitons created in poly-2,7-(9,9-dihexyl)fluorene (pF) chains with end trap groups solution are efficiently transported to and captured by the groups. The triplets explore entire lengths of chains, even for ∼100 nm long enabling determination completeness end-capping. results show that continuous: they may contain transient barriers or traps, such as those from fluctuations dihedral angles, but free major defects stop motion triplets. Quantitative determinations aided addition a...
Abstract The electron acceptor F4TCNQ p‐dopes aggregates “nanowires” of poly(3‐hexylthiophene) in nonpolar solvents but does not dope unaggregated chains. standard free energy change for the charge transfer to form an ion pair is Δ G ° et = ‐0.21 eV. dissociation constant produce ions toluene by DC conductivity K d 1 × 10 ‐8 ± 50% (Δ 0.48 0.05 eV). This remarkably large , such a low polarity medium, may reflect interchain delocalization hole. particular characteristics this material system...