Computational studies on the ground and excited states of BrOOBr

In this work, theoretical computations for the ground and excited states of BrOOBr have been performed at high-level ab initio molecular orbital theories. The ground-state geometries of BrOOBr in different forms (trans, cis, and twist form) have been optimized at the couple-cluster CCSD(T) level of theory with cc-pVTZ and aug-cc-pVTZ basis sets, which indicates that at CCSD(T)/cc-pVTZ level of theory, the twist form is 4.96 kcal/mol more stable than the trans form and 10.67 kcal/mol more stable than the cis form; at the CCSD(T)/aug-cc-pVTZ basis set the twist form is 4.33 kcal/mol more stable than the trans form and 9.54 kcal/mol more stable than the cis form. The vertical excitation energies and potential-energy curves for the singlet and triplet low-lying excited states of BrOOBr were calculated at both the complete active space self-consistent-field (CASSCF) level of theory and the multireference internally contracted configuration interaction (MRCI) level of theory. The differences of potential-energy curves at CASSCF and MRCI levels of theory are found for the BrOOBr excited states. At CASSCF level of theory, none of the BrOOBr excited states are bound. However, at MRCI level of theory, all the BrOOBr states studied in this work are bound or slightly bound at the Frank-Condon region. In addition, the scalar relativistic effect and the spin-orbital coupling effect on the vertical excitation energies of the electronic states of BrOOBr were estimated.     

Calculations of CD and CPL spectra as a tool for evaluation of the conformational differences between ground and excited states of chiral molecules

A method for evaluation of the conformational differences between ground and first excited states of chiral conjugated molecules is suggested. This method is based on comparing calculated and observed CD and CPL spectra.     

Pump-probe spectroscopy of molecules driven by infrared field in both ground and excited electronic states

Pump-probe spectra of molecules driven by strong infrared (IR) field in both ground and excited states are studied theoretically. The role of the final state interaction becomes important when pump and probe pulses overlap, and the Rabi frequency is comparable with the lifetime broadening of the excited state and the duration of the pump pulse. Our theoretical approach is applied to x-ray absorption of nitrogen molecule and valence photoionization of carbon monoxide. It is shown that IR-x-ray pump-probe spectroscopy can directly evidence the delocalization of core hole.     

Zinc ion-tetraphenylporphyrin interactions in the ground and excited states

In the present article, tetraphenylporphyrin a new ratiometric fluorescence sensitizer for zinc ion has been proposed. Electronic absorption, emission and (1)H NMR spectral characteristics of meso-tetraphenylporphyrin (TPP) have been studied in acetonitrile medium in the presence of zinc perchlorate. Absorption spectral studies indicate the formation of a new complex between zinc ion and the porphyrin moiety in the ground state as distinguished from the characteristics of metalo(zinc) porphyrin compound. The energy of maximum fluorescence of porphyrin shifts towards blue with the addition of Zn(ClO(4))(2). Steady state emission studies point to the existence of two emitting species viz, the solvated and the complexed porphyrin in equilibrium. The fluorescence emission of tetraphenylporphyrin at 651-nm bands decreases while that at 605 nm increases upon zinc ion interaction in acetonitrile. Thus, the TPP can behave as a ratiometric fluorescent sensor. This fluorescence modulation of TPP should be applicable to dual-wavelength measurement of various biomolecules or enzyme activities. (1)H NMR spectra of the porphyrin suffered a radical change with the addition of zinc perchlorate which points to the formation of a new porphyrin complex. This change is due to the difference in the electron-donating ability of the pyrrolic nitrogens before and after complexation with Zn(2+). The values of equilibrium constant for the binding process have been determined in acetone and acetonitrile, in both ground and excited states.     

Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory

Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N2, P2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B(e), centrifugal distortion constant D(e), the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E(n)0 were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/-4%), omega(e)(+/-5% mostly without exceeding +/-20%), omega(e)x(e)(+/-5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/-30%), B(e)(+/-8%), D(e)(+/-10%), alpha(e)(+/-10%), and E(n)0(+/-10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e), and alpha(e) in the ground states were given by +/-0.7, +/-10.1, and +/-8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/-0.5, +/-9.2, and +/-9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.     

Order parameters of fluorophores in ground and excited states. Probe molecules in a lyotropic liquid crystal

Perylenc, 9,10-dimethylanthracene and 1,6-diphenyl-1,3,5-hexatriene (DPH) solubilized in a macroscopically aligned lyotropic nematic phase have been studied with linear dichroism (LD), steady-state and time-resolved fluorescence spectroscopy. From LD an order parameter of the fluorophore in its electronic ground state can be obtained, and from time-resolved polarized emission spectroscopy for its excited state. The order parameters of perylene in the ground and excited states are the same within experimental accuracy, but they are significantly different for 9,10-dimethylanthracene and DPH. It is concluded that the orientational distributions of fluorescent probe molecules in ground and excited states are generally not equal. Hence the order parameter of a fluorophore in a microscopically anisotropic and macroscopically isotropic system, e.g. a vesicle suspension, cannot generally be determined directly from the emission anisotropy.     

Dynamics of alkoxy-oligothiophene ground and excited states in nanochannels

Two oligothiophenes, 4,4'-dipentoxy-2,2'-dithiophene and 4,4"-dipentoxy-2,2':5',2":5",2' '-tetrathiophene, have been included in the nanochannels of the autoassembling host TPP (tris-o-phenylenedioxycyclotriphosphazene). The effect of the confinement on the structure and properties of the two dyes, as conformational arrangements, dynamics, and photophysical behavior, was addressed by the combination of high spinning speed solid-state NMR and time-resolved EPR spectroscopy. We compared the conformations of the dyes in their ground and photoexcited triplet states and described in detail the dynamics of the supramolecular adducts from 4 K to room temperature. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains show far slower reorientation motion, being in bulky gauche-rich conformations. These lateral plugs keep the planar core as appended in the space like a nanoscale gyroscope, allowing a reorientation in the motion regime of liquids and a long triplet lifetime at unusually high temperature. The nuclear magnetic properties of the guest dyes are also largely affected by the aromatic rings of the neighboring host, imparting an impressive magnetic susceptibility effect (2 ppm proton shift). The high mobility is due to the formation of a nanocage in a channel where aliphatic and aromatic functions isolate the thiophene moieties. Instead, two conformers of the tetrathiophene twisted on the central bond are stabilized by interaction with the host. They interconvert fast enough to be averaged in the NMR time scale.     

Vibrational relaxation in the excited states of large molecules

Theoretical analysis of the time-dependent triplet-triplet absorption spectrum of anthracene is carried out in terms of the Huang-Rhys spectral function which describes the absorption of molecules thermally equilibrated, due to fast intramolecular processes, at some effective temperature T^*(t) depending on time because of the collisions with the buffer-gas molecules. The close match between the theoretical spectra and the spectra observed by Porter et al. is demonstrated.     

Lithium ion-ketocyanine dye interactions in the ground and excited states

Electronic absorption and emission spectral characteristics of a ketocyanine dye have been studied in solution in the presence of lithium perchlorate. Absorption spectral studies indicate complex formation between lithium ion and the dye in the ground state. The value of the equilibrium constant along with the molar absorbance of the absorbing species has been determined for the dye-cation interaction. The energy of maximum fluorescence shifts toward the red with the addition of LiClO(4). Steady-state emission studies point to the existence of two emitting species, viz., the solvated and the complexed dye in equilibrium. The values of the equilibrium constant for the process have been determined in acetone and acetonitrile. Time-resolved studies in the picosecond domain in pure solvents reveal that the lifetime (tau) value increases as the solvation interaction increases. Time-resolved studies also indicate the presence of two emitting species in equilibrium.     

Fermi and Coulomb holes of molecules in excited states

Correlation holes of electrons with the same (Fermi hole) and different (Coulomb hole) spins in the ground (X¹Σ⁺), first (A¹Σ⁺) and second (B¹II) excited states of LiH were constructed from full configuration interaction (CI ) wave functions. It was found that the shapes of both the Fermi and Coulomb holes in these states are dependent on the location of the reference electron. When the reference electron is chosen to be close to the Li nucleus, the Fermi correlation results in a large negative hole for all three states. However, the A¹Σ⁺ excited state is further characterized by displaying a second hole around the H nucleus, and in the B¹II state, the hole is elongated along the molecular axis. Coulomb correlation shows up strongly in the A¹Σ⁺ state and, in addition, there is clearly correlation of electrons at the two nuclei. These features of the correlation holes were compared with those from a two-Slater-determinant model wave function. The Hartree, Fermi, and Coulomb screening potentials in these states were also studied in the light of possible modeling of the correlation functionals for the excited states. © 1995 John Wiley & Sons, Inc.     

Theoretical studies of conjugation and substituent effect on intramolecular proton transfer in the ground and excited states

The ground- and excited-state intramolecular proton transfer (GSIPT and ESIPT) for 8-hydroxy-4H-naphthalen-1-one (HNA), 5-hydroxynaphthoquinone (HNQ), 1-hydroxy-anthraquione (HAQ), 7-hydroxy-1-indenone (7HIN), 5,8-dihydroxynaphthoquinone (DHNQ) and 4,9-dihydroxyperylene-3,10-quinone (DHP) are studied at B3LYP/6-31G(d,p) and TD B3LYP/6-31G(d,p) level. The calculated results show that the PES of GSIPT for HNA, HNQ and HAQ exhibit a single minimum in the enol zone, while for 7-HIN, DHNQ and DHP exhibit a double minimum and a high barrier between the two minima. The barrierless ESIPT for HNA is predicted, however, the PES of ESIPT for HNQ, HAQ, 7HIN, DHNQ and DHP exhibit a high barrier in the S₁ tautomerism.     

Hydrogen bonding in electronically excited states of molecules

Theoretical Chemistry Accounts - CNDO/2 calculations show that hydrogen bonds in the electronically excited states of +H2O and +HOCH3 systems are slightly weaker than in the ground states. The...     

Rhenium(I) carbonyl complex of 4,7-diphenyl-1,10-phenanthroline-Spectroscopic properties, X-Ray structure, theoretical studies of ground and excited electronic states

The paper presents structural studies of the tricarbonyl complexes incorporating 4,7-diphenyl-1,10-phenanthroline (dpphen) - [Re(CO)₃(dpphen)Cl]₂·Me₂CO (1) and [Re(CO)₃(dpphen)Cl] (2). The absorption and emission spectra of [Re(CO)₃(dpphen)Cl] were discussed with the aid of DFT and time-dependent TD-DFT theories. The theoretical studies reveal mixing between the singlet (S₁) and triplet (T₁) excited states of MLCT character.     

Bonding in the ground state and excited states of copper-alkene complexes

The ground state and ¹B₂ excited state of Cu(C₂H₄)⁺ and of CuX(C₂H₄) (X  F, Cl) have been investigated by the Hartree-Fock-Slater (HFS) method. The main metal-ligand interactions in the ground state are ethene π → Cu 4s donation and Cu 3d_π → ethene π^* backdonation, which have comparable contributions to the metal-ligand bond strength. The excitation of CuX(C₂H₄) does not involve an alkene π → metal charge transfer (LMCT), but instead is metal 3d → alkene π^* charge transfer (MLCT) in character. The implications for the photochemistry of olefin-copper(I) complexes are discussed.     

On the lower excited electronic states of glyoxal

The polarization of both nπ* absorption bands of glyoxal has been measured in a glass matrix of 2-methyltetrahydrofuran by the photoselection method. The second absorption band in the 30 000 cm^?1 region has been assigned to a ¹A_g → ¹B_g nπ* transition. Its intensity is mainly induced by interaction with the solvent. An absorption band at about 43 000 cm^?1 has been ascribed to a charge transfer transition in complexes of glyoxal and 2-MTHF.     

Perturbation theory for excited states of molecules

Components of the electric polarizability tensor are calculated for the three lowest singlet and three lowest triplet excited states of a number of conjugated molecules. The method used is the configuration interaction perturbation theory described in the first two papers of this series. A simpler method based on Hückel theory is examined and found to be unsatisfactory.     

Perturbation theory for excited states of molecules

Components of the electric polarizability tensor are calculated for a number of conjugated hydrocarbons. The methods of calculation used were the configuration interaction perturbation theory and the single configuration perturbation theory introduced in paper 1. The results obtained are compared with experiment and with Hückel calculations. It is found that there is some ambiguity in the experimental evidence. The - separability approximations are discussed and the relationship between Hückel theory and the single configuration method is examined.

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Zusammenfassung Die Komponenten des elektrischen Polarisierbarkeitstensor werden für eine Anzahl konjugierter Moleküle mittels a) einer CI-Störungstheorie und b) einer auf einer einzelnen Konfiguration basierenden Störungstheorie berechnet. Die Resultate werden sowohl mit denen der Hückeltheorie als auch mit dem Experiment verglichen, wobei der letztere Vergleich nicht ganz eindeutig ist. Die -- Separabilität wird diskutiert und die Relation zwischen der Hückeltheorie und der durchgeführten Störungsrechnung untersucht.

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Résumé Les composantes du tenseur de polarisabilité électrique sont calculées pour un certain nombre d'hydrocarbures conjugés. Les méthodes de calcul utilisées ont été celles présentées dans l'article 1: théorie des perturbations multi ou mono configurationnelles. Les résultats obtenus sont comparés à l'expérience et aux calculs par la méthode de Hückel. Une certaine ambiguité se dégage des faits expérimentaux. Les approximations de séparabilité - sont discutées et l'on examine la relation entre la théorie de Hückel et la méthode mono configurationnelle.

     

Vibronic coupling in the ground and excited states of oligoacene cations

The vibrational coupling in the ground and excited states of positively charged naphthalene, anthracene, tetracene, and pentacene molecules is studied on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. Our theoretical and experimental results reveal that, while the main contribution to relaxation energy in the ground state of oligoacene systems comes from high-energy vibrations, the excited-state relaxation energies show a significant redistribution toward lower-frequency vibrations. A direct correlation is found between the nature of the vibronic interaction and the pattern of the electronic state structure.