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Hung W.-Y.,National Taiwan Ocean University | Wang T.-C.,National Taiwan University | Chiang P.-Y.,National Taiwan Ocean University | Peng B.-J.,National Taiwan University | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2017

This work reports a new strategy of introducing remote steric effect onto the electron donor for giving the better performance of the exciplex-based organic light-emitting device (OLED). The bulky triphenylsilyl group (SiPh3) was introduced onto the fluorene bridge of 4,4′-(9H-fluorene-9,9-diyl)bis(N,N-di-p-tolylaniline) (DTAF) to create remote steric interactions for increasing the possibility of effective contacts between electron-donating chromophores and acceptor molecules, rendering the resulting exciplex to have a higher photoluminescence quantum yield (PLQY). The green exciplex device based on DSDTAF:3N-T2T (1:1) as an emitting layer exhibits a low turn-on voltage of 2.0 V, high maximum efficiencies (13.2%, 42.9 cd A-1, 45.5 lm W-1), which are higher than the device employed DTAF (without SiPh3 groups) (11.6%, 35.3 cd A-1, 41.3 lm W-1) as donor under the same device structure. This strategy was further examined for blue exciplex, where the EQE was enhanced from 9.5% to 12.5% as the electron acceptor PO-T2T mixed with a tert-butyl group substituted carbazole-based donor (CPTBF) as the emitting exciplex in device. This strategy is simple and useful for developing high performance exciplex OLEDs. © 2017 American Chemical Society.

Mineo H.,Institute of Atomic and Molecular Science | Fujimura Y.,National Chiao Tung University
Journal of Physics: Conference Series | Year: 2015

We propose an ultrafast quantum switching method of π-electron rotations, which are switched among four rotational patterns in a nonplanar chiral aromatic molecule (P)-2,2'- biphenol and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses. Coherent π-electron dynamics are generated by applying the linearly polarized UV pulse laser to create a pair of coherent quasidegenerated excited states. We also plot the time-dependent π-electron ring current, and discussed ring current transfer between two aromatic rings. © Published under licence by IOP Publishing Ltd.

Chen S.-Y.,National Chiao Tung University | Lee Y.-P.,National Chiao Tung University | Lee Y.-P.,Institute of Atomic and Molecular science
Journal of Chemical Physics | Year: 2010

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of CH3 CO and O2; IR absorption spectra of CH3 C (O) OO and α -lactone were observed. Absorption bands with origins at 1851±1, 1372±2, 1169±6, and 1102±3 cm-1 are attributed to t -CH3 C (O) OO, and those at 1862±3, 1142±4, and 1078±6 cm-1 are assigned to c -CH3 C (O) OO. A weak band near 1960 cm-1 is assigned to α -lactone, cyc- CH2 C (=O) O, a coproduct of OH. These observed rotational contours agree satisfactorily with simulated bands based on predicted rotational parameters and dipole derivatives, and observed vibrational wavenumbers agree with harmonic vibrational wavenumbers predicted with B3LYP/aug-cc-pVDZ density-functional theory. The observed relative intensities indicate that t -CH3 C (O) OO is more stable than c -CH3 C (O) OO by 3±2 kJ mol-1. Based on these observations, the branching ratio for the OH+α -lactone channel of the CH3 CO+ O2 reaction is estimated to be 0.04±0.01 under 100 Torr of O2 at 298 K. A simple kinetic model is employed to account for the decay of CH 3 C (O) OO. © 2010 American Institute of Physics.

Zhang B.,University of Texas at San Antonio | Fang C.-Y.,Institute of Atomic and Molecular science | Chang C.-C.,Institute of Atomic and Molecular science | Peterson R.,University of Texas at San Antonio | And 4 more authors.
Biomedical Optics Express | Year: 2012

Fluorescent nanodiamonds (FNDs) have drawn much attention in recent years for biomedical imaging applications due to their desired physical properties including excellent photostability, high biocompatibility, extended far-red fluorescence emission, and ease of surface functionalization. Here we explore a new feature of FNDs, i.e. their photoacoustic emission capability, which may lead to potential applications of using FNDs as a dual imaging contrast agent for combined fluorescence and photoacoustic imaging modalities. We observed significant enhancement of photoacoustic emission from FNDs when they were conjugated with gold nanoparticles (GNPs). © 2012 Optical Society of America.

Chu J.-F.,Institute of Atomic and Molecular science | Chu J.-F.,National Taiwan Normal University | Chang T.-C.,Institute of Atomic and Molecular science | Chang T.-C.,National Taiwan University | Li H.-W.,National Taiwan University
Biophysical Journal | Year: 2010

Human telomere contains guanine-rich (G-rich) tandem repeats of single-stranded DNA sequences at its 3′ tail. The G-rich sequences can be folded into various secondary structures, termed G-quadruplexes (G4s), by Hoogsteen basepairing in the presence of monovalent cations (such as Na + and K+). We developed a single-molecule tethered particle motion (TPM) method to investigate the unfolding process of G4s in the human telomeric sequence AGGG(TTAGGG)3 in real time. The TPM method monitors the DNA tether length change caused by formation of the G4, thus allowing the unfolding process and structu ral conversion to be monitored at the single-molecule level. In the presence of its antisense sequence, the folded G4 structure can be disrupted and converted to the unfolded conformation, with apparent unfolding time constants of 82 s and 3152 s. We also observed that the stability of the G4 is greatly affected by different monovalent cations. The folding equilibrium constant of G4 is strongly dependent on the salt concentration, ranging from 1.75 at 5 mM Na+ to 3.40 at 15 mM Na +. Earlier spectral studies of Na+- and K +-folded states suggested that the spectral conversion between these two different folded structures may go through a structurally unfolded intermediate state. However, our single-molecule TPM experiments did not detect any totally unfolded Intermediate within our experimental resolution when sodium-folded G4 DNA molecules were titrated with high-concentration, excess potassium ions. This observation suggests that a totally unfolding pathway is likely not the major pathway for spectral conversion on the timescale of minutes, and that interconversion among folded states can be achieved by the loop rearrangement. This study also demonstrates that TPM experiments can be used to study conformational changes in single-stranded DNA molecules. © 2010 by the Biophysical Society.

Dvoynenko M.M.,Ukrainian Academy of Sciences | Dvoynenko M.M.,Institute of Atomic and Molecular science | Wang J.-K.,National Taiwan University | Wang J.-K.,Institute of Atomic and Molecular science
Optics Letters | Year: 2013

Strong coupling between a single molecule and surface plasmons is reexamined with a microscopic classical formulation in local and nonlocal responses of metal. In the case of local response, we show that strong single molecule-plasmon coupling can occur in the UV range for a silver particle with a molecule-metal separation of 1 nm or smaller, where the real part of the dielectric function of silver approaches -1. With the nonlocal response consideration, strong coupling happens at shorter molecule-metal distances. The result shows that Rabi splitting can occur even without a resonator. © 2013 Optical Society of America.

Nayak A.P.,University of Texas at Austin | Pandey T.,Indian Institute of Science | Voiry D.,Rutgers University | Liu J.,University of Texas at Austin | And 10 more authors.
Nano Letters | Year: 2015

Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure-property relation due to the rich band structure of MoS2. Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibrational properties of the MoS2 family can be extended to other 2D TMDs. These results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications. © 2014 American Chemical Society.

Takahashi K.,University of Colorado at Boulder | Takahashi K.,Institute of Atomic and Molecular science | Plath K.L.,University of Colorado at Boulder | Axson J.L.,University of Colorado at Boulder | And 3 more authors.
Journal of Chemical Physics | Year: 2010

The early time dynamics of vibrationally excited glyoxylic acid and of its monohydrate 2,2-dihydroxyacetic acid are investigated by theoretical and spectroscopic methods. A combination of "on-the-fly" dynamical simulations and cavity ring-down spectroscopy on the excited O-H stretching vibrational levels of these molecules observed that conformers that possess the correct structure and orientation react upon excitation of Δ v OH =4,5, while the structurally different but near isoenergetic conformers do not undergo unimolecular decay by the same direct and fast process. Experiment and theory give a femtosecond time scale for hydrogen atom chattering in the vibrationally excited glyoxylic acid. This process is the precursor for the concerted decarboxylation of the ketoacid. We extrapolate the results obtained here to suggest a rapid subpicosecond overall reaction. In these light-initiated reactions, relatively cold hydroxycarbenes, stable against further unimolecular decay, are expected products since most of the excitation energy is consumed by the endothermicity of the reaction. Glyoxylic acid and its monohydrate are atmospherically relevant ketoacids. The vibrational overtone initiated reactions of glyoxylic acid leading to di- and monohydroxycarbenes on subpicosecond time scales are potentially of importance in atmospheric chemistry since the reaction is sufficiently rapid to avoid collisional dissipation. © 2010 American Institute of Physics.

Kumar P.,Institute of Atomic and Molecular science | Hu L.-H.,Southern Taiwan University of Science and Technology
Journal of Alloys and Compounds | Year: 2016

Flower-like self-assembly of vanadium pentoxide (V2O5) has been synthesized via a facile, eco-friendly and bottom-up approach using hydrothermal process at low temperature with high-yield for the first time. This hierarchical flower-like structure is found to be accumulated with numerous plate-like subunits, and each unit seems to be a complete structure of randomly grown hexagonal nano/micro plates. A possible reaction mechanism for the formation of hierarchical flower-like structures of V2O5 has also been proposed. The reduction process (from V5+to V4+ or some mix oxidation states)is carried out through sulphur-reduction by using an advanced homemade CVD system with argon as the carrier gas at different temperatures. The sulphur reduced V2O5 structure formed shows excellent lithium storage and rate capability. After sulphur-reduction, the specific capacity of the flower-like V2O5 as the cathode material can achieve 400 mAh g-1, 300 mAh g-1, 250 mAh g-1 and 100 mAh g-1 at different rates of 0.07C, 1C, 2.3C and 29 C, respectively between 1.75 V and 4 V. © 2015 Elsevier B.V.

Chen Y.-W.,National Chung Cheng University | Hsu C.-H.,Institute of Atomic and Molecular science | Hsu C.-H.,National Tsing Hua University | Hwang D.W.,National Chung Cheng University
Magnetic Resonance in Medicine | Year: 2014

Purpose The goal of this study is to develop novel MR contrast by frequency lock-in technique. Methods An electronic feedback device that can control the frequency and bandwidth of the feedback RF field is presented. In this study, the effects of lock-in suppressed imaging are discussed both theoretically and experimentally. Results Two important imaging experiments were performed. The first experiment used magnetizations with the same central frequency but different frequency distributions and was compared with MR images obtained with T2 contrast agents. Lock-in suppressed images showed an improvement in contrast relative to the conventional imaging method. The second experiment used magnetizations with small shifts in frequency and a broad frequency distribution. This is helpful for differentiating between small structural variations in biological tissues. The contrast achieved in in vivo tumor imaging using the lock-in suppressed technique provide higher spatial resolutions and discriminate the regimes of necrosis and activation consistent with pathologic results. Conclusion Lock-in suppressed imaging introduces a conceptually new approach to MRI. Heightened sensitivity to underlying susceptibility variations and their relative contribution to total magnetization may thus be achieved to yield new and enhanced contrast. © 2013 Wiley Periodicals, Inc.

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