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The bonding features and electronic structures of a series of transition metal carbon dioxide complexes have been studied by density functional theory (DFT) calculations combined with natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). NBO analysis shows that the interaction between the metal center and the carbon atom of the carbon dioxide ligand (M–C) is stronger than the other interaction between the metal center and the carbon dioxide ligand. Natural hybrid orbital (NHO) analysis gives the detailed bonding features of the M–C bond for each complex. The NBO charge distribution on the carbon dioxide unit in all studied complexes is negative, which indicates charge transfer from the metal center to the carbon dioxide ligand for all studied complexes. The hyperconjugation effect of the metal center and the two C–O bonds of the carbon dioxide ligand has been estimated using the NBO second-order perturbation stabilization energy. It was found that the NBO second-order stabilization energy of C–O → nM* is sensitive to the coordinated sphere and the metal center. Frontier molecular orbital (FMO) analysis shows that complexes1and4may be good nucleophilic reagents for activation of the carbon dioxide molecule. However, the EDAs show that the M–CO2bond interaction energy of complex4is about two times as large as that of complex1. The high M–CO2bond interaction energy of complex4may limit its practical application. [ABSTRACT FROM PUBLISHER]

In this paper, electronic structures and third-order nonlinear optical (NLO) properties of a series of Pt-Pt bond-containing metal complexes have been calculated by using the density functional theory (DFT) combining with the sum-over-states (SOS) method. In order to check the reliability of this method, the electron correlations and basis sets have been compared. Our calculated results show that introduction of electron donor, thiophene ring and lengthing of organic conjugated ligand can enhance third-order NLO responses. The electronic structure analysis shows that the [Pt-Pt(H2P(CH2)PH2)2] fragment displays strong electron-withdrawing character in these systems. Meanwhile, the third-order NLO response of Pt-Pt bond also has been estimated by using TDDFT-SOS method. An enhancement of third-order NLO response has been observed because of the introduction of the Pt-Pt bond. This is mainly due to the intense and low-lying metal-to-ligand charge transfer (MLCT) and intraligand (IL) CT transitions. [ABSTRACT FROM AUTHOR]

In this article, the nonlinear optical (NLO) switching action of Ru(III/II) carboxylate complexes was investigated by density functional theory (DFT). Among the studied complexed, Ru(III)PhCOO− has the largest β value of 4972 × 10−30 esu. Through the proton transfer (PT) process, the COOH group of Ru(III)PhCOOH and Ru(III)COOH complexes can form the COO− group. Then, COO− group acts as a strong donor and Ru(III) acts as an acceptor, which may be the most favorably used in the development of metal complexes NLO material. The redox NLO switching and PT NLO switching of Ru(III)PhCOO−, Ru(III)PhCOOH, Ru(II)PhCOO−, and Ru(II)PhCOOH complexes have been studied. The β value of Ru(III)PhCOO− complex is ∼36 and ∼48 times larger than those of reduced Ru(II)PhCOO− and Ru(II)PhCOOH, respectively. Note that the β value of deprotonated Ru(III)PhCOO− is ∼215 times larger than that of Ru(III)PhCOOH. The molecular electrostatic potential analysis also confirms that Ru(III)PhCOOH may have poor performance in the second-order NLO response. In addition, the TDDFT calculations show that the ligand to metal charge transfer transition lead to the largest β value of the Ru(III)PhCOO− complex. This investigation provides important insight into the remarkably large NLO properties and NLO switching of Ru(III/II) carboxylate complexes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem 000: 000-000, 2011 [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical (NLO) properties of a series of expanded porphyrins, donor–acceptor-substituted hexaphyrins(1.1.1.1.1.1) and their mono- and bis-Au(III) complexes have been calculated based on density functional theory. The result shows that large-sized hexaphyrin molecules have a large static first hyperpolarizability when compared with the relatively small porphyrin molecule. However, the small porphyrin molecule is intrinsically more efficient for enhancement of the intrinsic NLO response according to intrinsic hyperpolarizability analysis. On the other hand, the switchable NLO properties of aromatic-to-antiaromatic conversion caused by two-electron oxidation/reduction processes have also been probed. The result shows that aromatic→antiaromatic reduction on the hexaphyrin core decreases the static first hyperpolarizability and the intrinsic hyperpolarizability. The value of the aromatic complex is ∼25 times larger than that of the antiaromatic complex. This indicates that the hexaphyrin ring plays an important role in the determination of the second-order NLO response, and the aromatic-to-antiaromatic changes on the hexaphyrin ring cause switchable second-order NLO responses. [ABSTRACT FROM PUBLISHER]

Density functional theory (DFT) was employed to calculate the bonding feature, electron spectrum, and redox properties of a dumbbell-shaped polyoxometalate (POM) cluster, [ [image omitted](PW11O39)2]8-. Our DFT calculations confirm that the quadruple bond interaction between two ReIII centers consists of σ, 2π, and δ orbital overlaps, and the strength of the bonding interactions is in the order σ-bond > π-bond>δ-bond. Time-dependent (TD) DFT calculations suggest that this cluster possesses one strong and four weak absorption bands between 0.7 and 2.5 eV. Excited state calculations show that the Re-Re bond length increases when one electron of the Re-Re bonding δ orbital is shifted to the Re-Re δ* antibonding orbital. Molecular orbital predictions and spin unrestricted calculations indicate that the two Re atoms form the reduced center. The Re-Re bond length increases in one- and two-electron reduction processes because the Re-Re δ* antibonding orbital becomes occupied. However, these changes in the Re-Re bond length in excitation and reduction processes are not substantial because of the weak δ bond. The substitution effect of the central tetrahedron heteroatom of the POM ligand affects the Re-Re bond length, with the Re-Re distance decreasing with the substitution of X from Al to S, Al (2.345 Å) > Si (2.310 Å) > P (2.282 Å) > S (2.257 Å). [ABSTRACT FROM AUTHOR]

Abstract: Time-dependent density functional theory (TDDFT) was employed to study second-order nonlinear optical (NLO) properties of transition metal fullerene complexes with a face to face model. The results show that the ruthenium species possesses the larger second-order NLO response than that of the iron species. Chemical modifications of the fullerene by carbon–carbon bond scission can tune charge transfer character in these complexes, and increase the static first hyperpolarizability. The electronic structure analysis and TDDFT calculations show that the open-cage complex in the ruthenium species possesses low-lying and strong charge transfer transitions, and thus give the largest second-order NLO response. [ABSTRACT FROM AUTHOR]

Abstract: Density function theory (DFT) B3LYP/6-31g(d)-finite field (FF) method was employed to investigate the second-order nonlinear optical (NLO) properties of Nickel(II) polyenyl Schiff base complexes and its polyenyl ligands. It is found that the complexes display higher second-order NLO responses than their ligands. An enhancement of second-order NLO properties of complexes because the Ni2+ ion increased the electron densities distribution of coordinated atoms and adjacent carbon atoms in frontier molecular orbitals, and reduced the gaps between occupied and unoccupied orbitals. Thus the metal complexes display better second-order NLO responses. [Copyright &y& Elsevier]

Abstract: We systematically investigate the linear optical properties and the static second-order nonlinear optical (NLO) properties on a series of two-dimensional (2D) D-π-A-π-D/A-π-D-π-A sandwich metallocarborane-containing molecules with density functional theory (DFT). It can be found that the substitution effect has an influence on the electronic absorption and NLO responses of the 2D molecules. For example, the value is sensitive to the substitution from amino (–NH2) to nitryl (–NO2); the angle between the two A–D branches significantly affects the dipole moment and value. In addition, time-dependent DFT calculations and the analysis of major molecular orbitals predict that the sandwich metallocarborane acts as an electron donor better than electron acceptor. Furthermore, the two strong synchronized charge transfer (CT) coming from the two branches and p–π (B2p–C≡C) conjugation contributes to the second-order polarizabilities in our studied systems. [Copyright &y& Elsevier]

Based on PDCz (1), eight regioisomers (2 – 9) were designed by changing Br substituent position at the carbazole to investigate the structure and property relationship. The calculated results indicate that simply changing the Br substituent position results in significant spin-orbital coupling (SOC) variation. The (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. The other compounds (2 , 4 – 6 , 8 and 9) have significant increase in SOC between singlet and triplet excited states. On the whole, most compounds containing Br substituent has higher SOC than the one that is not substituted. Moreover, the SOC increase is related to the Br substituent positions on the carbazole group. • PDCz and eight regioisomers have been optimized using density functional method. • Change of different Br substituent position lead to a change in T 1 geometries. • The HOMO and LUMO energy levels are mainly influence by the Br substituent position. • Simply change of the Br substituent position results in significant SOC variation. Based on reported PDCz (1), eight isomers (2 – 9) were designed by changing Br substituent positions at the carbazole group to investigate the structure-property relationship by quantum chemistry calculations. The calculated results indicate that an appropriate Br substituent position at the carbazole group is essential for enhancing the spin–orbit coupling (SOC) strength. Among 2 – 9 , The (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. However, other compounds (2 , 4 – 6 , 8 and 9) have significant increase in SOC values between singlet and triplet excited states. Thus, simply changing the Br substituent position would result in significant SOC variation. The systematical investigation on Br substituent position at the carbazole group would provide valuable information for choosing better Br position in experimental synthesis. [ABSTRACT FROM AUTHOR]