Browsing by Author "Cheng, Chi-Wen"

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Dual-mode recognition of transition metal ions by bis-triazoles chained pyrenes
(2009-01-21)
Hung, Hao-Chih
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Cheng, Chi-Wen
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Ho, I-Ting
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Chung, Wen-Sheng
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應用化學系
Fluorescent chemosensors 7-10, with variable methylene chain length as spacers between the two triazole methyl ether units, have been synthesized under 'Click' condition, where the bistriazoles are used as the metal ion binding sites and the pyrenes as the fluorophores. Compound 10, having the longest methylene chain among 7-10, shows monomer and excimer fluorescence quenching in acetonitrile toward Ni(2+), Pb(2+), Cu(2+), Hg(2+), and Cr(3+) ions, however, it shows an enhanced monomer but a decreased excimer emission when complexed with Cd(2+) and Zn(2+) ions. (C) 2008 Elsevier Ltd. All rights reserved.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. I. The para-Amino Systems
(2013-03-07)
Huang, Guan-Jhih
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Cheng, Chi-Wen
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Hsu, Hung-Yu
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Prabhakar, Ch.
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Lee, Yuan-Pern
To understand the effects of solvent-solute hydrogen bonding (SSHB) on the excited-state dynamics of two GFP-like chromophores, p-ABDI and p-CFABDI, we have determined the quantum yields for fluorescence (Phi(f)) and the isomerization Z -> E (Phi(ZE)) and the femtosecond fluorescence and transient infrared absorption in selected solvents. The behavior that Phi(ZE) congruent to 45 0.50 in aprotic solvents, such as CH3CN, indicates that the E-Z photoisomerization adopts a one-bond-flip mechanism through the torsion of the exocyclic C=C bond (the tau torsion) to form a perpendicular species (tau similar to 90 degrees) in the singlet excited state followed by internal conversion (IC) to the ground state and partition to form the E and Z isomers with equal probabilities. The observed Phi(ZE) decreased from 0.50 to 0.15-0.28 when CH3CN was replaced with the protic solvents CH3OH and CF3CH2OH. In conjunction with the solvent-independent rapid (<1 ps) kinetics for the fluorescence decay and the solvent-dependent slow (7-20 ps) kinetics for the ground-state recovery, we conclude that the SSHB modifies the potential energy surface for the tau torsion in a way that the IC occurs also for the twisted intermediates with a tau-torsion angle smaller than 90 degrees, which favors the formation of the Z isomers. The possibility of IC induced by torsion of the exocyclic C-C bond (the phi torsion) is also considered but excluded.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. II. The meta-Amino Systems
(2013-03-07)
Cheng, Chi-Wen
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Huang, Guan-Jhih
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Hsu, Hung-Yu
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Prabhakar, Ch.
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Lee, Yuan-Pern
To rationalize the efficient quenching of the fluorescence and the Z -> E photoisomerization of m-ABDI, the meta-amino analogue of the green fluorescent protein (GFP) chromophore, in protic solvents, the femtosecond time-resolved fluorescence and transient infrared (TRIR) spectra of m-ABDI in CD3CN, CH3OH, and CD3OD are determined. For solutions in CD3CN, the fluorescence decay lifetime is similar to 7.9 ns and IR absorption lines near 1513, 1531, 1557, and 1613 cm(-1) of m-ABDI in its electronically excited state were observed with a decay time >5 ns. For solutions in CH3OH, the fluorescence decay is double exponential with time constants of similar to 16 and 62 ps. In addition to IR absorption lines of m-ABDI in its electronically excited state with a decay time of similar to 16 ps, new features near 1513, 1532, 1554, and 1592 cm(-1) were observed to have a rise time of similar to 19 ps and a decay constant of similar to 58 ps, indicating formation of an intermediate. The assignments for the IR spectra of the ground and excited states were assisted with DFT and TDDFT calculations, respectively. We conclude that the torsion of the exocyclic C=C bond (the tau torsion) is responsible for the nonradiative decay of electronically excited m-ABDI in CD3CN. However, in CH3OH and CD3OD, the solute-solvent hydrogen bonding (SSHB) interactions diminish significantly the barrier of the tau torsion and induce a new pathway that competes successfully with the tau torsion, consistent with the efficient fluorescence quenching and the diminished yield for Z -> E photoisomerization. The new pathway is likely associated with excited state proton transfer (ESPT) from the solvent to m-ABDI, particularly the carbonyl group, and generates an intermediate (ESPT*) that is weakly fluorescent.
Excited state dynamics of green fluorescence protein chromophore derivatives investigated with time-resolved fluorescence and transient infrared absorption
(2012-08-19)
Cheng, Chi-Wen
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Hsu, Hung-Yu
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Huang, Guan-Jhih
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Diau, Eric Wei-Guang
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Yang, Jye-Shane
Extrinsic charge traps in disordered organic materials
(2012-10-01)
Lin, Liang-Bih
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Cheng, Chi-Wen
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Dai, Chi-An
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Lee, Yuan-Pern
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應用化學系
The effects of p-diethylaminobenzaldehyde diphenylhydrazone, a 0.22 eV trap, on the charge transport properties of disordered organic materials consisted of a mixture of N,N'-diphenyl N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine and polycarbonate are described. Trap-perturbed, trap-limited, and trap-controlled (trap-to-trap) transports were observed, where the trap is less effective at very low trap concentrations but appears to have increasing trap depth with respect to the concentration increase in the trap-limited regime. Most photocurrent transients showed non-dispersive transport behaviors; however, some were dispersive, especially at low electric fields or near the cross-over region between the trap-limited and trap-controlled transports. Field dependency of the mobilites at the trap-limited regime is higher than that of the trap-controlled regime, suggesting some type of superexchange phenomenon or field induced detrapping for the latter transport. For most known systems, charge transport reaches at a minimum mobility that is higher than anticipated from the trap depth. Analysis of the experimental results by theoretical models based on molecular crystals and disordered materials strongly suggests the influence of disorder but only gives qualitative agreements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757412]
Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye-Sensitized Solar Cells
(2014-07-31)
Hsu, Hung-Yu
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Cheng, Chi-Wen
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Huang, Wei-Kai
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Lee, Yuan-Pern
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Diau, Eric Wei-Guang
By means of femtosecond infrared transient absorption spectra, we measured the interfacial electron-transfer dynamics for benzimidazole-based heteroleptic ruthenium dyes (RIDS, RD12, RD15-RD18) sensitized on TiO2 thin films. For all measurements, the first singlet metal-to-ligand charge-transfer states ((MLCT)-M-1) of the ruthenium complexes were excited at 519 nm and the injected electrons in the conduction band of TiO2 were probed at 4.3 mu m. All transient signals featured two rising components on a femtosecond-picosecond scale due to a two-step electron injection and an offset (N719, RD16-RD18) or a slow-decay (RD5, RD12, and RD15) component on a nanosecond microsecond scale due to a back electron transfer. A complicated two-step kinetic model was derived analytically to interpret the observed two rising components for which the rapid (tau(1) < 300 fs) and slow (tau(2) = 10-20 ps) electron injections arose from the singlet (MLCT)-M-1 and triplet (MLCT)-M-3 states, respectively. The amplitudes of the two electron-injection components (A(1) and A(2)) were controlled by the rate coefficient of the (MLCT)-M-1 --> (MLCT)-M-3 intersystem crossing; the variations of A(1) and A(2) are consistent with the trend of the corresponding Stokes shifts rationalized with a conventional energy-gap law for nonradiative transitions. Compared with the kinetics observed for the N719 dye, the involvement of a benzimidazole ligand in RD dyes had the effect of accelerating the two electron injections, thus improving the short circuit current of the device. RD dyes substituted with fluorine atoms and/or thiophene units in the benzirnidazole ligands showed a retardation of 3MLCT electron injection relative to that of the nonsubstituted RD5 dye. Acceleration of the BET process was observed for the RD5 dye (9 ns), and both fluoro-substituted dyes (14 ns for RD12 and 21 ns for RD15) and thiophene-substituted dyes (nonobservable for RD16-RD18) had significantly retarded BET kinetics. The observed kinetics of the (MLCT)-M-3 electron injection for all RD dyes is satisfactorily simulated with the Marcus theory.
Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye-Sensitized Solar Cells
(2014-07-31)
Hsu, Hung-Yu
;
Cheng, Chi-Wen
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Huang, Wei-Kai
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Lee, Yuan-Pern
;
Diau, Eric Wei-Guang
By means of femtosecond infrared transient absorption spectra, we measured the interfacial electron-transfer dynamics for benzimidazole-based heteroleptic ruthenium dyes (RIDS, RD12, RD15-RD18) sensitized on TiO2 thin films. For all measurements, the first singlet metal-to-ligand charge-transfer states ((MLCT)-M-1) of the ruthenium complexes were excited at 519 nm and the injected electrons in the conduction band of TiO2 were probed at 4.3 mu m. All transient signals featured two rising components on a femtosecond-picosecond scale due to a two-step electron injection and an offset (N719, RD16-RD18) or a slow-decay (RD5, RD12, and RD15) component on a nanosecond microsecond scale due to a back electron transfer. A complicated two-step kinetic model was derived analytically to interpret the observed two rising components for which the rapid (tau(1) < 300 fs) and slow (tau(2) = 10-20 ps) electron injections arose from the singlet (MLCT)-M-1 and triplet (MLCT)-M-3 states, respectively. The amplitudes of the two electron-injection components (A(1) and A(2)) were controlled by the rate coefficient of the (MLCT)-M-1 --> (MLCT)-M-3 intersystem crossing; the variations of A(1) and A(2) are consistent with the trend of the corresponding Stokes shifts rationalized with a conventional energy-gap law for nonradiative transitions. Compared with the kinetics observed for the N719 dye, the involvement of a benzimidazole ligand in RD dyes had the effect of accelerating the two electron injections, thus improving the short circuit current of the device. RD dyes substituted with fluorine atoms and/or thiophene units in the benzirnidazole ligands showed a retardation of 3MLCT electron injection relative to that of the nonsubstituted RD5 dye. Acceleration of the BET process was observed for the RD5 dye (9 ns), and both fluoro-substituted dyes (14 ns for RD12 and 21 ns for RD15) and thiophene-substituted dyes (nonobservable for RD16-RD18) had significantly retarded BET kinetics. The observed kinetics of the (MLCT)-M-3 electron injection for all RD dyes is satisfactorily simulated with the Marcus theory.
Highly Selective Fluorescent Sensors for Hg(2+) and Ag(+) Based on Bis-triazole-Coupled Polyoxyethylenes in MeOH Solution
(2009-12-01)
Hung, Hao-Chih
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Cheng, Chi-Wen
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Wang, Yu-Yun
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Chen, Yu-Jen
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Chung, Wen-Sheng
Fluorescent chemosensors 6-9, with variable length polyoxyethylenes between two triazolylmethyl ether units, have been synthesized under "click" conditions in which the bis-triazoles and polyoxyethylenes were used as metal-ion binding sites and the pyrenes as fluorophores. Of the 15 metal ions screened, the fluorescence of chemosensors 6-9 in methanol solution was found to be selectively quenched by only Hg(2+) and Ag(+). In contrast, the fluorescence of control compound 10, a [(triazol-4-yl)methoxymethyl]pyrene, was quenched by only Hg(2+). These results imply that the recognition of Hg(2+) does not need the cooperation of two triazole groups. Binding constants for the interactions of 6-9 with Ag(+) increased as the chain length of the polyoxyethylene increased. Finally, a very high selectivity of compound 9 towards Hg(2+) in aqueous methanol solution was observed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Highly Selective Fluorescent Sensors for Hg2+ and Ag+ Based on Bis-triazole-Coupled Polyoxyethylenes in MeOH Solution
(2009-12-01)
Hung, Hao-Chih
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Cheng, Chi-Wen
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Wang, Yu-Yun
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Chen, Yu-Jen
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Chung, Wen-Sheng
Fluorescent chemosensors 6-9, with variable length polyoxyethylenes between two triazolylmethyl ether units, have been synthesized under "click" conditions in which the bis-triazoles and polyoxyethylenes were used as metal-ion binding sites and the pyrenes as fluorophores. Of the 15 metal ions screened, the fluorescence of chemosensors 6-9 in methanol solution was found to be selectively quenched by only Hg2+ and Ag+. In contrast, the fluorescence of control compound 10, a [(triazol-4-yl)methoxymethyl]pyrene, was quenched by only Hg2+. These results imply that the recognition of Hg2+ does not need the cooperation of two triazole groups. Binding constants for the interactions of 6-9 with Ag+ increased as the chain length of the polyoxyethylene increased. Finally, a very high selectivity of compound 9 towards Hg2+ in aqueous methanol solution was observed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
PHYS 689-Rovibronic bands of the A(2)B(2) <- (XB1)-B-2 transition of C6H5O and C6D5O detected with cavity ringdown absorption near 1.15-1.32 mu m
(2008-04-06)
Cheng, Chi-Wen
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Witek, Henryk
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
PHYS 689-Rovibronic bands of the A(2)B(2) <- X(2)B(1) transition of C(6)H(5)O and C(6)D(5)O detected with cavity ringdown absorption near 1.15-1.32 mu m
(2008-04-06)
Cheng, Chi-Wen
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Witek, Henryk
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
Rovibronic bands of the (A)over-tilde (2)B(2)<-(X)over-tilde (2)B(1) transition of C(6)H(5)O and C(6)D(5)O detected with cavity ringdown absorption near 1.2 mu m
(2008-10-21)
Cheng, Chi-Wen
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Witek, Henryk
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Lee, Yuan-Pern
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應用化學系
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應用化學系分子科學碩博班
We recorded several rovibronic bands of C(6)H(5)O and C(6)D(5)O in their (A) over tilde (2)B(2)<-(X) over tilde (2)B(1) transitions in the range 1.14-1.31 mu m with the cavity ringdown technique. While the electronic transition is forbidden, several vibronic bands are observed. By comparison of rovibronic contours of observed and simulated bands to determine their types of transition, and by consideration of vibrational wavenumbers of the upper state based on quantum-chemical calculations, we were able to provide vibronic assignments of observed bands and derive several experimental vibrational wavenumbers (given as nu in unit of cm(-1) in this paper) for the (A) over tilde (2)B(2) state, namely, nu(12)=947, nu(13)=793, nu(14)=417, nu(15)=964, nu(16)=866, nu(17)=723, nu(18)=680, and nu(19)=499 for C(6)H(5)O, and nu(12)=772, nu(13)=626, nu(14)=365, nu(15)=812, nu(17)=599, nu(18)=532, and nu(19)=436 for C(6)D(5)O. Transitions involving vibrationally excited levels of nu(20) were also observed; nu(20) of the (A) over tilde state is greater by 50 cm(-1) than the (X) over tilde state of C(6)H(5)O. A weak origin at 7681 cm(-1) for the (A) over tilde <-(X) over tilde transition of C(6)H(5)O (7661 cm(-1) for C(6)D(5)O) with a c-type contour was observed. Observed isotopic ratios of vibrational wavenumbers for the (A) over tilde state of C(6)H(5)O to those of C(6)D(5)O are in good agreement with the predictions from quantum-chemical calculations at the B3LYP/aug-cc-pVTZ level. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2992077]
Rovibronic bands of the (A)over-tilde <-(X)over-tilde transition of CH3OO and CD3OO detected with cavity ringdown absorption near 1.2-1.4 mu m
(2007-07-28)
Chung, Chao-Yu
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Cheng, Chi-Wen
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Lee, Yuan-Pern
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Liao, Hsin-Yi
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Sharp, Erin N.
We have recorded several rovibronic bands of CH3OO and CD3OO in their (A) over tilde <-(K) over tilde transitions in the range of 1.18-1.40 mu m with the cavity ringdown technique. While the electronic origins for these species have been reported previously, many newly observed rovibronic bands are described here. The experimental vibrational frequencies (given as nu in the unit cm(-1) in this paper) for the COO bending (nu(8)) and COO symmetric stretching (nu(7)) modes in the (A) over tilde state are 378 and 887 cm(-1) for CH3OO, and 348 and 824 cm(-1) for CD3OO, respectively. In addition, two other vibrational frequencies were observed for the (A) over tilde state of CD3OO, namely, nu(5) (954 cm(-1)) and nu(6) (971 cm(-1)). These experimental vibrational frequencies for the A state of both CH3OO and CD3OO are in good agreement with predictions from quantum-chemical calculations at the UB3LYP/aug-cc-pVTZ level. The enhanced activity of the nu(5) vibrational mode in CD3OO is rationalized by mode mixing with the nu(7) mode, as supported by calculations of multidimensional Franck-Condon factors. In addition, many hot bands involving the methyl torsional mode (nu(12)) are observed for both normal and deuterated methyl peroxy. These bands include the "typical" sequence transitions and some "atypical" ones due to the nature of the eigenvalues and eigenfunctions which are a consequence of the low, but very different, torsional barriers in the (X) over tilde and (A) over tilde states. In addition, the 12(2)(2) band in CH3OO and the 12(3)(3) band in CD3OO show quite different structures than the origin bands, an effect which results from tunneling splittings comparable to the rotational contour. (C) 2007 American Institute of Physics.
Study of the reactive excited-state dynamics of delipidated bacteriorhodopsin upon surfactant treatments
(2012-06-29)
Cheng, Chi-Wen
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Lee, Yuan-Pern
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Chu, Li-Kang
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應用化學系
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應用化學系分子科學碩博班
The dynamics of the reactive excited-state of bacteriorhodopsin treated with various surfactants have been investigated through the measurement of pump-probe absorption spectra. Upon excitation of bR at 570 nm in the presence of ionic surfactants CTAB and SDS, the lifetime of the reactive excited-state of the all-trans protonated Schiff base, probed at 460 nm, was observed to increase up to 20%, whereas an insignificant change was observed upon addition of neutral surfactant C6E2. Measurements of steady-state absorption spectra, fluorescence, and circular dichroism indicated that the bR suspensions retain their trimeric configuration with partial delipidation. This removal of lipids causes a structural alteration and the varied excited-state dynamics. (C) 2012 Elsevier B. V. All rights reserved.
Synthesis and electron-transfer properties of benzimidazole-functionalized ruthenium complexes for highly efficient dye-sensitized solar cells
(2010)
Huang, Wei-Kai
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Cheng, Chi-Wen
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Chang, Shu-Mei
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Lee, Yuan-Pern
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Diau, Eric Wei-Guang
Novel heteroleptic ruthenium complexes-RD1, RD5, RD10 and RD11-with ligands based on benzimidazole were synthesized and characterized for application to dye-sensitized solar cells (DSSC); the remarkable performance of RD5-based DSSC is understood for its superior light-harvesting ability and slower charge-recombination kinetics.
Theoretical Interpretation of the UV-vis Spectrum of the CS(2)/Cl Complex in the Spectral Region 320-550 nm
(2010-10-21)
Camacho, Cristopher
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Cheng, Chi-Wen
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Witek, Henryk A.
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Lee, Yuan-Pern
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應用化學系
Accurate multireference configuration interaction and time-dependent density functional calculations have been performed to interpret the experimental UV-vis spectrum of the CS(2)/Cl complex in the spectral region 320-550 nm. The molecular structure of the complex responsible for the previously observed UV-vis spectrum is recognized as ClSCS, not CICS(2). Two low-lying excited states of ClSCS, responsible for its optical absorption, have been identified and analyzed. Optical excitation of ClSCS leads to the excitation-specific bond elongation that may lead to photofragmentation of the molecule. In addition, experimental conditions for verifying the presence of ClCS(2) are identified and detailed characterization of its optically active excited states with possible photofragmentation pathways is given.
Theoretical Interpretation of the UV-vis Spectrum of the CS2/Cl Complex in the Spectral Region 320-550 nm
(2010-10-21)
Camacho, Cristopher
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Cheng, Chi-Wen
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Witek, Henryk A.
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Lee, Yuan-Pern
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應用化學系
Accurate multireference configuration interaction and time-dependent density functional calculations have been performed to interpret the experimental UV-vis spectrum of the CS2/Cl complex in the spectral region 320-550 nm. The molecular structure of the complex responsible for the previously observed UV-vis spectrum is recognized as ClSCS, not CICS2. Two low-lying excited states of ClSCS, responsible for its optical absorption, have been identified and analyzed. Optical excitation of ClSCS leads to the excitation-specific bond elongation that may lead to photofragmentation of the molecule. In addition, experimental conditions for verifying the presence of ClCS2 are identified and detailed characterization of its optically active excited states with possible photofragmentation pathways is given.
Theoretical investigation of molecular properties of the first excited state of the phenoxyl radical
(2008-03-27)
Cheng, Chi-Wen
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Lee, Yuan-Pern
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Witek, Henryk A.
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應用化學系
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應用化學系分子科學碩博班
A theoretical study of molecular, electronic, and vibrational properties of the first excited state of the phenoxyl radical, A B-2(2), is presented. The calculated molecular geometries, vertical and adiabatic excitation energies, and harmonic vibrational frequencies are compared with analogous results obtained for the ground state. The calculated excitation energies correspond well to experimental data. The harmonic vibrational frequencies of the A B-2(2) and the ground state are similar except for modes involving the vibrations of the CO bond.
Theoretical Investigation of Molecular Properties of the First Excited State of the Thiophenoxyl Radical
(2008-11-27)
Cheng, Chi-Wen
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Lee, Yuan-Pern
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Witek, Henryk A.
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應用化學系
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應用化學系分子科學碩博班
Accurate ab initio study of the lowest excited state (A (2)B(2)) of the thiophenoxyl radical is presented. The calculated equilibrium geometries, excitation energies, and harmonic vibrational frequencies show that the A (2)B(2) <- X (2)B(1) excitation in C(6)H(5)S has different characteristics than the analogous transition in the phenoxyl radical. Vertical excitation energies for other low-lying (<4.5 eV) excited states of the thiophenoxyl radical are also presented and compared with available experimental data.