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The rationality of the minimum electrophilicity principle (MElP) as a companion of minimum polarizability principle and maximum hardness principle is studied for simple diatomic, triatomic, and tetratomic molecules. The applicability is further justified considering organic molecules (e.g., pyrene and acridine yellow) are known for their photophysical properties and accordingly their excited state properties. Single excitation CI (CIS) and time‐dependent density functional theory (TDDFT) are employed to study the excited state reactivity. Two types of excitations, namely vertical and adiabatic, are considered. Processes involving conservation and change in spin multiplicity are included during excitation. The general trend is that the molecules are less electrophilic in the ground state than those in the corresponding excited states. It is found that adiabatic excitation validates the principle even for the triplet ground state molecules undergoing an excitation where spin multiplicity gets altered. The TDDFT method explains the validity of the MElP augmenting the CIS method. This study echoed the MElP during molecular electronic excitation. [ABSTRACT FROM AUTHOR]

The time-dependent density functional theory (TDDFT) method has been performed to investigate the excited state and hydrogen bonding dynamics of a series of photoinduced hydrogen-bonded complexes formed by ( E)- S-(2-aminopropyl) 3-(4-hydroxyphenyl)prop-2-enethioate with water molecules in vacuum. The ground state geometric optimizations and electronic transition energies as well as corresponding oscillator strengths of the low-lying electronic excited states of the ( E)- S-(2-aminopropyl) 3-(4-hydroxyphenyl)prop-2-enethioate monomer and its hydrogen-bonded complexes O1-H2O, O2-H2O, and O1O2-(H2O)2 were calculated by the density functional theory and TDDFT methods, respectively. It is found that in the excited states S1 and S2, the hydrogen bond formed with carbonyl oxygen is strengthened and induces an excitation energy redshift, whereas the hydrogen bond formed with phenolate oxygen is weakened and results in an excitation energy blueshift. This can be confirmed based on the excited state geometric optimizations by the TDDFT method. Furthermore, the frontier molecular orbital analysis reveals that the states with the maximum oscillator strength are mainly contributed by the orbital transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital. These states are of locally excited character, and they correspond to single-bond while the double bond remains unchanged in vacuum. [ABSTRACT FROM AUTHOR]

A better knowledge of the structure of the electronically excited state of substrates is indispensable for the understanding and optimization of . For this study, triplet energies of a variety of α,β-unsaturated γ-lactones (furanones) as well as the structures of the vibrationally relaxed triplet state (T1) have been determined using ab initio coupled-cluster (CCSD) method and/or density functional theory (DFT) calculation. A twist of the original planar structure around C = C bond is found in the relaxed triplet state, π-π*. In the 5-membered ring of furanones the contribution of this mode is limited and the pyramidalization in the C4 position also contributes to the stabilization. The contribution of each stabilization mode is characterized by the dihedral angles and the Mulliken atomic spin densities. The substituent effect on the pyramidalization and the spin density distribution in the C4 and in the C5 position are reported. Depending on the substitution in the C4 position, the orientation of the pyramidalization is either favored syn or anti with respect of the hydroxyl substituent in the C5 position. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

So far, coumarin dyes have been extensively studied with various means to understand their photophysical behaviors and properties. Here, our performing time-dependent density functional theory calculation is aimed at exploring the excited-state hydrogen bonding dynamics of coumarin 153 (C153) in protic ethanol (EtOH) solvent. The calculated results suggest that the excited-state hydrogen bond CO⋯HO between CO group and OH group in the C153-EtOH complex is strengthened, and the S0 → S1 transition of the complex corresponds to the highest occupied molecular orbital (HOMO) hopping to the lowest unoccupied molecular orbital (LUMO). The excited-state hydrogen bond strengthening has been further confirmed by its larger binding energy in the S1 state than in the S0 state. In addition, because of the formation of the hydrogen bond CO⋯HO, a red shift of about 7 nm occurs in the electronic spectra of the C153-EtOH complex, which is in good accordance with the experiment result. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]