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Abstract: Density functional theory (DFT) based calculations on a series of double and single proton-transfer reactions e.g. formamide (FA), acetamide (AA) and trifluoro acetamide (TFA) dimmers are performed to understand the potential energy surfaces during proton transfer processes. Apart from using the N–H distances as proton transfer co-ordinate we have computed the variations in polarizations and chemical hardnesses of the species involved to locate the transition state structures during the double proton transfer reactions. The average polarizability (αav ) and the chemical hardness (η) show their optimum value at the same N–H distance and it corresponds to the transition state for all the three titled complexes. The maximum polarizability and minimum chemical hardness at the transition state (TS) are due to maximal charge separation at TS. We observe that computation of maximum polarizability and minimum chemical hardness along the reaction co-ordinate are the easiest way to locate the transition state during the proton transfer processes. [ABSTRACT FROM AUTHOR]

Potential energy (PE) curves for intramolecular proton transfer in the ground (GSIPT) and intramolecular proton transfer in the excited (ESIPT) states of 3-hydroxychromone (3HC) have been studied using DFT-B3LYP/6-31G(d,p) and TD-DFT/6-31G(d,p) level of theory, respectively. Our calculations suggest the non-viability of GSIPT in 3HC. Excited states PE calculations show the existence of ESIPT process in 3HC. ESIPT in 3HC has also been explained in terms of HOMO and LUMO electron densities of the enol and keto tautomers of 3HC. [ABSTRACT FROM AUTHOR]

Abstract: Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of o-hydroxybenzaldehyde (OHBA) were studied using DFT-B3LYP/6-31G(d) and TD-DFT-B3LYP/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in this compound. Excited states PE calculations support the ESIPT process in OHBA. The contour PE diagram and the variation of oscillator strength along the proton transfer co-ordinate support the dual emission in OHBA. Our calculations also support the experimental observations of Nagaoka et al. [S. Nagaoka, U. Nagashima, N. Ohta, M. Fujita, T. Takemura, J. Phys. Chem. 92 (1988) 166], i.e. normal emission of the title compound comes from S2 state and the red-shifted proton transfer band appears from the state. ESIPT process has also been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of OHBA and from the potential energy surfaces. [Copyright &y& Elsevier]

Abstract: Potential energy surfaces (PES) for the ground and excited state intramolecular proton transfer (ESIPT) processes in 5-hydroxy-flavone (5HF) were studied using DFT-B3LYP/6-31G(d) and TD-DFT/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer (GSIPT) in 5HF. Excited states PES calculations support the existence of ESIPT process in 5HF. ESIPT in 5HF has been explained in terms of HOMO, LUMO electron density of the enol and keto tautomer of 5HF. PES scan by phenyl group rotation suggests that the twisted form, i.e., phenyl group rotated by 18.7° out of benzo-γ-pyrone ring plane is the most stable conformer of 5HF. [Copyright &y& Elsevier]

Abstract: Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 1-hydroxy-2-naphthaldehyde (1H2NA) and 2-hydroxy-3-naphthaldehyde (2H3NA) were studied using DFT/B3LYP(6-31G) and TD-DFT/B3LYP(6-31G) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Excited states PE calculations support the ESIPT process to both 1H2NA and 2H3NA. The wide difference in ESIPT emission process of 1H2NA and 2H3NA have been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of these two compounds. [Copyright &y& Elsevier]