Yanying Zhao

Resonance Raman spectroscopic and theoretical investigation of the excited state proton transfer reaction dynamics of 2-thiopyridone.

The resonance Raman spectra were obtained for both 2-thiopyridone (2TP) and its proton-transfer tautomer 2-mercaptopyridine (2MP) in water solution. Density functional theory (DFT) calculations were carried out to help elucidate their ultraviolet electronic transitions and vibrational assignments of the resonance Raman spectra associated with their B-band absorptions. The nanosecond time-resolved resonance Raman spectroscopic experiment was carried out to further confirm the assignment that the transient species was the ground state 2MP. The different short-time structural dynamics were examined for both 2TP and 2MP in terms of their resonance Raman intensity patterns. The transition barriers between 2TP and 2MP for S(0), T(1), and S(1) states are determined by using (U)B3LYP-TD and CASSCF level of theory computations, respectively. The excited state proton transfer (ESPT) reaction mechanism is proposed and briefly discussed.

Excited state structural dynamics of tetra(4-aminophenyl)porphine in the condensed phase: resonance Raman spectroscopy and density functional theory calculation study.

Resonance Raman spectra (RRs) of tetra(4-aminophenyl) porphine (TAPP) were obtained, and density functional calculations were done to help the elucidation of the photorelaxation dynamics of Soret (B(x) and B(y) band) and Q(y) electronic transitions. The RRs indicate that the photorelaxation dynamics for the S(0) --> S(3) excited electronic state is predominantly along the totally symmetric porphin ring C(beta)=C(beta) + C(m)C(alpha) stretch, C(m)-ph stretch, and simultaneously along the asymmetric nu(C(m)C(alpha))(as) and nu(C(alpha)C(beta))(as) relaxation processes leading to Q(y) while that for S(0) --> S(2) is predominantly along the porphin ring C(beta)=C(beta) + C(m)C(alpha) stretch and simultaneously along the asymmetric nu(C(m)C(alpha))(as) + nu(C(alpha)C(beta))(as) relaxation processes leading to thermal equilibrium in Q(x). The excited state structural dynamics of TAPP determined from RRs shows that internal conversion B(x) --> Q(y) electronic relaxation occurs in tens of femtoseconds and the short-time dynamics were first interpreted with account of the time-dependent wave packet theory and Herzberg-Teller contributions.

Excited state structural dynamics and Herzberg-Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation.

Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck-Condon region photodynamics for S(0)-->S(4) electronic state is predominantly along the C(m)-ph stretch while that for S(0)-->S(3) electronic state is predominantly along the porphin ring C(beta)C(beta) stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck-Condon and Herzberg-Teller coupling. Four non-total symmetry vibrational mode upsilon(52,)upsilon(64), upsilon(97) and upsilon(130) in A(2) irreducible representative of TPP were observed in 397.9, 416 and 435.7nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9nm, the A(2) vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7nm.

Excited State Structures and Decay Dynamics of 1,3-Dimethyluracils in Solutions: Resonance Raman and Quantum Mechanical Calculation Study

The resonance Raman spectroscopic study of the excited state structural dynamics of 1,3-dimethyluracil (DMU), 5-bromo-1,3-dimethyluracil (5BrDMU), uracil, and thymine in water and acetonitrile were reported. Density functional theory calculations were carried out to help elucidate the ultraviolet electronic transitions associated with the A-, and B-band absorptions and the vibrational assignments of the resonance Raman spectra. The effect of the methylation at N1, N3 and C5 sites of pyrimidine ring on the structural dynamics of uracils in different solvents were explored on the basis of the resonance Raman intensity patterns. The relative resonance Raman intensities of DMU and 5BrDMU are computed at the B3LYP-TD level. Huge discrepancies between the experimental resonance Raman intensities and the B3LYP-TD predicted ones were observed. The underlying mechanism was briefly discussed. The decay channel through the S1((1)nπ*)/S2((1)ππ*) conical intersection and the S1((1)nπ*)/T1((3)ππ*) intersystem crossing were revealed by using the CASSCF(8,7)/6-31G(d) level of theory calculations.

Corrigendum: Study on the noncoincidence effect phenomenon using matrix isolated Raman spectra and the proposed structural organization model of acetone in condense phase

The isotropic and anisotropic Raman spectra of acetone and deuterated acetone isolated in an argon matrix have been recorded for the understanding of noncoincidence effect (NCE) phenomenon. According to the matrix isolated Raman spectra and DFT calculations, we proposed aggregated model for the explanations of the acetone C=O vibration NCE phenomenon and its concentration effect. The experimental data were in consistence with the DFT calculations performed at the B3LYP-D3/6-311 G (d,p) levels based on the proposed model. The experimental identification of the monomer, dimer and trimer are reported here, and the dynamic of the transformation from monomer to aggregated structure can be easily controlled by tuning annealing temperature.

Solvent-dependent dynamics of hydrogen bonding structure 5-(methylthio)-1, 3, 4-thiadiazole-2(3H)-thione as determined by Raman spectroscopy and theoretical calculation

The vibration spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione (MTTN) in acetonitrile (CH3CN), methanol (CH3OH) and water (H2O) solvents were collected and evaluated via deuterium isotopic substitution Raman spectroscopic experiments. These experiments were combined with the quantum chemical theoretical calculations using the PCM solvent model and normal mode analysis. The results confirmed that the MTTN in CH3CN, CH3OH and H2O have hydrogen bonding (H-bonding) MTTN(solvent)n clusters that produce significantly different Raman intensity patterns in different solvents. Combined with the normal Raman assignment, most resonance Raman spectra were assigned to the vibration modes of the H-bonding MTTN(CH3CN), MTTN(CH3OH)3 and MTTN(H2O)3 clusters in CH3CN, CH3OH and H2O. The theoretically-predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands. The intermolecular>NH⋯O and >NH⋯N H-bonding interactions are key constituents of stable thione structures in MTTN. This underlines the significant structural differences of MTTN in CH3CN, CH3OH and H2O. H-bonding perturbation of MTTN reveal important insights about the intermolecular excited state proton transfer (ESPT) reaction mechanisms in the Franck-Condon region structural dynamics of the thione→thiol tautomer in CH3OH and H2O.

A combined experimental and density functional theory investigation of the hydrogen bonding of 2-cyclohexen-1-one and 3-methyl- 2-cyclohexen-1-one in solvents

Hydrogen bonding is a weak chemical interaction widely existed in the variety of organic and biological molecules. As an important structural motif of pyrimidine bases, the solvent effect of the hydrogen bonding of 2-cyclohexen-1-one (CHO) and 3-methyl- 2-cyclohexen-1-one (3MCHO) and its effect on the frequency shift of the CO stretching mode were investigated by using the FT-Raman and UV absorption spectra and density functional theory calculations. The electronic transitions associated with the UV absorptions in different solvents were calculated at B3LYP-TD/6-31++G(d,p) level of theory and employing SCIPCM solvent model. The vibrational spectra of CHO and 3MCHO were assigned on the basis of the FT-Raman spectra in neat liquid and different solvents, the calculated vibrational spectra of monomer and CHO dimers, and the concentration dependent experiments of the band pair intensities. Hydrogen bonding energies of CHO-(H2O)n (n = 1,2) clusters were predicted. The results reveal that the CHO-(H2O)2 cluster and CHO monomer are respectively the major source of spectral observation in water and cyclohexane, while CHO dimmer and CHO monomer coexist in acetonitrile. The difference in the frequency of the νC=O stretching mode between 3MCHO monomer and CHO monomer in cyclohexane were explored.

Environment-dependent conformation investigation of 3-amino-1,2,4-triazole (3-AT): Raman Spectroscopy and density functional theory

In the paper, diverse tautomers of 3-amino-1,2,4-triazole (3AT) in solid and polar solvent have been explored by FT-IR, FT-Raman and 488nm Raman experiments combing with quantum chemical theoretical calculation using PCM solvent model and normal mode analysis. The vibrational spectra prefer the 3-amino-1,2,4-2H-triazole (2H-3AT) dimer in solid, while in a polar solvent 3AT is apt to the 3-amino-1,2,4-2H-triazole (2H-3AT) monomer. The significant wavenumber difference and Raman intensity patterns in solid and different solvents are induced by hydrogen bond perturbation along >NH⋯N≤ hydrogen bonds on five-membered N-heterocyclic ring. The ground state proton transfer reaction mechanism along the five-membered N-heterocyclic ring is supported by intermolecular hydrogen bonding between 3AT and protonic solvent molecules.

UV and Resonance Raman Spectroscopic and Theoretical Studies on the Solvent-Dependent Ground and Excited-State Thione → Thiol Tautomerization of 4,6-Dimethyl-2-mercaptopyrimidine (DMMP)

The vibrational spectra of 4,6-dimethyl-2-mercaptopyrimidine (DMMP) in acetonitrile, methanol, and water were assigned by resonance Raman spectroscopy through a combination of Fourier-transform infrared spectroscopy (FT-IR), FT-Raman UV-vis spectroscopy, and density functional theoretical (DFT) calculations. The FT-Raman spectra show that the neat solid DMMP is formed as a dimer due to intermolecular hydrogen bonding. In methanol and water, however, the majority of the Raman spectra were assigned to the vibrational modes of DMMP(solvent) n ( n = 1-4) clusters containing NH···O hydrogen bonds. The intermolecular NH···O hydrogen bond interactions, which are key constituents of the stable DMMP thione structure, revealed significant structural differences in acetonitrile, methanol, and water. In addition, UV-induced hydrogen transfer isomeric reactions between the thione and thiol forms of DMMP were detected in water and acetonitrile. DFT calculations indicate that the observed thione → thiol tautomerization should occur easily in lower excited states in acetonitrile and water.

UV–Vis, Fluorescence, and Resonance Raman Spectroscopic and Density Functional Theoretical Studies on 3-Amino-1,2,4-triazole: Microsolvation and Solvent-Dependent Nonadiabatic Excited State Decay in Solution

The microsolvation and photophysics of 3-amino-1,2,4-triazole (3AT) after excitation to the light-absorbing S2(nπ*) state were studied by using resonance Raman spectroscopy and single component artificial force-induced reaction (SC-AFIR) in a global reaction route mapping (GRRM) strategy. The vibrational spectra were assigned on the basis of experimental data and density functional theory (DFT) calculations. The resonance Raman spectra of 3AT were measured to probe the excited state structural dynamics in the Franck-Condon region. The conformations of 3AT(CH3CN)1, 3AT(CH3OH)2, and 3AT(H2O)2 clusters were determined by combining vibrational spectrum experiments and B3LYP/6-311++G(d,p) computations. DFT calculations were carried out to obtain the minimal excitation energies of the lower-lying singlet excited states, and the curve-crossing points. It was revealed that the short-time structural dynamics of 3AT were dominated by the N-N stretching coordinates. An excited state decay mechanism is proposed: 3AT is initially excited to the S2(nπ*) state, then the conical intersection (CI) of the S2(nπ*)/S1(ππ*) potential energy surfaces is crossed, and 3AT then decays to the lower solvent-dependent excited state S1(ππ*). It subsequently returns to the S0 state, accompanied by a large Stokes fluorescence shift, which was interpreted as the stabilized S1(ππ*) excited state bonding to several water molecules via intermolecular hydrogen bonding.