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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]

The time-dependent density functional theory method was performed to investigate the excited-state hydrogen-bonding dynamics of N-(2-hydroxyethyl)-1,8-naphthalimide (2a) and N-(3-hydroxyethyl)-1,8-naphthalimide (3a) in methanol (meoh) solution. The ground and excited-state geometry optimizations, electronic excitation energies, and corresponding oscillation strengths of the low-lying electronically excited states for the complexes 2a + 2meoh and 3a + 2meoh as well as their monomers 2a and 3a were calculated by density functional theory and time-dependent density functional theory methods, respectively. We demonstrated that the three intermolecular hydrogen bonds of 2a + 2meoh and 3a + 2meoh are strengthened after excitation to the S1 state, and thus induce electronic spectral redshift. Moreover, the electronic excitation energies of the hydrogen-bonded complexes in S1 state are correspondingly decreased compared with those of their corresponding monomer 2a and 3a. In addition, the intramolecular charge transfer of the S1 state for complexes 2a + 2meoh and 3a + 2meoh were theoretically investigated by analysis of molecular orbital. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A series of heteroleptic cyclometalated Ir(III) complexes for organic (OLEDs) application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, the electronic structures, the lowest-lying singlet absorptions and triplet emissions of Ir(dfppy)2(tpip), Ir(tfmppy)2(tpip), and theoretically designed models of Ir(ppy)2(tpip) were investigated with the density functional theory (DFT)-based approaches, where ppy = 2-phenylpyridine, dfppy = 4,6-difluorophenylpyridine, tfmppy = 4-trifluoromethylphenylpyridine, and tpip = tetraphenylimidodiphosphinate. Their structures in the ground and their excited states have been optimized at the DFT/Becke 3-parameter Lee Yang Parr (B3LYP)/Los Alamos National Laboratory 2-double-z (LANL2DZ) and time-dependent DFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy transfer mechanism together with the advantage of low efficiency roll-off for these complexes also can be analyzed here. Copyright © 2013 John Wiley & Sons, Ltd. [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]

In this work, we present the optimized ground state geometrical structures, electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated Tce-CH3COCOOH and Tce-CH3C(OH)2COOH as well as their corresponding hydrogen-bonded dimers Tce-CH3C0C00H-H20 and Tce-CH3C(0H)2C00H-H20 through time-dependent density functional theory method. It is found that the intermo-lecular hydrogen bonds C=0...H-O are strengthened in the electronically excited states of the hydrogen-bonded dimers Tce-CH3C0C00H-H20 and Tce-CH3C(0H)2C00H-H20, in that the excitation energies of the related excited states for the hydrogen-bonded dimers are decreased compared with those of the corresponding monomers. The calculated results are consistent with the rules that are first demonstrated by Zhao on the excited-state hydrogen bonding dynamics. [ABSTRACT FROM AUTHOR]

The photochemistry of pivaloyl, benzoyl, 4-phenylbenzoyl, and 2-anthroyl azides has been studied using femtosecond (fs) time-resolved infrared (TRIR) and UV-vis spectroscopy and interpreted with the aid of computational chemistry. Density functional theory calculations revealed a significant difference in the nature of the lowest singlet excited state for these carbonyl azides. The lowest singlet excited states ( S1) of p-phenylbenzoyl and 2-anthroyl azides are (π,π*) in nature, while the pivaloyl and benzoyl azides S1 states involve ( n,π*) excitations. Nevertheless, for all acyl azides studied here, a similar, and intense, IR band at about 2100 cm−1 has been detected in the ultrafast TRIR experiments following 270 nm excitation. These bands were shifted to lower energy by about 100 cm−1 relative to the N3 stretching mode for the ground states of these azides. These 2100 cm−1 vibrational bands were assigned to the S1 states of acyl azides in agreement with density functional theory calculations. The decay of the acyl azide S1 states was described by bi-exponential functions. The fast component was attributed to the decay of the hot S1 state and the longer component to the decay of the thermally relaxed S1 state. A strong and broad transient absorption in the 350-650 nm spectral range was observed in the fs UV-vis experiments for p-phenylbenzoyl and 2-anthroyl azides. The carrier of this absorption also decayed bi-exponentially, and the time constants were in excellent agreement with those found in the fs TRIR experiments. The slow component of the S1 state decay was found to be dependent on the solvent polarity. When the lifetime of the acyl azide S1 state is substantially longer than the time constant for vibrational cooling of nascent (hot) isocyanate, the correlation between the S1 decay and isocyanate formation was clear. The 270 nm excitation populates the Sn ( n ≥ 2) states of these acyl azides. It was established that a hot nitrene is produced more efficiently from both the Sn and hot S1 states than from the relaxed S1 state of these acyl azides. Thus, time-resolved study provides direct experimental evidence that the S1 state is the precursor of nitrene only when the S1 state is pumped directly and when the S1 state lifetime is longer than the time constant of vibrational cooling of the newborn nitrene. All of these results are consistent with the data obtained recently for 2-napththoyl azide. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Excited state absorption and excited state dynamics of indocyanine‐green (ICG) dissolved in dymethyl sulfoxide were measured using white‐light continuum Z‐scan (WLCZScan) and white‐light continuum pump–probe (WLCPP) techniques. The excited state absorption spectrum, obtained through Z‐scan measurements, revealed saturable absorption (SA) for wavelengths longer than 630 nm, while reverse saturable absorption (RSA) appeared, as indicated by a band at approximately 570 nm. Both processes were modeled by a three‐energy‐level diagram, from which the excited state cross‐section values were determined. SA and RSA were also observed in pump–probe experiments, with a recovery time in the hundreds of picoseconds time scale due to the long lifetime of the first excited state of ICG. Such results contribute to the understanding of ICG optical properties, allowing application in photonics and medicine. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work, some important structures tied closely to the isomerization of 2-(phenylazo)pyridine (2-PAPy) and 4-(phenylazo)pyridine (4-PAPy) on the S0 and S1 states were characterized in detail by using the complete active space SCF (CASSCF) theory. The isomerization mechanism was discussed on the basis of the mapped potential energy surfaces (PESs) and conical intersections (CIs). A comparison of PAPy with azobenzene was carried out to stress the effect of molecular structure on the photoisomerization details. The results indicate that the thermal isomerization for both 2-PAPy and 4-PAPy are mainly attributed to the inversion of CNN angle on the side of the pyridine ring. In view of the energy, an optimized CIrot with a twisting structure supports the rotation mechanism in the photoisomerization of PAPy on the S1 state. However, it was found that another conical intersection (CIinv) with a planar structure is higher in energy than the corresponding trans-FC structure, via which only the PAPy excited on S2 state or vibrationally hot S1 state can relax their excitation energy. Minimum energy paths (MEPs) showed that the relaxation process of cis-PAPy being excited on the S1 state is characterized by a smoothly falling curve, which is very similar to that of azobenzene. Furthermore, a S1 minimum and a transition state (TS1) were found to exist on the MEP starting from the trans-FC point to the CIrot for 4-PAPy, but these two typical structures were not found on the MEP of 2-PAPy. Compared with azobenzene, 4-PAPy exhibits a very similar photoisomerization PES, but a subtly different one can be predicted in the case of 2-PAPy. The present results are expected to provide useful information for the design of photoresponsive materials based on the PAPy units. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (S0) states, the electronic structures of first singlet excited (S1) states are rather delocalized. The electron-donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S0 → S1 absorption energies and S1 → S0 emission energies of 2TV derivatives. The NO2- and NH2-substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro-substituted 2TV exhibit noticeable red shifts as the medium polarity increases. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The electronic properties of the ground state, unrelaxed and relaxed first excited states of push–pull hyperbranched molecules bearing amino and nitro terminal groups have been studied at BB1K/cc-pvdz//HF/6-31g(d), TD-BB1K/cc-pvdz//HF/6-31g(d) and TD-BB1K/cc-pvdz//CIS/6-31g(d) levels of theory, respectively. It was demonstrated that dendritic architecture of push–pull molecules favours the charge transfer in the excited state compared to linear molecules. The possibility of adopting a plane conformation is an important condition for the charge transfer in an excited state. According to the calculations 1:1 ratio of donor and acceptor groups is another important precondition for the manifestation of strong charge separation in the excited state. In case of excess of nitro groups over the amino, some of the excitations participating in the S0 → S1 transition favour the charge transfer in the excited state in the opposite directions, thus decreasing the charge separation. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]