An Extremely High Molar Extinction Coefficient Ruthenium Sensitizer in Dye-Sensitized Solar Cells: The Effects of pi-Conjugation Extension

We report a heteroleptic ruthenium complex (007) featuring the electron-rich 5-octyl-2,2'-bis(3,4-ethylenedioxythiophene) moiety conjugated with 2,2-bipyridine and exhibiting 10.7% power conversion efficiency measured at the AM1.5G conditions, thanks to the enhanced light-harvesting that is closely related to photocurrent. This C107 sensitizer has an extremely high molar extinction coefficient,of 27.4 x 10(3) M-1 cm(-1) at 559 nm in comparison to its analogue C103 (20.5 x 10(3) M-1 cm(-1) at 550 nm) or Z907 (12.2 x 10(3) M(-1)cm(-1) at 521 nm) with the corresponding 5-hexyl-3,4-ethylenedioxythiopliene- or nonyl-substituted bipyridyl unit. The augmentation of molar extinction coefficients and the bathochromic shift of low-energy absorption peaks along with the pi-conjugation extension are detailed by TD-DFT calculations. The absorptivity of mesoporous titania films grafted with Z907, C103, or C107 sublinearly increases with the molar extinction coefficient of sensitizers, which is consistent with the finding derived from the surface coverage measurements that the packing density of those sensitizers decreases with the geometric enlargement of ancillary ligands.

Formation of Fullerooxazoles from C61HPh3-: The Regioselectivity of Heteroatom Additions

The formation of fullerooxazoles from C61HPh3- has been examined in benzonitrile (PhCN), m-methoxybenzonitrile (m-OCH3PhCN), m-tolunitrile (m-CH3PhCN), and o-tolunitrile (o-CH3PhCN), where cis-1 bisadducts wit h Ph-, m-OCH3Ph-, m-CH3Ph-, and o-CH3Ph-substituted cyclic imidate next to the phenylmethano are formed its evidenced by various characterizations. Interestingly, only regioisomers 2a-d with the oxygen atom bonded to C4/C5 and the nitrogen atom bonded to C3/C6 are generated its demonstrated by heteronuclear multiple bond coherence (HMBC) NMR, while the alternative regioisomers 3a-d, which have the oxygen and nitrogen atoms at C3/C6 and C4/C5, respectively, are not formed from the reactions, even though the DFT (density functional theory) calculations have predicted that the energy differences between the two types of regioisomers are very small, with regioisomers 3a-d actually having lower energies than 2a-d The results are rationalized by the charge distributions Of C61HPh3-, where computational calculations have shown that the negative charges on C4 and C5 are greater than those on C3 and C6, indicating that the exhibited site selectivity of heteroatoms is a result of the charge-directed addition process

Electronic and magnetic properties of the monoclinic phase BiCrO3 from first-principles studies

Based on density functional theory, we systematically studied the electronic and magnetic properties of the real experimental structural phase BiCrO3 with the space group C2/c. It is found that the ground state is a moderately correlated Mott-Hubbard insulator with G-type antiferromagnetic structure, which is in agreement with the experimental observations. The magnetism can be qualitatively understood in terms of the superexchange mechanism via Cr1(t(2g))-O 2p-Cr-2(t(2g)). Moreover, the total energies calculated for various magnetic orderings lead to an estimate of the magnetic interaction constants.

Interaction of H-2 with transition metal homonuclear dimers Cu-2, Ag-2, Au-2 and heteronuclear dimers PdCu, PdAg and PdAu

The reaction mechanisms of the H-2 with the homonuclear dimers M-2 (Cu, Ag, Au) and the heteronuclear dimers PdM (M = Cu, Ag, Au) were studied by use of density functional theory. For the H-2 reactions with homonuclear dimers M-2 (Cu, Ag, Au), it was found that it is easier for Au-2 to dissociate the hydrogen molecule compared with Cu-2 and Ag-2. For H-2 reactions with the heteronuclear dimers PdM (M = Cu, Ag, An), the hydrogen molecule can be easily dissociated at Pd site, rather than at noble metal site.

Charge carrier transporting, photoluminescent, and electroluminescent properties of zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex

Zinc(II)-2-(2-hydroxyphenyl)benzothiazolate complex is an excellent white-light-emitting material. Despite some studies devoted to this complex, no information on the real origin of the unusually broad electroluminescent (EL) emission is available. Therefore, we investigate photoluminescent and EL properties of the zinc complex. Orange phosphorescent emission at 580 nm was observed for the complex in thin film at 77 K, whereas only fluorescent emission was obtained at room temperature. Molecular orbitals, excitation energy, and emission energy of the complex were investigated using quantum chemical calculations. We fabricated the device with a structure of ITO/F16CuPc(5.5 nm)/Zn-complex/Al, where F16CuPc is hexadecafluoro copper phthalocyanine. The EL spectra varied strongly with the thickness of the emissive layer. We observed a significant change in the emission spectra with the viewing angles. Optical interference effects and light emission originating both from fluorescence and from phosphorescence can explain all of the observed phenomena, resulting in the broad light emission for the devices based on the Zn complex. We calculated the charge transfer integral and the reorganization energy to explain why the Zn complex is a better electron transporter than a hole transporter.

Tuning the energy level and photophysical and electroluminescent properties of heavy metal complexes by controlling the ligation of the metal with the carbon of the carbazole unit

Four novel Ir-III and Pt-II complexes with cyclometalated ligands bearing a carbazole framework are prepared and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction studies of complexes 1, 3, and 4 reveal that the 3- or 2-position C atom of the carbazole unit coordinates to the metal center. The difference in the ligation position results in significant shifts in the emission spectra with the changes in wavelength being 84 nm for the Ir complexes and 63 nm for the Pt complexes. The electrochemical behavior and photophysical properties of the complexes are investigated, and correlate well with the results of density functional theory (DFT) calculations. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ(3)/LiF/Al can attain very high efficiencies.

Orbital ordering in Cs2AgF4 from first principles

First-principles calculations using the augmented plane wave plus local orbital method, as implemented in the WIEN2K code, have been used to investigate the structural, electronic, and magnetic properties of the layered perovskite Cs2AgF4. Our calculations indicate that an orthorhombic ground state for Cs2AgF4 is energetically favored over tetragonal. We also find that Cs2AgF4 should be a strong two-dimensional ferromagnet, with very weak antiferromagnetic coupling between the layers, in agreement with the experiment. More importantly, an antiferrodistortive ordering of z(2)-x(2) and z(2)-y(2) orbitals is inferred from the density of states and from a spin density isosurface analysis.

Electronic structures of Al2W, AlW2 clusters and their anions

Possible structures for Al2W and AlW2 clusters and their anions were presented and studied by use of density functional theory B3LYP at various spin multiplicities. The proposed three structures are triangular form with C-2v symmetry; linear structure with D (infinity h) symmetry; and linear structure with C (infinity v) symmetry. The calculated results indicate that structures with C-2v symmetry are the most stable for both neutral clusters and their anions. For Al2W, C-2v Symmetry at spin multiplicity 5 is the ground state, while for its anion, doublet is the lowest. For AlW2 and its anion, doublet and triplet are the ground states, respectively.

Structural stability and electronic state of transition metal trimers

Ground state geometries were searched for transition metal trimers Sc-3, Y-3, La-3, Lu-3, Ti-3, Zr-3, and Hf-3 by density functional methods. For all the studied trimers, our calculation indicates that the ground state geometries are either equilateral triangle (Zr-3 and Hf-3) or near equilateral triangle (Ti-3, Sc-3, Y-3, La-3, and Lu-3). For rare earth trimers Sc-3, Y-3, La-3, and Lu-3, isosceles triangle (near equilateral triangle) at quartet state is the ground state. Isosceles triangle at doublet state is the competitive candidate for the ground state. For Zr-3 and Hf-3, equilateral triangle at singlet state is the most stable. For Ti-3, isosceles triangle (near equilateral triangle) at quintet state gives the ground state. For Sc-3, Zr-3, and Hf-3, where experimental results are available, the predicted geometries are in agreement with experiment in which the ground state is equilateral triangle (Zr-3) or fluxional (Sc-3 and Hf-3). For Y-3, the calculated geometry is in agreement with experimental observation and previous theoretical study that Y-3 is a bent molecule for the ground state.

Combustion. synthesis and luminescence properties of nanocrystalline monoclinic SrAl2O4 : Eu2+

Nanocrystals of SrAl2O4:Eu2+ have been prepared by combustion synthesis. The results of XRD indicated that the resulting SrAl2O4:Eu2+ nanocrystals have a reduced and distorted monoclinic lattice compared with bulk materials. Both the excitation and emission spectra of SrAl2O4:Eu2+ nanocrystals shifts to higher energies in contrast to the bulk materials. The band structure calculation is performed using first-principles full potential-linearized augmented plane wave method within density functional theory. The calculated results are in reasonable agreement with our experimental results.

Novel < 110 >-oriented organic-inorganic perovskite compound stabilized by N-(3-aminopropyl) imidazole with improved optical properties

In the organic-inorganic perovskites family, the < 100 >-oriented type has been extensively investigated as a result of its unique magnetic, optical, and electrical properties, and only one type of < 110 >-oriented hybrid perovskite stabilized by methylammonium and iodoformamidinium cations or the latter themselves has been known so far. In this paper, another novel < 110 >-oriented organic-inorganic perovskite (C6H13N3)-PbBr4 (compound 1) has been prepared by reacting N-(3-aminopropyl)imidazole (API) with PbBr2 in hydrobromic acid. The crystal structure is determined, which indicates that the perovskite is stabilized by API. The introduction of the optically active organic ligand API into the hybrid perovskite results in a red shift and a great enhancement of photoluminescence in the perovskite with respect to organic ligand API itself. These results have been explained according to calculation based on density-functional theory. Moreover, the excellent film processing ability for the perovskite (C6H13N3)PbBr4 together with the improved optical properties makes it have potential application in optoelectronic devices.

Influence of Mn-O-Mn bond angle on the magnetic and electronic properties in YBaMn2O5

The influence of the Mn-O-Mn bond angle on the magnetic and electronic properties of YBaMn2O5 was studied by density functional theory, which was implemented in the CASTEP code. In practical calculation, both G- and A-type antiferromagnetic (AFM) orderings were considered. The calculated results indicated that G-type is more stable than A-type, in agreement with both experiment and previous theoretical study. It is also interesting to note that a transition from G-type to A-type at an Mn-O-Mn angle of ca. 170 degrees was found upon increasing Mn-O-Mn angle. Therefore, the calculation suggested that what is essential to stabilize the G-type AFM state is the reduction of the Mn-O-Mn bond angle. For both magnetic orderings, the compound changes from semiconductor to metal with the increase of Mn-O-Mn angle.

Geometries and electronic properties of Ta-n, TanO and TaOn (n=1-3) clusters

Geometries, vibrational frequencies, electron affinities, ionization potentials and dissociation energies of the title clusters in both neutral and positively and negatively charged states were studied by use of density functional theory. For both neutral and charged species, different initial isomers were studied in order to determine the structure with the lowest energy. Vibrational analysis was also performed in order to characterize these isomers. For Ta-2, Ta-Ta metallic bond is strengthened by adding or removing an electron, i.e. the charged species are much more stable than the neutral counterpart. For Ta-3, equilateral triangle with D-3h symmetry has the lowest energy for both neutral and charged species (near equilateral triangle for cation). TaO and its charged species have much larger dissociation energy compared with other tantalum oxides. For Ta2O and TaO2. structure with C-2v symmetry is much more stable than linear chains. For Ta3O, planar structure with doubly bridging oxygen atoms of C-2v, symmetry is the global minimum for both neutral and charged species. While for TaO3, three-dimensional structures are favored for both neutral (C-1 symmetry) and charged species (C-3v symmetry).

Substitution effect of nitrogen atoms with carbon atoms in porphyrin on the electronic structure and excited states properties

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and the absorption and emission spectra for porphyrin and a series of carbaporphyrins-carbaporphyrin, adj-dicarbaporphyrin, opp-dicarbaporphyrin, tricarbaporphyrin and tetracarbaporphyrin. The ground- and excited-state geometries were optimized at the B3LYP/6-31g(d) and CIS/6-31g(d) level, respectively. The optimized ground-state geometry and absorption spectra of porphyrin, calculated by DFT and time-dependent DFT (TDDFT), are comparable with the available experimental values. Based on the optimized excited-state geometries obtained by CIS/6-31g(d) method, the emission properties are calculated using TDDFT method at the B3LYP/6-31g(d) level. The effects of the substitution of nitrogen atoms with carbon atoms at the center positions of porphyrin are discussed. The results indicate that the two-pyrrole nitrogens are important to the chemical and physical properties for porphyrin.

Geometries and electronic properties of AunPdm (n=1-4, m =-1, 0, 1) clusters

Possible conformers for AunPdm (n = 1-4, m = -1, 0, 1) clusters have been presented and studied by use of density functional theory. The results indicate that for n = 2, linear conformer with C-infinityv symmetry is the most stable for anion species, while for cation and neutral species, conformer with C-2v symmetry is the most stable. For n = 3, 4, conformers with C-2v symmetry (kite-shape) are energetically favored. The calculated electron affinities (EAs) and vertical detachment energies (VDEs) are in good agreement with experiments for n = 1-4. It is also interesting to note that for even n (n = 2, 4), the most stable conformers do not give the best agreement between calculated and experimental EA and VDE values, while for odd n (n = 3), the lowest energy conformer also gives the best agreement. The ionization potentials (IPs) of AunPd clusters are calculated as well.