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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]

The time-dependent density functional theory (TDDFT) method was performed to investigate the excited-state hydrogen bonding dynamics of 4-amino-1,8-naphthalimide (4ANI) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground-state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated 4ANi and hydrogen-bonded 4ANi-(MeOH)1,4 complexes were calculated by the DFT and TDDFT methods, respectively. We demonstrated that the intermolecular hydrogen bond C═O···H-O and N-H···O-H in the hydrogen-bonded 4ANi-(MeOH)1,4 is strengthened in the electronically excited state, because the electronic excitation energies of the hydrogen-bonded complex are correspondingly decreased compared with that of the isolated 4ANi. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electronically excited state of fluorescent dye in hydrogen-donating solvents exists in many other systems in solution. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]