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The geometrical structure, electronic structure, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the perylene tetracarboxylic derivatives (PTCDs) were studied theoretically by using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods. The results revealed that increasing the number of naphthalene nucleus, extending the conjugated length on long axis, increasing the strength of donor group on lateral side, decreasing the ΔEH-L (energy gap between the highest occupied orbital and the lowest unoccupied orbital) and keeping the conjugation effect and inductive effect along the same molecular axis are the efficient ways to enlarge TPA cross section of PTCDs compounds. The results that PTCDs compounds exhibited extremely large TPA cross section of around 800–1100 nm (near infrared region) shed light into the significance of the PTCDs compounds for applications in TPA labeling materials in vivo. [ABSTRACT FROM AUTHOR]

The electronic structures and stabilities of cationic MPb12+ clusters (M=B, Al, Ga, In, and Tl) with 50 valence electrons are investigated within density functional theory. It is shown that, at the B3LYP/cc-pVDZ(-PP) and BPW91/cc-pVDZ(-PP) levels of theory, the structures of MPb12+ with icosahedra (Ih) symmetry are energetically favorable, and their high stabilities may arise from the closed-shell nature of the π subsystems which are subject to the 2(Nπ+1)2 rule with Nπ=1. In addition, the possessing of large nucleus-independent chemical shifts of the five kinds of clusters reflects the common aromatic character of these clusters. From the comparison of our studies on the binding energies and the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gaps, the cluster AlPb12+ has higher stability than the others and this is consistent with the recent mass-spectrometric discovery of Al-doped Pbn+ clusters, in which AlPb12+ is highly abundant. The same methods are used to search for the structures of the neutral MPb12 clusters. The calculations reveal that the most stable geometries of the BPb12 and GaPb12 clusters have Ih symmetry, the AlPb12 and InPb12 clusters have Th symmetry, and the TlPb12 cluster has C5v symmetry. Furthermore, the vertical ionization potentials of the neutral MPb12 clusters are smaller than that of some alkali atoms, indicating that the neutral MPb12 clusters possess superalkali character. [ABSTRACT FROM AUTHOR]

The reaction of N (4S) radical with NCO (X2Π) radical has been studied theoretically using density functional theory and ab initio quantum chemistry method. The triplet electronic state [N2CO] potential energy surface (PES) is calculated at the G3B3 and CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(d,p) levels of theory. All the energies of the transition states and isomers in the pathway RP1 are lower than that of the reactants; the rate of this pathway should be very fast. Thus, the novel reaction N + NCO can proceed effectively even at low temperatures and it is expected to play a role in both combustion and interstellar processes. On the basis of the analysis of the kinetics of all pathways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. [ABSTRACT FROM AUTHOR]

A series of regiochemically varied and core size extension-modulated arene- and fluoroarene-thiophene co-oligomers and the unsubstituted sexithiophene α6T were investigated theoretically to explore their electronic and optical properties. These phenylene-thiophene oligomers show great potential for application in organic light-emitting diodes (OLEDs), organic diode lasers, and organic thin-film transistors (OTFTs) because of their feasible tuning of optical and electronic properties by the various structural tunings. Density functional theory (DFT) and the ab initio HF were employed to investigate the geometric and electronic structures of the oligomers in the ground state, and the singles configuration interaction (CIS) methods were used to study the lowest singlet excited state. The lowest excitation energies (Egs), the radiative lifetime τ, and the maximal absorption/emission wavelength of the oligomers were studied within time-dependent DFT (TDDFT). All calculations were performed using the 6-31G(d) basis set. The results show that the HOMOs, LUMOs, energy gaps, ionization potentials (IPs), electron affinities (EAs), and reorganization energies are significantly affected by the various structural tunings in these co-oligomers, which is important for the improvement of the hole and electron injection into OLEDs. Interestingly, the LUMO energy of 1b, 2b, and 3b is lower than that of α6T and 1a, 2a, 3a by about 0.12 ∼ 0.47 eV, indicating that the fluorophenyl-substitution has significantly improved the electron injection properties of the oligomers. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The structures, energetics, spectroscopies and stability of the doublet [Si, C, P, O] radical are explored at the density functional theory and ab initio levels. Eighteen isomers connected by 22 interconversion transition states are located at the DFT/B3LYP/6-311G(d) level. The structures of the kinetically stable isomers and the relevant transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311 + G(2df) single-point energy calculations. At the QCISD/6-311G(d) level, the lowest-lying isomer is the cyclic O-cCSiP 8 (0.0 kcal/mol) with considerable kinetic stability of 22.0 kcal/mol. In addition, two bent isomers OSiCP 1 (7.3 kcal/mol) and SiCPO 3 (34.7 kcal/mol) also possess considerable kinetic stability (more than 10.0 kcal/mol). As a result, three isomers 1, 3 and 8 are predicted to be possible candidates for future experimental and astrophysical detection. The bonding nature of the three isomers is analysed. The calculated results are compared with those of the analogous radical [Si, C, N, O]. Implications in the laboratory and interstellar space are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of [Si, C, P, O] in the laboratory and space. [ABSTRACT FROM AUTHOR]

Calculations with B3LYP within quantum chemical density functional theory have been carried out for 1-H-phosphininium cation and a series of 1-R-phosphininium molecules (R = cyclopentadiene, α and β pyrroles, α and β phosphole, C5BH5&bond; and CH2&bond;). The negative nuclear-independent chemical shift values and the positive aromatic stabilization energies confirm that they are aromatic compounds. In particular, the 1-H-phosphininium cation even exhibits stronger aromatic character than the well-known aromatic phosphinine. The aromatic substituents have strong capability to attract electrons. It is the conjugation and aromaticity that keeps the stability and conformations of the molecules investigated. Owing to the perturbation of the aromatic substituted groups, the predicted large T values and the enlarged HOMO-LUMO gap of the phosphininium cation indicate that these compounds are expected in experiment. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations have been used to study the isomerization process in the NC3P system. At the DFT/B3LYP/6-311G(d) level, 28 triplet and 28 singlet minima were obtained on their respective potential energy surfaces. The linear triplet 3NCCCP is the lowest-energy structure among the isomers. On the triplet PES, only linear isomers 3NCCCP, 3CNCCP, 3CCCNP, and 3CCNCP possess great kinetic and thermodynamic stabilities to exist under low-temperature conditions (such as in the dense interstellar clouds). At the same time, one chain-like and four three-membered-ring isomers on the singlet PES have been located with high kinetic and thermodynamic stabilities. Further CCSD(T)/6-311G(2df)//QCISD/6-311G(d), CCSD(T)/cc-pVTZ//DFT/B3LYP/cc-pVTZ, and CASPT2(14,12)/cc-pVQZ//CASSCF(14,12)/cc-p VQZ calculations are performed on the structures, frequencies, and energies of the relevant species. The bonding natures were analyzed and the results were compared with the analogous NC3N and NC2P molecules so as to aid their future experimental or astrophysical detection. [ABSTRACT FROM AUTHOR]

The structures, energetics, spectroscopies, and stabilities of the doublet [Si, C, N, O] radical are explored at the density functional theory and ab initio levels. Sixteen isomers are located, connected by 29 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest lying isomer is a linear SiNCO 1 (0.0 kcal/mol) mainly featuring a cumulene | · Si = N = C = O. The second and third low-lying isomers are bent OSiCN 2 (8.8) and bent OSiNC 3 (11.1), respectively. All the three low-lying isomers 1, 2, 3, and another high-lying species 5 (75.4) with a linear SiCNO structure are shown to have considerable kinetic stability and may be experimentally observable. The predicted results of isomers 1 and 2 are consistent with the previous mass spectrometry experiments. Moreover, the fourth low-lying species SiOCN 4 (23.9) with bent structure is expected to be observable in low-temperature environments. The bonding nature of the five isomers 1, 2, 3, 4, and 5 is analyzed. The calculated results are compared with those of the analogous molecules C2NO and Si2NO. Implications in interstellar space and N,O-doped SiC vaporization processes are also discussed. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 749–761, 2006 [ABSTRACT FROM AUTHOR]

We report the first attempt to assemble the magic cluster Al4N-on the basis of the density functional theory calculations on a series of -stacked dimers (Al4N-)2, sandwich-like compounds D(Al4N)Mq-(where D Al4N-, Cp-(C5H5-); M Li, Na, K, Be, Mg, Ca) and extended compounds (Cp-)m(Li)n(Al4N-)o(where m, n, and oare integers). For the six metals, the magic Al4N-can only be assembled and grow up in our newly proposed “hetero-decked sandwich” scheme (e.g., CpM(Al4N)q-) so as to avoid cluster fusion. The ground-state hetero-decked sandwich species (Cp-)(M)q(Al4N)-(M Li, Na, K, q1; M Be, Mg, Ca, q2) and the extended sandwich species (Cp-)m(Li)n(Al4N-)oare mainly ionically bonded, cluster-assembled “polyatomic molecules”, grown from the combination of Cp-, M-atoms, and Al4N-. As a prototype for ionic bonding involving intact Al4N-subunits, CpM(Al4N)q-may be a stepping stone toward forming ionic, cluster-assembled AlN compounds. [ABSTRACT FROM AUTHOR]

Ever being a large curiosity, a series of simple "planar tetracoordinate carbon (ptC)" molecules have been recently characterized by experiments. Incorporation of such exotic ptC units into the assembled molecular materials, which will bridge the isolated clusters in molecular beams and the potential solid materials, is very challenging. In this paper, we described the first attempt on how to assemble the fewest-number ptC unit CAl42- into molecular materials in sandwich forms on the basis of the density functional theory calculations on a series of model compounds [D(CAl4)M]q- as well as the saturated compounds [D(CAl4)Mq-] ((D = CAl42-, Cp(C5H5); M = Li, Na, K, Be, Mg, Ca). For M = Li, Be, Mg, and Ca, the ptC unit CAl42- can only be assembled in our newly proposed "heterodecked sandwich" scheme (e.g., [Cp(CAl4)M]q-. (M = Li, Na, K, q = 2; M = Be, Mg, Ca, q = 1)) so as to avoid cluster fusion. For M = Na and K, the ptC unit CAl42- can be assembled in both the traditional "homodecked sandwich" [(CAl4)2M]q- (M = Li, Na, K, q = 3; M = Be, Mg, Ca, q = 2) and the novel heterodecked sandwich schemes. Moreover, the counterions were found to have an important role in determining the type of the ground structures for the homodecked sandwich. Various assembled species in extended frameworks were designed. Notably, among all the designed sandwich species, the ptC unit CAl42- generally prefers to interact with the partner deck at the side (Al-Al bond) or corner (Al atom) site. This has not been reported in the sandwich complexes on the basis of the known decks such as Cp-, P5-, N42-, and Al42-, for which only the traditional face-face interaction type was considered. Our results for the first time showed that the ptC unit CAl42- can act as a new type of "superatom". The present results are expected to enrich the flat carbon chemistry, superatom chemistry, metallocenes, and combinational chemistry. [ABSTRACT FROM AUTHOR]

The photophysics of a series of molecular organic light-emitting diodes (OLEDs) has been studied by theoretical calculation. These molecular OLEDs have been integrated by an electron- and hole-transporting components as well as an emitting components into the donor-π-acceptor (D-π-A) structures: 2-carbazolyl-7-dimesitylboryl-9,9-diethylfluorene (1), trans-4′-N-carbazolyl-4-dimesitylborylstilbene (2), and trans-2-[(4′-N-carbazolyl)styryl]-5-dimesitylborylthiophene (3). To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials and electron affinities were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The lowest excitation energies (Eg) and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory methods. The solvent effect on the emission spectra of these compounds was considered by a polarizable continuum model. As a result of these calculations, it was concluded that the electron injections of these compounds are much easier than Mes2B[p-4,4′-biphenyl-NPh(1-naphthyl)], and the diethylfluorene-based compound has higher electron mobility and better equilibrium properties as compared to the stilbene-based and styrylthiophene-based compounds. [ABSTRACT FROM AUTHOR]

The static first hyperpolarizabilities and origin of nonlinear optical (NLO) properties of [(2-methylnaphthyl)imido]hexamolybdates derivatives have been investigated by density functional theory (DFT). The [(2-methylnaphthyl)imido]hexamolybdate has considerable large first hyperpolarizability, 6.780 × 10 −30esu, and it is larger than that of [(2,6-dimethylphenyl)arylimido]hexamolybdate due to the double aromatic rings in the naphthylimido ligand. The naphthylimido ligand acts as an electron-donor and the polyanion acts as an electron-acceptor. The substituent position on the naphthylimido is a key factor to determine the first hyperpolarizability of (naphthylimido)hexamolybdate derivatives. The derivative, which the iodine atom locates on the para nitrogen on the naphthylimido ligand, has the largest β 0value among the iodine-substituted derivatives. It suggests that the iodine atom is quasi linear with nitrogen and Mo, which is bonded to the nitrogen atom, could generate a large static electronic field and give the large contribution to NLO response. The introducing of electron-donors significantly enhances the first hyperpolarizabilities of (naphthylimido)hexamolybdates comparing with the electron-acceptors as the electron-donating ability is significantly enhanced when the electron-donor is attached to the naphthylimido segment. The present investigation provides important insight into NLO properties of (arylimido)molybdate derivatives. [ABSTRACT FROM AUTHOR]

We predict the assembly and stabilization of the silicon-doped all-metal aromatic unit SiAl3-based on the density functional calculations on a series of model compounds D(SiAl3)Mq-as well as the saturated compounds D(SiAl3)Mn((D SiAl3-, Cp-(C5H5-); M Li, Na, K, Be, Mg, Ca) and the more extended sandwich-like species. For all six metals, SiAl3-can be assembled only in “heterodecked sandwich” scheme (e.g., CpM(SiAl3)q-) so as to avoid cluster fusion. Interestingly, among all the designed sandwich species, SiAl3-generally prefers to interact with the partner deck at the side (Al−Al or Al−Si bonds) or corner (Si or Al atoms) site, in contrast to the known decks such as Cp-, P5-, N42-, and Al42-, which take the traditional face−face interaction type. Such interaction types present an interesting growth pattern that might be applicable to the assembly of Si-doped all-metal aromatic SiAl3-units into highly extended sandwich complexes. Our results for the first time showed that the electronic, structural, and aromatic properties of the silicon-doped all-metal aromatic SiAl3-could be well-retained during cluster assembly. [ABSTRACT FROM AUTHOR]

The electronic structures and stabilities of pure M12-and M122-were systematically investigated within density functional theory. The nucleus-independent chemical shifts (NICSs) of IhSn122-and Pb122-are −5.0 and −20.7 ppm, respectively, based on B3LYP/aug-cc-pVDZ-PP predictions, whereas the NICS of Sn122-is predicted to be 1.1 ppm by B3LYP/LanL2DZ. A startling conclusion is that the NICS4dof Sn122-and NICS5dof Pb122-are −5.0 and −7.5 ppm, respectively, suggesting the significant contribution of the inner d orbitals to the total NICS values. This provides the first quantitative evidence for the existence of “d-orbital aromaticity” in Sn- and Pb-based clusters with three-dimensional structures. The d orbitals also contribute to the total NICSs of the K-coordinated clusters. The NICS predictions suggest that larger basis sets including d-orbitals are needed to analyze the aromaticity of some main-group-metal-based clusters (e.g., Sn- and Pb-based clusters) to obtain accurate predictions. [ABSTRACT FROM AUTHOR]

The radical−radical reaction between the ketenyl radical (HCCO) and nitrogen dioxide (NO2) played a very important role in atmospheric and combustion chemistry. Motivated by recent laboratory characterization about the reaction kinetics of ketenyl radical with nitrogen dioxide, in this contribution, we applied the coupled cluster and density functional theory to explore the mechanism of the title reaction. These calculations indicate that the title reaction proceeds mostly through singlet pathways, less go through triplet pathways. It is found that the HCCO + NO2 reaction initially favors formation of adduct OCCHNO2 (1) with no barrier. Subsequently, starting from isomer 1, the most feasible pathway is ring closure of 1 to isomer O-cCCHN(O)O (2) followed by CO2 extrusion to product HCNO + CO2 (P1), which is the major product with predominant yields. Much less competitively, 1 can take the successive 1,3-H- and 1,3-OH-shift interconversion to isomer OCCNOHO (3a, 3b, 3c) and then to isomer OCOHCNO (4a, 4b), which can finally take a concerted H-shift and C−C bond fission to give HCNO + CO2 (P1). The least competitive pathway is the ring-closure of isomer 3a to form isomer O-cCCN(OH)O (5a, 5b) followed by dissociation to HONC + CO2 (P2) through the direct side CO2 elimination. Because the intermediates and transition states involved in the most favorable channel all lie below the reactants, the title reaction is expected to be rapid, as is confirmed by experiment. Therefore, it can be significant for elimination of nitrogen dioxide pollutants. The present results can lead us to a deep understanding of the mechanism of the title reaction and can be helpful for understanding NOx-combustion chemistry. [ABSTRACT FROM AUTHOR]