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In this work, a theoretical study on the detailed vector correlation for the reaction $$\hbox {He}+\hbox {D}_{2}^{+}\rightarrow \hbox {HeD}^{+}+\hbox {D}~(\hbox {v}, \hbox {j})$$ has been carried out at the collision energy of 23.06 kcal/mol with different rotational states of j $$=$$ 0-5 and vibrational states v $$=$$ 1-5 by use of the quasi-classical trajectory calculation on an improved potential energy surface. The features of $${{\varvec{P}}}\mathbf{(}{\varvec{\theta }}_{{\varvec{r}}}{} \mathbf{)}$$ distributions describing k and $$\mathbf{j}^\prime $$ correlations were discussed. In addition, in order to get full knowledge of stereodynamics of the system, the distributions of dihedral angle $${{\varvec{P}}}\mathbf{(}{\varvec{\varphi }}_{{\varvec{r}}}{} \mathbf{)}$$ and the polarization-dependent differential cross-sections (PDDCSs) were also reported. It has been demonstrated that both product alignment and polarization are sensitive to the reagent vibrational and rotational number. Furthermore, the dynamics behavior of the reaction is independently changed with respect to j under a certain v except for the product alignment effect $$({\varvec{P}}({\varvec{\theta }}_{{\varvec{r}}}))$$ , while it exhibits a generally regular trend concerning v when j is invariable. [ABSTRACT FROM AUTHOR]

The 1,8-Dihydroxydibenzo[a,c]phenazine (DHBP) is chosen to investigate the relationship among the extension of π-conjugation framework, excited-state proton transfer and the Stokes shift. The IR spectra, bond and angle analyses show that the two intramolecular hydrogen bonds in DHBP molecule are both significantly strengthened in S1 state. The proton donor methanol molecule can inhibits the hydrogen bond strengthening in S1 state. The increment of π-conjugation framework effectively decreases the Stokes shift and promotes the proton transfer. The potential energy surfaces of DHBP indicate that the reverse double-proton transfer can spontaneously happen in S0 state, and the double proton can easily transfer for its relative low potential energy barrier in S1 state. [ABSTRACT FROM AUTHOR]

In this work, we employed the quasi-classical trajectory (QCT) method to study the vector correlations and the influence of the reagent initial rotational quantum number j for the reaction He + T2+ ( v = 0, j = 0-3) → HeT+ + T on a new potential energy surface (PES). The PES was improved by Aquilanti co-workers (Chem. Phys. Lett. 2009. 469: 26-30). The polarization-dependent differential cross sections (PDDCSs) and the distributions of P( θr), P(r), and P( θr, r) are presented in this work. The plots of the PDDCSs provide us with abundant information about the distribution of the product angular momentum polarization. The P( θr) is used to describe the correlation between k (the relative velocity of the reagent) and j′ (the product rotational angular momentum). The distribution of dihedral angle P(r) shows the k- k′- j′ ( k′ refers to the relative velocity of the product) correlation. The PDDCS calculations illustrate that the product of this reaction is mainly backward scatter and it has the strongest polarization in the backward and sideways scattering directions. At the same time, the results of the P(r) demonstrate that the product HeT+ tends to be oriented along the positive direction of the y axis and it tends to rotate right-handedly in planes parallel to the scattering plane. Moreover, the distribution of the P( θr) manifests that the product angular momentum is aligned along different directions relative to k. The direction of the product alignment may be perpendicular, opposite, or parallel to k. Moreover, our calculations are independent of the initial rotational quantum number. [ABSTRACT FROM AUTHOR]

Abstract: The potential energy curves (PECs) of nine low-lying electronic states (X2Σ+, A2Π, B2Σ+, C2Δ, D2Π, a 4Σ+, 14Δ, b 4Π and 14Σ−) of the CO+ cation have been studied using an ab initio quantum chemical method. The calculations have been performed employing the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV5Z basis set. To improve the quality of the PECs, core–valence correlation and relativistic corrections are included. Relativistic corrections are included using the third-order Douglas–Kroll Hamiltonian approximation. Core–valence correlation corrections are included using a cc-pCVQZ basis set. Relativistic corrections are included at the level of the cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). Analyses show that the effects on the spectroscopic parameters by the core–valence correlation correction, relativistic correction and Davidson modification are obvious, whereas the effect on the spectroscopic parameters by the nonadiabatic correction can be neglected. For the X2Σ+, A2Π, B2Σ+ and C2Δ electronic states, six main isotopologues (12C16O+, 12C17O+, 12C18O+, 13C16O+, 13C17O+ and 13C18O+) have been studied, since their experimental spectroscopic parameters and molecular constants are relatively abundant. For the D2Π, a 4Σ+, 14Δ, 14Σ− and b 4Π electronic states, just the most naturally abundant isotopologue, 12C16O+, is investigated. These results have been compared in detail with those reported in the literature. Excellent agreement has been found between the present results and the experimentally determined ones. The molecular constants of the C2Δ and the spectroscopic parameters of the D2Π, a 4Σ+, 14Δ, 14Σ− and b 4Π electronic states determined by the MRCI+Q/aug-cc-pV5Z+CV+DK calculations are expected to be reliable predicted results. [Copyright &y& Elsevier]

Abstract: The potential energy curves (PECs) of eight low-lying electronic states (X1Σ+, a 3Σ+, b 3Π, d 3Δ, C1Σ−, e 3Σ−, D1Δ and A1Π) of SiS molecule were investigated with the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach with the correlation-consistent basis sets, aug-cc-pV5Z and aug-cc-pV6Z. Effect on the PECs by the relativistic correction is taken into account. The way to consider the relativistic correction is to use the second-order Douglas–Kroll Hamiltonian (DKH2) approximation. And the relativistic correction is made at the level of cc-pV5Z basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). The PECs are extrapolated to the complete basis set (CBS) limit by the two-point total-energy extrapolation scheme. With these PECs, the spectroscopic parameters (Te , De , Re , ωe , ωexe , ωeуe , Be and αe ) are determined and compared with those reported in the literature. With the PECs obtained by the MRCI+Q/DK+56 calculations, the vibrational levels and inertial rotation and centrifugal distortion constants of the first 30 vibrational states are calculated for each electronic state involved here when the rotational quantum number J is equal to zero. Comparison with the measurements shows that the present total-energy extrapolation could improve the quality of spectroscopic parameters. On the whole, as expected, the spectroscopic parameters and molecular constants closest to the experimental data are determined by the MRCI+Q/DK+56 calculations for these electronic states. [Copyright &y& Elsevier]

Abstract: The potential energy curves (PECs) of , A 2 Πu , and D 2 Πg electronic states of ion have been studied using the full valence complete active space self-consistent-field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach together with the aug-cc-pCV5Z basis set within the frozen core approximation for internuclear separations from 0.05 to 1.8nm. And the spectroscopic parameters (Te , Re , ωe , ωexe , Be , αe , D 0 and De ) of three isotopologues (, 14N15N+ and ) have been determined. These parameters have been compared in detail with those of previous study reported in the literature, and excellent agreement has been found between the present results and the experimental data. With these PECs, the complete vibrational states for the , 14N15N+ and isotopologues are computed for the four electronic states. For each electronic state of each non-rotating isotopologue, the vibrational level Gυ , inertial rotation constant Bυ and centrifugal distortion constant Dυ have been reported for the first 30 vibrational states, which agree well with the available experimental data. The ro-vibrational levels have been predicted when the rotational quantum number J is lower than 40 (J ≤39) for these electronic states of species for future experimental or theoretical research. [ABSTRACT FROM AUTHOR]

Abstract: Quasi-classical trajectory (QCT) method is used to calculate the stereodynamics of the reactions H+LiH (v =0, j =0)→H2 +Li and its isotopic variants based on the ground electronic state potential energy surface (PES) reported by Prudente et al. . The reactive probabilities of the title reactions are computed. We also observed the changes of vector correlations and four generalized polarization-dependent differential cross-sections (PDDCSs) at different collision energies, and we compared the stereodynamics among different isotopic variants of the title reactions. The product polarization distribution of the title reactions exhibits distinct difference which may arise from different mass combinations or kinetic energies. [ABSTRACT FROM AUTHOR]

Abstract: Calculations of the dynamics of the reactions O(1 D)+H2 →OH+H, O(1 D)+HD→OH+D, O(1 D)+HD→OD+H and O(1 D)+D2 →OD+D have been performed using the quasi-classical trajectory (QCT) method with symplectic integration. The theoretical calculations were carried out on the ground state 1A′ potential energy surfaces (PES) by Dobbyn and Knowles. The distributions of the dihedral angle P(), the angle between k and j′, P(θr ), and the product vibrational state are presented. The results show that the intermediate geometrical structures and lifetimes of the reactive collisions play a vital role in these reactions. [Copyright &y& Elsevier]

Abstract: The product rotational polarization of the reaction Cl+C3H8→C3H7+HCl is calculated via the quasiclassical trajectory method based on extended London–Eyring–Polanyi–Sato potential energy surface (PES) at collision energies of 6.0, 7.4, and 8.0 kcal/mol. Compared the dynamics of Cl substituting the primary and secondary hydrogen of C3H8, four polarization dependent generalized differential cross-sections (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt) and (2π/σ)(dσ21−/dωt) have been presented in the center of mass frame, respectively. The distribution of dihedral angle p(ϕr), the distribution of angle between k and j′, p(θr), and the angular distribution of product rotational vectors in the form of polar plots in θr and ϕr are calculated as well. The different character of the abstraction of primary vs. secondary hydrogen atoms from C3H8 may be ascribed to that the different PESs and substituent site. The calculated results are in agreement with the experimental data. [Copyright &y& Elsevier]

The intramolecular proton transfer reaction of the 2-amino-3-(2′-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2′-benzothiazolyl)-quinoline (ABT) molecules in both S 0 and S 1 states at B3LYP/6–311 ++G(d,p) level in ethanol solvent have been studied to reveal the deactivation mechanism of the tautomers of the two molecules from the S 1 state to the S 0 state. The results show that the tautomers of ABO and ABT molecules may return to the S 0 state by emitting fluorescence. In addition, the bond lengths, angles and infrared spectra are analyzed to confirm the hydrogen bonds strengthened upon photoexcitation, which can facilitate the proton transfer process. The frontier molecular orbitals (MOs) and natural bond orbital (NBO) are also calculated to indicate the intramolecular charge transfer which can be used to explore the tendency of ESIPT reaction. The potential energy surfaces of the ABO and ABT molecules in the S 0 and S 1 states have been constructed. According to the energy potential barrier of 9.12 kcal/mol for ABO molecule and 5.96 kcal/mol for ABT molecule, it can be indicated that the proton transfer may occur in the S 1 state. [ABSTRACT FROM AUTHOR]

2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol (BBT) is a newly synthesized water-soluble fluorophore dye with two intramolecular hydrogen bonds. It was demonstrated that BBT exhibits the excited-state intramolecular single and double proton transfer emissions in recent experiment. In order to explain the phenomenon, the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) are used to study the ground states and excited states of BBT and its tautomers. The theoretical results confirm that the hydrogen bonds are strengthened upon photoexcitation. To further reveal the proton transfer mechanism, potential energy surfaces of the S 0 and S 1 states have been constructed. According to the energy potential barrier of 13.69 kcal/mol, it was indicated that the double proton transfer may occur in stepwise rather than simultaneously in the S 1 state unless the excited molecule can overcome the barrier. [ABSTRACT FROM AUTHOR]

The entire 23 Λ-S states of the PCl + molecule have been studied by using the high-level relativistic MRCI+Q method with full-electron aug-cc-pCVQZ-DK basis set. The potential energy curves(PECs) and wavefunctions of the states have been calculated. From the PECs, the spectroscopic constants of the bound states are also determined, and the good agreements could be found with the experiments. The high density region of states exhibits many PECs' crossings, which lead to complicated interaction of the states. Here, the interactions arising from the dipolar interaction and spin-orbit coupling (SOC) effect have been discussed in detail. Under the influence of the SOC effect, the A 2 Π state is perturbed by the 1 4 Σ - state. Considering the SOC effect, total 45 Ω states are generated from the original 23 Λ-S states. The transition properties are also predicted, including the transition dipole moments, Franck-Condon factors, and radiative lifetimes. The lifetimes of the transitions A 2 Π 1/2 -X 2 Π 1/2 and A 2 Π 3/2 -X 2 Π 3/2 are determined to be 478.9 ns and 487.0 ns( v' =0), respectively. [ABSTRACT FROM AUTHOR]

Abstract: The potential energy curves (PECs) of the X3Π, a1Σ+, b1Π, A3Σ+, B3Σ−, c1Δ, D3Π, 15Π, 31Σ+, 33Π, 21Π, 23Σ+, 13Δ, 15Σ+, 43Π, 23Σ− and 15Σ− electronic states of the BN molecule are calculated using an ab initio quantum chemical method. The PEC calculations have been made for internuclear separations from 0.06 to 1.20nm using the complete active space self-consistent field (CASSCF) method, which is followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV5Z basis set. To improve the quality of PECs, core-valence correlation and relativistic corrections are included. Relativistic correction calculations are carried out using the third-order Douglas–Kroll Hamiltonian (DKH3) approximation. Core–valence correlation corrections are included using a cc-pCVQZ basis set. Relativistic corrections are calculated at the level of a cc-pVQZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). These PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. The spectroscopic parameters are determined by fitting the vibrational levels, which are calculated in a direct forward manner from the analytic potential by solving the ro-vibrational Schrödinger equation using Numerov''s method. The spectroscopic results have been compared in detail with those reported in the literature. Excellent agreement has been found between the present spectroscopic results and the experimental ones. Using the Breit-Pauli operator, the spin–orbit coupling effect on the spectroscopic parameters is included in the X3Π and D3Π electronic states. The vibrational level, inertial rotation and centrifugal distortion constants are calculated for each vibrational state of each electronic state. And those of the first 20 vibrational states of each electronic state are reported when the rotational quantum number equals zero. Comparison with the measurements shows that the present results are accurate. The spectroscopic parameters of the c1Δ, 15Π, 31Σ+, 33Π, 21Π, 23Σ+, 13Δ, 15Σ+, 43Π and 15Σ− electronic states and the vibrational manifolds of all the electronic states obtained here are expected to be reliable predicted results. [Copyright &y& Elsevier]

Abstract: The ground and three low-lying excited electronic states of the GeO molecule, including Σ+, Σ− and Π symmetry with singlet and triplet spin multiplicities, have been investigated employing the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach. The potential energy curves (PECs) of these states have been calculated with the cc-pV5Z basis set. And the effect on the PECs by the relativistic corrections has been taken into considerations. The way to consider the relativistic corrections is to use the second-order Douglas–Kroll Hamiltonian approximation. For the four electronic states, the spectroscopic parameters (Te , D 0, De , Re , ωe , ωexe , αe and Be ) of 10 isotopes (70Ge16O, 72Ge16O, 73Ge16O, 74Ge16O, 76Ge16O, 70Ge18O, 72Ge18O, 73Ge18O, 74Ge18O, 76Ge18O) have been determined. The spectroscopic parameters have been compared with those of previous investigations reported in the literature, and excellent agreement has been found between the present results and the available data. With the PECs determined here, the first 30 vibrational states for each species are computed for the four electronic states when the rotational quantum number J equals zero (J =0). The vibrational level G(υ), inertial rotation constant Bυ and centrifugal distortion constant Dυ are determined when J =0, which are in excellent agreement with the available experimental data. The ro-vibrational levels have been calculated for these low-lying electronic states of 10 isotopes when J ⩽29. And the transition lines are evaluated according to the transition rule. Comparison with the available experimental observations shows that the present ro-vibrational levels are reliable. [Copyright &y& Elsevier]

Abstract: The potential energy curves of X2Σ+ and A2Πi states of CN radical have been investigated using the complete active space self-consistent-field method followed by the highly accurate valence internally contracted multireference configuration interaction approach in combination with the cc-pV5Z basis set. With the second-order Douglas–Kroll Hamiltonian approximation, the effect on the PECs by the relativistic corrections has been taken into considerations. Employing the cc-pcV5Z basis set, the effect on the spectroscopic parameters by the core-correlate corrections has been evaluated. For the X2Σ+ and A2Πi electronic states, the spectroscopic parameters of these four species (12C14N, 13C14N, 12C15N and 13C15N) have been studied. With the CN potential energy curves obtained here, 43 vibrational states for the X2Σ+ and 60 for the A2Πi states are predicted when the rotational quantum number J is equal to zero (J =0). The vibrational manifolds are determined for the first 40 vibrational states when J =0. And the rovibrational energy levels of four species are calculated until J =29. The results of spectroscopic parameters and molecular constants have been compared in detail with those of the investigations reported in the literature. [ABSTRACT FROM AUTHOR]

Abstract: The equilibrium internuclear separation, harmonic frequency, dissociation energy and potential energy curve (PEC) of the HBr(X1Σ+) molecule have been investigated by using the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with the correlation-consistent quintuple basis set augmented with diffuse functions, aug-cc-pV5Z, in the valence range. The PEC calculations cover the internuclear distance range from 0.08 to 2.08nm. The PEC is fitted to the analytic Murrell–Sorbie function, which is used to reproduce the spectroscopic parameters, such as ωeχe , αe , Be and D 0. The present D 0, De , Re , ωe , ωeχe , αe and Be are of 3.7665eV, 3.9289eV, 0.14195nm, 2642.68cm−1, 45.6118cm−1, 0.23525cm−1 and 8.40417cm−1, respectively, which almost perfectly conform to the available measurements. With the potential determined at the MRCI/aug-cc-pV5Z level of theory, the total of 20 vibrational states is predicted when the rotational quantum number J is set to equal zero (J =0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J =0 for the first time, which are in excellent agreement with the available experimental data. [Copyright &y& Elsevier]

Abstract: The equilibrium internuclear separations, harmonic frequencies and potential energy curves of the AsH(X3Σ − ) radical have been calculated using the coupled-cluster singles–doubles–approximate-triples [CCSD(T)] theory in combination with the series of correlation-consistent basis sets in the valence range. The potential energy curves are all fitted to the Murrell–Sorbie function, which are used to reproduce the spectroscopic parameters such as De , ωeχe , αe , Be and D 0. The present D 0, De , Re , ωe , ωeχe , αe and Be obtained at the cc-pV5Z basis set are of 2.8004eV, 2.9351eV, 0.15137nm, 2194.341cm − 1, 43.1235cm − 1, 0.2031cm − 1 and 7.3980cm − 1, respectively, which almost perfectly conform to the measurements. With the potential obtained at the UCCSD(T)/cc-pV5Z level of theory, a total of 18 vibrational states is predicted when the rotational quantum number J is set to equal zero (J =0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J =0 for the first time, which are in excellent agreement with the experiments. [Copyright &y& Elsevier]

Abstract: The coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory in combination with the series of the correlation-consistent basis sets in the valence range are employed to investigate the internuclear equilibrium separations, harmonic frequencies and potential energy curves (PECs) of the HF+(X2Π) ion. The PECs are all fitted to the Murrell-Sorbie function, which is used to determine the spectroscopic parameters (De , D 0, ωeχe , αe and Be ). By comparison with the available experimental data, the PEC obtained at the basis set, aug-cc-pV5Z, is selected to investigate the vibrational manifolds. The present De , D 0, Re , ωe , ωeχe , αe and Be values, which are attained at the aug-cc-pV5Z basis set, are of 3.6156eV, 3.4262eV, 0.10011nm, 3105.202cm−1, 92.2546cm−1, 0.89146cm−1 and 17.5771cm−1, respectively, which are in excellent agreement with the available experimental results. With the potential obtained at the UCCSD(T)/aug-cc-pV5Z level of theory, a total of 20 vibrational states is predicted when the rotational quantum number J is set to equal zero (J =0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced from the HF+(X2Π) PEC when J =0 for the first time. [Copyright &y& Elsevier]

• The hydrogen bond of 6AI trimer in the excited state were discussed. • The reason of hydrogen bond strength was found that is charges transfer. • We got the detailed proton transfer mechanism for 6AI trimer. • The absorption spectra observed in the experiment has been reclassified. The proton transfer mechanism of 6AI trimer in cyclohexane has been theoretical study by time-dependent density functional theoretical methods. After three 6AI monomers are connected to form trimer by hydrogen bonds, the calculated absorption spectra confirm that the experimental absorption peaks of 6AI monomer (about 280 nm) and 6AI trimer (310 nm) are attributed to the 6AI trimer and TPT tautomer respectively. Through the potential energy curves and the potential energy surface, it can be concluded that the 6AI trimer reaches the TPT tautomer in the S1 state through the concerted mechanism rather than the stepwise mechanism. [ABSTRACT FROM AUTHOR]

• Hydrogen bond O36-H37···N35 of DBTP should be strengthened in S 1 state. • Charge redistribution promotes ESIPT tendency for DBTP. • Ultrafast ESIPT reaction occurs for DBTP due to non-barrier process. We theoretically probe into photo-induced hydrogen bonding effects between S 0 and S 1 states as well as excited state intramolecular proton transfer (ESIPT) behavior for 2,6-bis(benzothiazolyl-2-yl)phenol (DBTP) system. By analyzing primary geometrical parameters involved in hydrogen bond, we confirm O36-H37···N35 of DBTP should be strengthened in the first excited state. By constructing potential energy surfaces for DBTP along with ESITP reactional orientation, we affirm that DBTP molecule undergoes the ultrafast ESIPT process. Once excited to the S 1 state, DBTP quickly transfers its proton forming DBTP-PT tautomer. That is why no fluorescence of DBTP could be reported in experiment. [ABSTRACT FROM AUTHOR]

The excited-state molecular dynamics of 7-hydroxyquinoline-8-carboxylic acid (HCA) were studied to observe its fluorescent properties and proton transfer process. The two intramolecular hydrogen bonds (O-H⋯O and O-H⋯N) of the Enol form were both strengthened after photoexcitation to the first excited (S 1) state. The experimentally observed fluorescence emission (465 nm) was attributed to the theoretical Keto form (470 nm), which implies the occurrence of an excited-state intramolecular double proton transfer (ESIDPT) process. The nonadiabatic dynamics results demonstrate that a single proton transfer from the carboxylic to the nitrogen atom (process-A) occurs in 55 fs, which excludes the ESIDPT concert pathway. The potential energy surface results indicate that process-A (0.08 kcal/mol) induces the occurrence of a second proton transfer from the phenol to the oxygen atom (process-B). Compared to the stepwise ESIDPT reaction that begins with process-B (1.53 kcal/mol), process-A is energy favorable in the S 1 state. Therefore, we propose a reaction path of the following: Enol in the ground state (S 0) → Enol in the S 1 state → proton transferred Keto in the S 1 state (stepwise pathway begins with process-A) → Keto in the S 0 state (fluorescence emission at 470 nm) → Enol in the S 0 state (reversed proton transfer). This process confirms what was predicted by Chou (J. Phys. Chem. Lett. 2011, 2, 3063). Unlabelled Image • The Enol form changes to Keto form through the ESIDPT progress. • The ESIDPT progress significantly affects the fluorescence properties. • The stepwise double proton transfer process is energy favorable in the excited state. [ABSTRACT FROM AUTHOR]