Browsing by Author "Wang, Chen-Wen"

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Extremely solvent-enhanced absorbance and fluorescence of carbazole interpreted using a damped Franck-Condon simulation
(2020-03-14)
Wang, Chen-Wen
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Zhu, Chaoyuan
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Lin, Sheng Hsien
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;
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Extremely solvent-enhanced absorption and fluorescence spectra of carbazole were investigated by performing a generalized multi-set damped Franck-Condon spectral simulation. Experimental absorption and fluorescence spectra of carbazole in the gas phase were first well reproduced by performing an un-damped Franck-Condon simulation, but a one-set scaling damped Franck-Condon simulation severely underestimated the intensities of the peaks of experimental absorption and fluorescence spectra of carbazole in n-hexane. Then, a multi-set scaling damped Franck-Condon simulation was proposed and carried out for simulating the extremely solvent-enhanced absorbance and fluorescence, and here, the simulated spectra agreed well with the experimental ones. Five (four) representative solvent-enhanced normal modes corresponding to the combination of ring stretching and ring breathing vibrational motions were determined to be responsible for enhanced absorbance (fluorescence) in n-hexane solution. Furthermore, different scalings were applied to the ground and first-excited states, resulting in different enhancement of absorbance and fluorescence, and this analysis revealed atoms in the carbazole interacting with n-hexane solvent molecules and, hence, leading to different normal-mode vibrational vector patterns in the ground and first-excited states, respectively. Basically, the same conclusion was drawn from a simulation with HF-CIS and the three functionals (TD)B3LYP, (TD)B3LYP-35, and (TD)BHandHLYP. The present multi-set scaling damped Franck-Condon simulation scheme was demonstrated to successfully interpret extremely solvent-enhanced absorbance and fluorescence of carbazole in n-hexane-solvent.
Franck-Condon factors perturbed by damped harmonic oscillators: Solvent enhanced X (1)A(g) <-> A(1)B(1u) absorption and fluorescence spectra of perylene
(2014-08-28)
Wang, Chen-Wen
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Yang, Ling
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Zhu, Chaoyuan
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Yu, Jian-Guo
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Lin, Sheng-Hsien
Damped harmonic oscillators are utilized to calculate Franck-Condon factors within displaced harmonic oscillator approximation. This is practically done by scaling unperturbed Hessian matrix that represents local modes of force constants for molecule in gaseous phase, and then by diagonalizing perturbed Hessian matrix it results in direct modification of Huang-Rhys factors which represent normal modes of solute molecule perturbed by solvent environment. Scaling parameters are empirically introduced for simulating absorption and fluorescence spectra of an isolated solute molecule in solution. The present method is especially useful for simulating vibronic spectra of polycyclic aromatic hydrocarbon molecules in which hydrogen atom vibrations in solution can be scaled equally, namely the same scaling factor being applied to all hydrogen atoms in polycyclic aromatic hydrocarbons. The present method is demonstrated in simulating solvent enhanced X (1)A(g) <-> A(1)B(1u) absorption and fluorescence spectra of perylene (medium-sized polycyclic aromatic hydrocarbon) in benzene solution. It is found that one of six active normal modes v10 is actually responsible to the solvent enhancement of spectra observed in experiment. Simulations from all functionals (TD) B3LYP, (TD) B3LYP35, (TD) B3LYP50, and (TD) B3LYP100 draw the same conclusion. Hence, the present method is able to adequately reproduce experimental absorption and fluorescence spectra in both gas and solution phases. (C) 2014 AIP Publishing LLC.
Franck-Condon simulation for unraveling vibronic origin in solvent enhanced absorption and fluorescence spectra of rubrene
(2017)
Hu, Ying
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Wang, Chen-Wen
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Zhu, Chaoyuan
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Gu, Fenglong
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Lin, Sheng-Hsien
Quantum chemistry calculations at the level of (TD)-DFT plus PCM solvent models are employed for analyzing potential energy surfaces and as a result two local minima with D-2, two local minima with C-2H, and one second-order transition state with D-2H group symmetry are found in both ground S-0 and excited-state S-1 potential energy surfaces. Simulated vibronic coupling distributions indicate that only second-order transition states with D-2H group symmetry are responsible for observed absorption and fluorescence spectra of rubrene and vibrational normal-motions related with atoms on the aromatic backbone are active for vibronic spectra. The Stokes shift 1120 cm(-1) (820 cm(-1)) and vibronic-band peak positions in both absorption and fluorescence spectra in non-polar benzene (polar cyclohexane) solvent are well reproduced within the conventional Franck-Condon simulation. By adding damped oscillator correction to Franck-Condon simulation, solvent enhanced vibronic-band intensities and shapes are well reproduced. Four (three) normal modes with vibration frequency around 1550 cm(-1) (1350 cm(-1)) related to ring wagging plus CC stretching and CH bend motions on the backbone are actually interpreted for solvent enhanced absorption (fluorescence) spectra of rubrene in benzene and cyclohexane solutions.
Franck-Condon simulation for unraveling vibronic origin in solvent enhanced absorption and fluorescence spectra of rubrene
(2017-01-01)
Hu, Ying
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Wang, Chen-Wen
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Zhu, Chaoyuan
;
Gu, Fenglong
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Lin, Sheng-Hsien
Quantum chemistry calculations at the level of (TD)-DFT plus PCM solvent models are employed for analyzing potential energy surfaces and as a result two local minima with D-2, two local minima with C-2H, and one second-order transition state with D-2H group symmetry are found in both ground S-0 and excited-state S-1 potential energy surfaces. Simulated vibronic coupling distributions indicate that only second-order transition states with D-2H group symmetry are responsible for observed absorption and fluorescence spectra of rubrene and vibrational normal-motions related with atoms on the aromatic backbone are active for vibronic spectra. The Stokes shift 1120 cm(-1) (820 cm(-1)) and vibronic-band peak positions in both absorption and fluorescence spectra in non-polar benzene (polar cyclohexane) solvent are well reproduced within the conventional Franck-Condon simulation. By adding damped oscillator correction to Franck-Condon simulation, solvent enhanced vibronic-band intensities and shapes are well reproduced. Four (three) normal modes with vibration frequency around 1550 cm(-1) (1350 cm(-1)) related to ring wagging plus CC stretching and CH bend motions on the backbone are actually interpreted for solvent enhanced absorption (fluorescence) spectra of rubrene in benzene and cyclohexane solutions.
Low-temperature passivation of amorphous-silicon thin-film transistors with supercritical fluids
(2007-07-01)
Tsai, Chih-Tsung
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Liu, Po-Tsun
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Chang, Ting-Chang
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Wang, Chen-Wen
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Yang, Po-Yu
In this letter, supercritical CO2 (SCCO2) fluids technology is employed for the first time to effectively passivate the defect states in hydrogenated amorphous-silicon thin-film transistors (a-Si:H TFTs) at low temperature (150 degrees C). With the high transport and diffusion properties of SCCO2 fluids, it is proposed to act as a transporter in delivering the H2O molecules into the amorphous-silicon film and repairing defect states by the H2O molecules. In addition, the propyl alcohol is used as the surfactant between nonpolar-SCCO2 fluids and polar-H2O molecules for mingling H2O molecules uniformly with the SCCO2 fluids. After the treatment Of SCCO2 fluids mixed with water and propyl alcohol, the a-Si:H TFT exhibited superior transfer characteristics and lower threshold voltage. The improvement in electrical characteristics could be verified by the significant reduction of density of states in the mobility gap of amorphous-silicon.
Orientation hydrogen-bonding effect on vibronic spectra of isoquinoline in water solvent: Franck-Condon simulation and interpretation
(2016-10-28)
Liu, Yu-Hui
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Wang, Shi-Ming
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Wang, Chen-Wen
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Zhu, Chaoyuan
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Han, Ke-Li
The excited-state orientation hydrogen-bonding dynamics, and vibronic spectra of isoquinoline (IQ) and its cationic form IQc in water have been investigated at the time-dependent density functional theory quantum chemistry level plus Franck-Condon simulation and interpretation. The excited-state orientation hydrogen bond strengthening has been found in IQ: H2O complex due to the charge redistribution upon excitation; this is interpreted by simulated 1: 1 mixed absorption spectra of free IQ and IQ: H2O complex having best agreement with experimental results. Conversely, the orientation hydrogen bond in IQc: H2O complex would be strongly weakening in the S-1 state and this is interpreted by simulated absorption spectra of free IQc having best agreement with experimental results. By performing Franck-Condon simulation, it reveals that several important vibrational normal modes with frequencies about 1250 cm(-1) involving the wagging motion of the hydrogen atoms are very sensitive to the formation of the orientation hydrogen bond for the IQ/IQc:H2O complex and this is confirmed by damped Franck-Condon simulation with free IQ/IQc in water. However, the emission spectra of the IQ and IQc in water have been found differently. Upon the excitation, the simulated fluorescence of IQ in water is dominated by the IQ: H2O complex; thus hydrogen bond between IQ and H2O is much easier to form in the S-1 state. While the weakened hydrogen bond in IQc: H2O complex is probably cleaved upon the laser pulse because the simulated emission spectrum of the free IQc is in better agreement with the experimental results. Published by AIP Publishing.