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The electronic structures and photophysical properties of six isomeric Ir(III) complexes with different N -heterocyclic naphthyridine ligands were investigated by density functional theory (DFT) and time dependent DFT (TD-DFT) approach. The radiative transition rates ( k r ) were determined through calculated the spin–orbital coupling (SOC) matrix elements T m H SOC S n and the energy levels ( E Sn and E Tm ). The non-radiative transition rates ( k nr ) were estimated through analysis of the structural distortions, the d -orbital splittings and the energy differences between the S 0 and T 1 states Δ E ( T 1 − S 0 ). As the results, the E Sn , the E Tm and the energy splittings Δ E S 1 - T m and Δ E T m - T m - 1 can be regulated by the position of two nitrogen atoms in naphthyridine ring for studied complexes. Moreover, Ir(III) complex inclusive of quinoxaline heterocyclic ring presents large k r and k nr , so its phosphorescence quantum efficiency is difficult up to be 100%. While two Ir(III) complexes bound to quinazoline heterocyclic ring show weakly emissive because of large k nr . Notably, the presence of the cinnoline heterocyclic ring in the Ir(III) complex makes singlet–triplet intersystem (ISC) rate and k r fast but k nr slow, then leads to its high phosphorescence quantum efficiency. [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: Triazatruxene derivatives and heterofluorenes have drawn increasing attention in the applications of OLED devices due to their particular electronic structures and optical properties. To improve on the thermal and morphological stability and enhance electroluminescent (EL) efficiency, six series of star-shaped triazatruxene/heterofluorene co-polymers have been designed. To reveal structure–property relationships of the novel functional materials, an in-depth theoretical investigation was elaborated using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The results HOMOs, LUMOs, ΔH–L, E g , as well as some other electronic structures and IPs, EAs, λ, τ, the absorption and emission spectra can be tuned by the introduction of heterofluorenes into the triazatruxene core. The various properties of these co-polymers were obtained by extrapolating those of the co-oligomers to infinite chain length. It was concluded that these triazatruxene/heterofluorene co-polymers are interesting optoelectronic functional materials, which have great potential for the application in OLEDs. [Copyright &y& Elsevier]

Abstract: A family of N-heteropentacenes acted as promising candidates for organic semiconductor materials is of immense interest. It should be attributed to the following reasons that (1) the positions, numbers and valence-states of N atom in N-heteropentacenes can effectively tune their electronic structure, stability, solubility, and molecular stacking; (2) diverse intermolecular interaction and π-stacking motifs appear in their crystals. The effect of the position and number of the 6-π-pyrazine on their structures and charge-transport properties has been systematically investigated in our previous work (J. Phys. Chem. C 115 (2011) 21416). Therefore, in this work, the study on the role of 8-π-dihydropyrazine with another valence-state N atoms is our focus. Density functional theory, Marcus electron transfer theory and Brownian diffusion assumption coupled with kinetic Monte-Carlo simulation are applied into this investigation. Our theoretical results indicate that in contrast with pyrazine, dihydropyrazine introduced is more helpful for promoting p-type organic semiconductor materials. For molecule 4, hole mobility of its single crystal theoretically reach 0.71cm2 V−1 s−1, and coupled with its fine hole-injection ability, it should be a promising candidate for p-type organic semiconductor materials. Although the lowest triplet-state energies of the molecules studied are very small, introduction of dihydropyrazine is very helpful for increasing the energies. [Copyright &y& Elsevier]

Abstract: The electronic structures and photophysical properties of phenathroline ligands coordinated to Cu(I), which are substituted in the 2,9-positions with methyl, phenyl, trifluoromethyl and tert-butyl groups, has been studied by density functional theory (DFT) and time-dependent DFT (TDDFT). To investigate the role played by counteranion in these complexes, the highest occupied orbital energies (HOMO), the lowest virtual orbital energies (LUMO), ΔH–L (the energies difference between the HOMO and LUMO), the lowest excitation energies (E S1), ionization potentials (IPs), electron affinities (EAs) and reorganization energies (λ) were computed. And through the study of the geometric relaxations, d-orbital splitting and spin-orbit couplings (SOC) at their optimized S0 and T1 geometries, non-radiative and radiative decay rate constants (k nr and k r) were determined, for comparing and analyzing the different size and push/pull substituents effect on the luminescence quantum yield. Considering these factors, the dtbpdmp complex with tert-butyl group in the 2,9-positions has faster k r and singlet-triplet intersystem crossing (ISC) but slower k nr, which leads to its higher photoluminescent quantum efficiency as compared to the methyl-, phenyl- and trifluoromethyl-based complexes. [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]

Abstract: Exploring the relationship between electronic structure and electroluminescent property has great significance to design some desirable OLED materials. A series of dithienylbenzothiazole derivatives were studied with Density Functional Theory method in this work. The results show that the hole injection/transporting ability of the compound is significantly increased by electron donors (triphenylamine and 9-phenylcarbazole). Introducing the cyano group apparently enhances the electron-injection ability of the compound but reduces its hole-injection ability. The dimethyl-chromene-malononitrile (DCM) group greatly enhances the electron injection/transporting ability of the molecule but has almost no effect on its hole injection/transporting ability. Both the electron reorganization energies and LUMO energy levels of the resulting molecules decrease with increasing electronegativities of the substituents. Extending the π-conjugation length between electron donors and acceptors not only increases the hole/electron injection ability of the molecule, but improves its carrier transport balance. [Copyright &y& Elsevier]

Using thiophene (which has a moderate resonance energy) as a spacer rather than benzene permits better π-electron delocalization and leads to a large nonlinear optical response. Thus, the nonlinear optical coefficients of a series of macrocyclic thiophene derivatives (C[3T_DA] with C symmetry) were studied, and their electronic structures, UV-Vis spectra and static second-order nonlinear optical susceptibilities ( β) were computed. The calculated results showed that Δ E increased and the UV-Vis spectrum redshifted as the number of C[3T_DA] units increased (one C[3T_DA] unit consists of trithiophene and diacetylene). The value of β calculated by either the ZINDO-SOS or the FF method showed the same trend: the absolute value of β increased as the number of units increased. The value of β predicted by ZINDO-SOS was an order of magnitude larger than that predicted by the FF method. However, the results suggest that macrocyclic thiophene compounds potentially exhibit large static second-order nonlinear optical susceptibilities. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The geometrical structure, electronic structure, and one-photon absorption (OPA) properties of a series of magnesium ion (Mg)-selective fluorescent probes based on benzo [h] chromene derivatives have been theoretically studied by using density functional theory (DFT) method and Zerner's intermediate neglect of differential overlap (ZINDO) methods. Their two-photon absorption (TPA) properties are also calculated by using the method of ZINDO/sum-over-states. Results show that all studied probe molecules exhibit large TPA cross-section (δ) in response to Mg in 700- to 1,200-nm range. Furthermore, the δ can be greatly enhanced by introducing acceptor groups to the lateral side of benzo [h] chromene. And that probes with stronger acceptor group show larger δ and result in 70-fold enhancing when coordinate with Mg. Significantly, probe molecules with good cell permeability were also studied by replacing the hydrogen group with acetoxymethyl ester, but δ changed slightly. These results shed light into the design strategy of efficient TP fluorescent probes with large δ and good cell permeability for Mg sensing in living systems. [ABSTRACT FROM AUTHOR]

The optical and electronic properties of spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(4‐t‐butylphenyl)quinoxaline) 1a, spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(4‐methoxyphenyl)quinoxaline) 1b, spiro‐fluorene‐dibenzosuberene[d](1‐(4‐(N,N‐diphenylamino)‐phenyl)‐quinoxaline) 1c, spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methylphenylamino)quinoxaline) 1d, spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methyl‐(4‐methylphenyl)amino)quinoxaline) 1e, spiro‐fluorene‐dibenzosuberene[d](1,4‐bis(methyl‐(4‐methoxyphenyl)amino)quinoxaline) 1f, 5,8‐bis‐(4‐methoxy‐phenyl)‐2,3‐diphenyl‐quinoxaline 1, and N,N,N',N'‐tetraphenyl‐ 5h‐dibenzo[a,d]cycloheptene‐3,7‐diamine 2 were investigated theoretically in this paper. The doubly ortho‐linked quinoxaline/diphenylfluorene hybrids 1a–1f show great potential as bipolar materials for the design of optimized organic light‐emitting diodes (OLEDs). Density functional theory (DFT) and ab initio HF were employed to study the geometric and electronic structures of these molecules in the ground state, and ab initio CIS were used to investigate the lowest singlet excited states. The radiative lifetime (τ) and the maximal absorption/emission wavelength of these molecules were calculated within time‐dependent DFT (TDDFT). The results show that the LUMO energies of the bipolar molecules 1a–1d are all lower than those of 1 and 2, consequently, the electron‐accepting abilities of 1a–1d are greatly improved. The HOMO energies of 1c–1f are all higher than those of 1 and 2, suggesting that the hole‐creating abilities of 1c–1f become better. Also, the results reveal that the HOMO and LUMO energies, energy gaps, IP, EA, as well as the maximal absorption/emission spectra can be tuned feasibly by changing the C5‐ and C8‐substituents in the quinoxaline backbone of these molecules. As expected, these materials show different emission spectra varying from 436.11 to 715.47 nm. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The photophysical properties of organoboron quinolate derivatives can be modified readily by manipulating the coordination environment around the central boron atom. This class of compounds applied in organic light-emitting diodes (OLEDs) materials has been studied by quantum chemistry. To reveal the relationship between the structures and properties of these electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/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 maximum absorption and emission wavelengths of these compounds were calculated using the time-dependent density functional theory method. The solvent effect on the absorption and emission wavelengths of these compounds was also considered by a polarizable continuum model. These results show that boron compounds which containing both the hydroxyquinoline/hydroxybenzoquinoline as ligand and O/S in position X follow the rule, that is, the emission shifts to longer wavelength as covalent nature of the boron-ligand bonding is increased. Meanwhile, the negative HOMO and IPs decrease but the negative LUMO and EAs increase by substitution of O with S in position X. It was deduced that both the hole- and electron-injection abilities are improved by substituting S in place of O in position X. After chemical modification in position R with electron-donating properties of NH or 1,4-diethynyl-2,5-dihexyloxybenzene, introduced 1,4-diethynyl-2,5-dihexyloxybenzene improves both the hole- and electron-transfer rate, which leads to better equilibrium property. It can be concluded that the better equilibrium property depends on the conjugated length of side chain in position R. Moreover, exchanging the substituents R and R in BNO1a and BNO1'a can slightly change the hole-transfer rate by 0.04 eV. According to these calculations, series BNO and BNS can be applied as electron transport and hole transport materials at the same time. Specially, series BNO2 and BNS have better performance than MesB[p-4,4'-biphenyl-NPh(1-naphthyl)] (BNPB) in both the hole- and electron-injection ability. [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]

The geometrical structure, electronic structure, one-photon and two-photon absorption properties of a series of macrocyclic thiophene derivatives C[3T_DA] n (n = 2–5) have been studied using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods theoretically. The results showed that the range of λ (1) maxs is 390–470 nm and λ (2) maxs is 640–670 nm, while, both λ (1) max and λ (2) max gradually enlarge as increasing the number of the C[3T_DA] unit. And C[3T_DA] n compounds exhibited large TPA cross-section ( δ max), and the factors influencing on the δ max values were analyzed in detail. Transition dipole moments M 0k and M kn play important roles on δ max. Both π-electron number (N e) and the product of oscillator strengths from ground state to mediate state (ƒ0k) and from mediate state to final state (ƒkn) are in proportion to δ max. Moreover, δ max linearly depends on the static second-order nonlinear optical susceptibilities ( β 0). [ABSTRACT FROM AUTHOR]

Molecular stacking motifs in solid play a pivotal role on the charge transport properties of materials. The relationship between molecular structure and packing motifs in solid remains challenging. In the present work, the single crystal structures of PEN-O , PEN-N , PEN-CF 3 and TPDO were predicted by evolutionary algorithm using the USPEX program. The stacking motifs, the electronic structures and the stabilities of pentacene ( PEN ) derivatives are systematically investigated by employing density functional theory. Our study expounded how the introduction of heteroatoms (oxygen-atom and nitrogen-atom) and substituent (trifluoromethyl) adjust their electronic structure effectively to improve the capability of carrier injection. Hirshfeld surface analysis was performed for the intermolecular close contact points to rationalize the molecular stacking patterns in solid. In addition, electrostatic potential and energy decomposition by symmetry adapted perturbation theory are analyzed to reveal the effects of heteroatoms and substituents on charge distribution and noncovalent interactions. Through introducing heteroatoms and substituents into PEN , the charge redistribution leads to non-uniform electrostatic potentials of conjugated molecular skeleton, which results in the change of the stacking patterns from herringbone to π-stacking. Furthermore, incorporating oxygen-atom or nitrogen-atom into PEN decreases dispersion energies, while modifying PEN with trifluoromethyl increases the dispersion energy. However, both of them lead to the decrease of the electrostatic and exchange-repulsion energy. The stacking motifs, the electronic structures and the stabilities of pentacene derivatives are systematically investigated and their crystal structures were predicted. Hirshfeld surface analysis and energy decomposition are analyzed to reveal the effects of heteroatoms and substituents on charge distribution and noncovalent interactions. Image 1 • The introduction of O-atom into pentacene can significantly increase the λ e , while incorporating N-atom or –CF 3 group increases it slightly. • O-atom or N-atom separately replaces C-atom in pentacene cannot break C–H⋯π interaction. • Doping O-atom or N-atom reduce E disp , while modifying with –CF 3 increases it, both of which lead to the decrease in E elec and E exch. [ABSTRACT FROM AUTHOR]