Mechanisms of excited-state intramolecular proton transfer (ESIPT) of 1,2-dihydroxyanthraquinone (ALR) in ethanol solvent and binary solvent of water and ethanol are investigated using the density functional theory and time-dependent density functional theory. The intramolecular hydrogen bond is found to be reinforced in the excited state based on the bond lengths, bond angles, and infrared vibrational spectra of relevant group. The reinforcement of intramolecular hydrogen bond is attributed to the charge transfer in the excited state, which leads the ESIPT to form a keto isomer. The absorption and fluorescence spectra of ALR in binary solvent with different water percentage are obtained and demonstrate the inhibition effect of water on the ESIPT process, which are consistent with the experimentally observation. Furthermore, more water molecules are considered near the carbonyl group and hydroxyl group related to the intramolecular proton transfer to form intermolecular hydrated hydrogen bond with ALR for clarifying the block mechanism of water on ESIPT. The potential energy curves, frontier molecular orbitals, and NBO analysis are calculated for the several complexes in the ground and excited states. The results show that the interrupt role of water on the ESIPT originated from the forming of hydrated hydrogen bond between the carbonyl oxygen atom and the water molecule, which weakens the intramolecular hydrogen bond associated with proton transfer, increases the energy barrier of ESIPT, and thus precludes the transition of ALR-E to ALR-K in the excited state. In addition, the weakening of intramolecular hydrogen bonds is increased as the water molecule number increases. So the inhibitory effect is enhanced by the water quantity, which reasonably explains the experimental attenuating of keto emission spectra as the water percentage in binary solvent increases.
Laser-induced thermal–mechanical damage characteristics of window materials are the focus problems in laser weapon and anti-radiation reinforcement technology. Thermal–mechanical effects and damage characteristics are investigated for cleartran multispectral zinc sulfide ( ZnS ) thin film window materials irradiated by continuous laser using three-dimensional (3D) thermal–mechanical model. Some temperature-dependent parameters are introduced into the model. The temporal-spatial distributions of temperature and thermal stress are exhibited. The damage mechanism is analyzed. The influences of temperature effect of material parameters and laser intensity on the development of thermal stress and the damage characteristics are examined. The results show, the von Mises equivalent stress along the thickness direction is fluctuant, which originates from the transformation of principal stresses from compressive stress to tensile stress with the increase of depth from irradiated surface. The damage originates from the thermal stress but not the melting. The thermal stress is increased and the damage is accelerated by introducing the temperature effect of parameters or the increasing laser intensity.
The absorption and fluorescence spectra have been investigated and assigned by Franck–Condon (FC) simulations at quantum TDDFT level for 4-(3-methoxybenzylidene)-2-methyl-oxazalone (m-MeOBDI) dissolved in neutral, acidic, and basic solvent environments. Four...
The lack of understanding of the
initial decomposition micromechanism
of energetic materials subjected to external stimulation has hindered
its safe storage, usage, and development. The initial thermal decomposition
path of nitrobenzene triggered by molecular thermal motion is investigated
using temperature-dependent anti-Stokes Raman spectra experiments
and first-principles calculations to clarify the initial thermal decomposition
micromechanism. The experiment shows that the symmetric nitro stretching,
antisymmetric nitro stretching, and phenyl ring stretching vibration
modes are active as increasing temperature below 500 K. The DFT method
is used to examine the effects of the three mode vibrations on the
initial decomposition of nitrobenzene by relaxed scan for each relevant
change in bond lengths and bond angles to obtain the optimal reaction
channel leading to initial thermal decomposition of nitrobenzene.
The results demonstrate that the initial thermal decomposition is
the isomerization of nitrobenzene to phenyl nitrite. The optimal reaction
channel leading to the initial isomerization is the increase or decrease
of angle O–N–C from the antisymmetric nitro stretching
vibration, which causes the torsion of nitro group and the subsequent
oxygen atom attacking carbon atom. The scanning energy barrier related
to angle O–N–C is about 62.1 kcal/mol, which is very
consistent with the calculated activation barrier of isomerization
of nitrobenzene. This proves the reliability of our conclusions.
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