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Cu(I) complexes have received widespread attention as a promising alternative to traditional noble-metal complexes. Herein, we systematically study the properties of Cu(I) complexes from homo- to hetero-ligands, and found the following: (1) hetero-ligands are beneficial to regulate phosphorescent efficiency; (2) when the hetero-ligands in a tetracoordinated Cu(I) complex are 1:1, the ligands coordinate along the dx2-y2 direction of Cu(I) ion, which can observably suppress structural deformation; (3) unlike the P^P ligand, the N^N ligand can enhance the participation of Cu(I) during the transition process; (4) the addition of an appropriate amount of P^P ligand can effectively raise the energy level of HOMO (highest occupied molecular orbital), enhance the proportion of LLCT (ligand–ligand charge transfer), and thereby increase the available singlet emission transition moments which can be borrowed, thus promoting the radiative decay process. As a result, this work provides a detailed understanding of the effects of different ligands in Cu(I) complexes, and provides a valuable reference and theoretical basis for regulating and designing the phosphorescent properties of Cu(I) complexes in the future. [ABSTRACT FROM AUTHOR]

A theoretical study on a series of neutral heteroleptic Cu(I) complexes with different azole-pyridine-based N^N ligands has been presented to get insight into the effect of various nitrogen atoms in the azole ring on photophysical properties. The results reveal that the highest occupied molecular orbital (HOMO) levels and the emission wavelengths of these complexes are mainly governed by the nitrogen atom number in azole ring. With the increasing number of nitrogen atom, the electron density distribution of HOMO gradually extend from the N^N ligand to the whole molecule, meanwhile, the improved contribution from Cu(d) orbits in HOMO results in an effective mixing of various charge transfermodes, and hence, the fast radiative decay(kr) and the slow non-radiative decay rate(knr) are achieved. The photoluminescence quantum yield (PLQY) show an apparent dependence on the nitrogen atom number in the five-membered nitrogen heterocycles. However, the increasing number of nitrogen atoms is not necessary for increasing PLQY. The complex 3 with 1,2,4-triazole-pyridine-based N^N ligands is considered to be a potential emitter with high phosphorescence efficiency. Finally, we hope that our investigations will contribute to systematical understanding and guiding for material molecular engineering. [ABSTRACT FROM AUTHOR]

Abstract: Transition metal acetylide compounds have attracted enormous attention because of the extraordinary photophysical properties arising from the electronic interaction between the transition metal and the organic molecular fragment. In this study, the geometrical structure, electronic structure, one-photon absorption (OPA) and two-photon absorption (TPA) properties of a series of D–π′–A–π–[Pt]–π–A–π′–D type and A′–π′–A–π–[Pt]–π–A–π′–A′ type platinum(II) acetylides were studied theoretically by using density functional theory (DFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods for getting TPA materials possessing large TPA cross-section. Our analysis suggests that intramolecular charge transfer between center metal and π-conjugated organic fragment dominates in TPA transitions, in which metal center increases conjugation length in the direction of long ligand. This contribution provides detailed theoretical analysis of one- and two-photon absorption property of Platinum (II) acetylide compounds and an effective way for designing of platinum (II)/nickel (II) acetylide compounds possessing large TPA cross-section. [Copyright &y& Elsevier]

Abstract: The geometrical and electronic structures, and one- and two-photon absorption properties of macrocyclic thiophenes possessing push-pull groups were investigated. It shows that λ (1) maxs appear red-shift for the designed macrocycles with strong donor/acceptor (D/A) substituents, and the red-shifts enlarge as increasing the number of D/A pair. As a result, their two-photon absorption cross-section (δ max)s get larger, and the configurations with donor and acceptor location on the opposite site can result in larger δ max, which is ascribed to the enlargement of the stronger intramolecular charge transfer (ICT) between D and A or the inside of the whole ring skeleton. Taking SII series of molecules as an example, the enlargement of the net charge change (ΔQ) is one factor for the increase of δ max. Moreover, transition dipole moments (M 0k and Mkn ) play important roles on the increase of δ max. And the product of oscillator strengths (f 0k × fkn ) is in proportion to δ max. [Copyright &y& Elsevier]

Star-shaped molecules with tailoring functional groups in the core and the arms have great potential application in organic light-emitting devices, because it can be designed to realize low band gap, broad absorption, and excellent solubility for low-cost solution process. To gain an insight into the structure-property relationships, a set of four-arm star-shaped molecules with 2,1,3-benzothiadiazole as the core, different π-conjugated groups as the arm, and triphenylamine or 2-(pyridin-2-yl) pyridine as the end-group were designed. In this study, a systematic investigation into them was carried out using the density functional theory and time-dependent density functional theory methods. The calculated ionization potentials, electron affinities, and reorganization energies (λ) show that the properties of the π-conjugated bridge and the end-group significantly affect the carrier injection and transport characteristics of these molecules, especially for S-BTDP and S-EBTD. Among these molecules, S-BTDP exhibits better electron injection ability due to the introduction of 2-(pyridin-2-yl) pyridine as the end-group. However, S-EBTD, with ethylene as π-conjugated bridge, has excellent hole injection and carrier transport behaviors. We also calculated the singlet-to-triplet exciton-formation cross-section ratio (σ/σ), the exciton-formation fractions (χ), and the absorption and emission spectra of these molecules. We calculated that σ/σ ranges from 1.78 to 2.76 and that χ is ca. 0.37-0.48. These molecules have two absorption bands in the range of 340-410 nm and 500-613 nm, respectively. The calculated emission spectra range from 619 to 706 nm. It can be deduced that the studied 2,1,3-benzothiadiazole-based star-shaped molecules can serve as efficient red light-emitting electroluminescent materials. [ABSTRACT FROM AUTHOR]

The use of triphenyl amino-based derivatives in organic light-emitting diodes (OLEDs) can significantly improve their efficiency and stability and especially their electroluminescence characteristics – most of the new hole-transport materials have this feature. In this study, a series of triphenyl amino-based compounds were computed, including two newly designed molecules. They can function as charge transport materials and emitters with high efficiency and stability. To reveal the relationship between the properties and structures of these bifunctional and multifunctional electroluminescent materials, the ground and excited state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), TD-B3LYP/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials (IPs) and electron affinities (EAs) were computed. The lowest excitation energies, the maximum absorption, and emission wavelengths of these compounds were calculated by employing the time-dependent density functional theory (TD-DFT) method. Also, the mobilities of holes and electrons were studied computationally based on the Marcus electron transfer theory. The CH2Cl2 solvent effect on the absorption spectra of N,N′-di-1-naphthyl-N,N′-diphenylbenzidine (NPB) was considered by polarizable continuum model (PCM). The results obtained for these compounds are in good agreement with the experimental values. These data show that the proposed compounds 1 and 2 (N,B-di-1-naphthyl-N,B-diphenylbenzidine and Mes2N[p-4,4′-biphenyl-NPh(1-naphthyl)]), are multifunctional and bifunctional materials similar to Mes2B[p-4,4′-biphenyl-NPh(1-naphthyl)] (BNPB) and NPB, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The coordination chemistry of polydentate chelating ligands that contain mixed pyridinephenol donor sets has been a sought-after target of study and is a possible extension to the chemistry of polypyridines. In this article, seven compounds, which are the four-coordinate boron complexes containing the mixed phenol-pyridyl group, have been studied by theoretical calculation. They can function as charge transport materials and emitters, with high efficiency and stability. To reveal the relationship between the structures and properties of these bifunctional or 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 (IPs) and electron affinities (EAs) 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, and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory method. As a result of these calculations, the values of HOMO, LUMO, energy gaps, IPs, EAs, and the balance between the hole- and electron-transfer are greatly improved with the substitution of carbazole in compound 6. The calculated emission spectra of the seven studied molecules can almost cover the full UV-vis range (from 447.4 to 649.3 nm). Also, the Stokes shifts are unexpectedly large, ranging from 139.4 to 335.1 nm. This will result in the relatively long fluorescence lifetimes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

As a promising energy storage technology, Li-CO 2 /O 2 batteries not only deliver ultrahigh discharge capacity but also capture and convert CO 2 into renewable energy. The exploration into the deposition and decomposition kinetics of discharge product (Li 2 CO 3) is urgent for the high thermodynamic stability. Herein, the influence of current density on the essential characteristics of Li 2 CO 3 has been explored. The results show that the Li 2 CO 3 with poor crystallinity and elliptical disk morphology can be obtained at medium current density, corresponding to the excellent electrochemical performance including ultrahigh capacity of 5800 mA h/g, lower discharge-charge gap of 1.15 V, and long-term cycle life of 80 cycles. In addition, the morphology and crystallinity of Li 2 CO 3 are tailored by the relative energy barriers for electron migration and O 2 - generation. At a medium current density (500 mA/g), the accelerated electron migration can realize the nucleation rate equivalent to growth one of Li 2 CO 3. At this time, Li 2 CO 3 will uniformly deposit on the cathode surface, forming elliptical disk morphology with poor crystallinity. Obviously, this work provides new sights for promoting the development of Li-CO 2 /O 2 battery through rational design of catalysts to accelerate the deposition and decomposition processes of Li 2 CO 3. [Display omitted] • A systematical study of discharge process and corresponding Li 2 CO 3 characteristics affected by the current density is proposed. • The Li 2 CO 3 characteristics like morphology and crystallinity during the discharge and charge processes are investigated. • The underlying Li 2 CO 3 deposition mechanisms involved with current density are systematically concluded. [ABSTRACT FROM AUTHOR]

Heterocyclic ligands based on 2-pyridyl-azole, have become some of the ideal ligands for metal complexes due to their flexible structure and wide wavelength tunability. In this paper, a series of Cu(N∧N) (P∧P) complexes are studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The results indicate that the combination of incorporation of N atoms and substitution of electron donor-acceptor groups can effectively control the type and the proportion of the lowest triplet states (T 1) phosphorescent transition. A higher matching degree between the effective spin-orbit coupling (SOC) matrix elements and the transition dipole moments (The S n state has both effective SOC and large transition dipole moments of S n →S 0 transition) brings about a larger transition dipole moment M T a of T 1 a→S 0 transition, and further results in the fastest radiative decay rate (k r) for complex 2, although the main transition of which is internal-ligand charge transfer (ILCT). In addition, the non-radiative decay rate (k nr) of complex 2 is lower than other complexes of series 3 (the reorganization energy produced by in-plane bending vibration of C–H bond in six-membered ring is larger than complex 2), so this complex has the highest quantum yield. Overall, the above analyses illustrate that despite the participation of Cu(I) in transition as an indispensable factor for the radiative transition, the higher component ratio does not necessarily lead to a faster k r. In addition, it is also essential to have a well-matched large transition dipole moments of the singlet states S n →S 0 transition involved in the effective SOC. Consequently, in the development of the 2-pyridyl-azole Cu(I) luminescent materials, the high quantum yield materials can be designed by adjusting the substituent at C 3 position and the strength of electron donor-acceptor groups at C 5 position to balance the charge transfer transition modes. Image 1 • The higher component ratio of MLCT does not necessarily lead to a faster radiative decay rate. • With N atoms increasing, the bond C-H in the pyridyl becomes the main source of the reorganization energy. • The transition dipole moments of T 1 a ®S 0 transition plays an important effect on the radiative decay rate. [ABSTRACT FROM AUTHOR]

Abstract: The absorption and emission spectra of six different possible light emitters of coelenteramide: neutral, phenolate anion, phenolate anion with a counter ion (phenolate−–M+), amide anion, pyrazine anion, and the dianion were investigated with the CAM-B3LYP method in the gas phase, in aqueous solution, in a hydrophobic environment and in benzene. The emission spectra of the phenolate anion can be modulated by the covalent character of an oxygen metal bond between the phenolate anion and the countercation. The phenolate anion is more easily formed than the amide anion by deprotonation of the neutral in the excited state. The phenolate anion could not be deprotonated to form the dianion. To examine the charge transfer states of coelenteramide, the charge distributions for the ground and excited states of the complexes were predicted. The emission spectra were predicted in the excited state solvent reaction field. The ground state energies were determined with non-equilibrium solvation, at the excited state geometry with static solvation from the excited state. [Copyright &y& Elsevier]