Time-dependent Density Functional Theory Level Research Articles

Theoretical study on photophysical properties of angular-shaped mercury(II) bis(acetylide) complexes as light-emitting materials

Abstract An in-depth investigation on the optical and electronic properties of a series of mercury-containing and metal-free arylacetylenes with bridged heteroatoms was provided here. The geometric and electronic structures of the complexes in the ground state are studied with density functional theory and Hartree–Fock, whereas the lowest singlet and triplet excited states are optimized by singles configuration interaction (CIS) methods. At the time-dependent density functional theory (TD-DFT) level, molecular absorptions and emission properties were calculated on the basis of optimized ground- and excited-state geometries, respectively. The calculated lowest-lying absorptions of the investigated complexes are attributed to ligand-to-ligand charge transfer (LLCT), intraligand (IL) and ligand-to-metal charge transfer (LMCT). The results show that the optoelectronic properties for the complexes are affected by the transition-metal atom, various bridge heteroatoms and different end-group substituents. Moreover, the calculated data reveal that the studied molecules have improved charge-transfer rate, especially for designed molecules.

Theoretical Study of the Relations between Structure and Photophysical Properties of Model Oligofluorenes with Central Keto Defect

A systematic study of fluorenone and model oligofluorenes (trimer, pentamer, and heptamer) with a central keto defect was performed at ab initio Hartree-Fock (HF), density functional theory (DFT), configuration interaction singles (CIS), and time-dependent density functional theory (TD-DFT) levels. The main aim of this work was the investigation of the direct influence of the central keto defect on the optimal geometry, torsional potentials, and photophysical properties. From the structural point of view, the optimal all-trans electronic ground state geometries of studied oligomers exhibit a uniform torsion of ca. 44-45 degrees (HF) or 37-38 degrees (DFT). The optical excitation leads to the planarization of the fluorenone and fluorene fragments in the central part of the molecule (approximately 34 degrees for CIS and approximately 29 degrees for TD-DFT). The computed excitation and fluorescence energies show a good agreement with the experiment. These presented theoretical results can be useful in designing novel fluorene-fluorenone optical materials as well as understanding of excitation-relaxation phenomena which may occur in various time-dependent optical experiments.

Multimode simulation of dimer absorption spectra from first principles calculations: Application to the 3,4,9,10-perylenetetracarboxylic diimide dimer

First principles calculations based on density functional theory (DFT) have been combined with the multimode vibronic theory of coupled identical monomers to simulate the absorption spectra of dimers. In comparison to our previous study [J. Guthmuller et al., J. Chem. Theory Comput. 4, 2094 (2008)], where the vibrational excitations strictly accompany the electronic excitations, the vibronic model has been generalized so that the vibronic basis set contains vibrational excitations for both the ground and the excited electronic states. As a matter of illustration, this approach has been applied to a perylenetetracarboxylic diimide dimer employing a fixed dimer geometry. The exciton coupling energy is evaluated with time dependent DFT and random phase approximation calculations and by describing the effects of the solvent with the polarizable continuum model. First, the simulated monomer absorption spectrum is found to be in excellent agreement with experiment. Then, the simulated dimer absorption spectrum presents a strong dependency on the exciton coupling energy and on the inclusion of ground state vibrational excitations in the basis set. It is further shown that considering only fundamental vibrational excitations for the ground electronic state provides almost converged spectra and can therefore be used as a good first approximation. Moreover, the comparison with experiment demonstrates that the dimer absorption spectrum can be successfully reproduced by employing the exciton coupling energy determined at the time dependent DFT level provided that the effects of the solvent are included.

Jones and magnetoelectric birefringence of pure substances — A computational study

We present the first investigation of condensed-phase effects on the Jones (and magnetoelectric) birefringence of a set of nondipolar (CCl4 and CS2) and dipolar (nitro- and chloro-benzene) molecules using a recent implementation of the polarizable continuum model for cubic response functions at the time-dependent density-functional level of theory. The condensed-phase calculations have been performed on the neat liquids of the sample molecules using a nonequilibrium solvation scheme to properly account for the solute–solvent interactions in the presence of a frequency-dependent electromagnetic field. It is demonstrated that the condensed-phase effects as modelled by the polarizable continuum model can be substantial, increasing the observable birefringence by more than sixty percent in the case of CCl4, and by a factor of more than three for CS2. Solvent effects are also substantial for the dipolar molecules, leading to an enhancement by a factor of roughly five for nitrobenzene and by a bit less than 30% for chlorobenzene. Comparison is made with the results of experiment. Our calculated anisotropies confirm that the effect is below current experimental detection limits for CCl4 and CS2. We compute Jones constants of the same order of magnitude as the upper limits given in experiment for nitro- and chlorobenzene.

Quantum Dynamics of the Ultrafast ππ*/nπ* Population Transfer in Uracil and 5-Fluoro-Uracil in Water and Acetonitrile

We present the first fully quantum-mechanical dynamical study of the pi pi* --> n pi* decay in photoexcited uracil derivatives in solution. The dynamics of this process for uracil (U) and 5-fluoro-uracil (5FU) in acetonitrile and aqueous solution is investigated, by treating both electrons and nuclei at the quantum-mechanical level, and solving the time-dependent Schrodinger equation for the evolution of the photoexcited system. The potential energy surfaces along the most relevant nuclear degrees of freedom have been obtained at the time-dependent density functional theory level, accounting for the solvent effect by mixed atomistic/continuum models. The obtained results nicely agree with experimental evidence. For U, we predict an ultrafast (<50 fs) pi pi* --> n pi* decay with 10-25% yields, weakly dependent on the solvent. This finding strongly indicates that the npi* state is responsible for the decay channel observed in experiments for U in polar solvents, yielding to a final recovery of the ground state in tens of picoseconds. At variance, our dynamical calculations predict a remarkable solvent effect for 5FU, showing that the pi pi* --> n pi* decay channel is open in acetonitrile and closed in water, in agreement with the much faster decay observed in experiments in the first solvent. The analysis of our theoretical simulations, also including explicitly the laser excitation step, allows us to point out a number of interesting features for the decay dynamics of photoexcited molecules with close-lying electronic states, whose general interest goes beyond the specific system under investigation.

Magnetically Induced Currents in Bianthraquinodimethane-Stabilized Möbius and Hückel [16]Annulenes

The ring currents, NMR chemical shifts, topology of the chemical bonding, and UV-vis spectra of bianthraquinodimethane-stabilized [16]annulenes possessing Möbius and Hückel topology are investigated. The aromatic character of the title compounds is discussed on the basis of the magnetically induced current density obtained using the gauge-including magnetically induced current (GIMIC) approach. Numerical integration of the current density circling around the [16]annulene ring shows that both the Hückel and the Möbius isomers are non-aromatic. The [16]annulene ring of both isomers sustains a net ring current whose strength is only 0.3 nA/T. The ring current consists of a diamagnetic flow on the outside of the [16]annulene ring and a paramagnetic current inside it. Since the net ring-current strength of the [16]annulene is less than 5% of the ring current strength for benzene, both isomers must be considered non-aromatic by the ring current criterion. The similar bond length alternation of the [16]annulene rings also points to a similarity in aromatic character of the two isomers. The shape of the ring current of the Möbius isomer shows that the current density is somewhat more outspread than that of the Hückel isomer. Spatially separated diatropic and paratropic currents of equal strength follow the annulene bonds. The atoms-in-molecules (AIM) analysis reveals a cage critical point in the region of the outspread current density of the Möbius isomer. Intramolecular CH...pi and pi-pi interactions identified by AIM analysis, in combination with the outspread current density, stabilizes the Möbius isomer relative to the Hückel one. The molecule is characterized by calculating the (13)C and (1)H NMR chemical shifts and the UV-vis spectrum and comparing these to experimental spectra. The (13)C NMR and (1)H NMR chemical shifts are rather similar for the two isomers. The UV-vis spectra are compared with the excitation energies calculated at the time-dependent density functional theory (TDDFT) level using Becke's three-parameter hybrid functional together with the LYP correlation functional (B3LYP), as well as at the approximate coupled cluster singles (CCS) and at the approximate coupled cluster singles and doubles (CC2) levels of theory. The CC2 calculations yield excitation energies in fairly good agreement with experimental data.

Coupled-cluster and density functional theory studies of the electronic excitation spectra of trans-1,3-butadiene and trans-2-propeniminium

The electronic excitation spectra of trans-1,3-butadiene (CH(2)=CH-CH=CH(2)) and trans-2-propeniminium (CH(2)=CH-CH=NH(2)(+)) have been studied at several coupled-cluster and time-dependent density functional theory levels using the linear response approach. Systematic studies employing large correlation-consistent basis sets show that approximate singles and doubles coupled-cluster calculations yield excitation energies in good agreement with experiment for all states except for the two lowest excited A(g) states of trans-1,3-butadiene which have significant multiconfigurational character. Time-dependent density functional theory calculations employing the generalized gradient approximation and hybrid functionals yield too low excitation energies in the basis set limit. In trans-1,3-butadiene, increasing the basis set size by augmenting multiple diffuse functions is observed to reduce the high-lying excitation energies with most density functionals. The decrease in the energies is connected to the incorrect asymptotic behavior of the exchange-correlation potential. The results also demonstrate that standard density functionals are not capable of providing excitation energies of sufficient accuracy for experimental assignments.

Theoretical studies on the spectroscopic properties and the substituent effects of pyridyl triazole Os(II) complexes

To explore the spectroscopic properties of pyridyl triazole Os(II) complexes and how the substituent effects affect the spectroscopic properties of [Os(ptz)2L2] (L=PH3; ptzH=(2-pyridyl)-1,2,4-triazole) (1), [Os(bptz)2L2] (bptzH=3-tert-butyl-5-(2-pyridyl)-1,2,4-triazole) (2), [Os(fptz)2L2] (fptzH=3-(trifluoreomethyl)-5-(2-pyridyl)-1,2,4-triazole) (3), and [Os(fbtz)2L2] (fbtzH=3-(trifluoreomethyl)-5-(4-tert-butyl- 2-pyridyl)-1,2, 4-triazole) (4), the density functional theory (DFT) method at the B3LYP level was used to optimize the geometrical structures in the ground and excited state. The absorption and emission properties of the dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model, the transitions characters of them were assigned. Important correlations between substituent effects and emission spectra and the quantum yield have been obtained by comparing and analyzing the calculated results.

Excitons in potassium bromide: A study using embedded time-dependent density functional theory and equation-of-motion coupled cluster methods

We present a study of the lowest surface and bulk excitations of the well-studied potassium bromide (KBr) system using an embedded cluster method. The excited states of the embedded cluster are studied systematically using time-dependent density functional theory (TDDFT) and high-level equation-of-motion coupled cluster (EOMCC) methods. In particular, we have used EOMCC models with singles and doubles (EOMCCSD) and two approaches which account for the effect of triply excited configurations in non-iterative and iterative fashions. We compare and contrast the results between these theories as well as compare our results with experiment. The bulk–surface exciton shift is also calculated at the TDDFT level and compared with experiment.

Theoretical studies on electronic structures and spectroscopic properties of a series of novel β-diketonate Os(II) complexes

The geometries, electronic structures, and spectroscopic properties of a series of [Os(II)(CO)3(tfa)(acac(X)2)] (tfa = trifluoroacetate; acac = acetoylacetonate; X = H (1), CF3 (2), C6H5 (3), and C10H7 (4)) complexes have been investigated theoretically. The ground and excited state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agreed well with the corresponding experimental results. As indicated in this paper, the highest occupied molecular orbitals were dominantly localized on the Os atom, ctfa (abbv. of CO and tfa), and acac ligand for 1 and 2, acac ligand and X substituent for 3 and 4, while the lowest unoccupied molecular orbitals were mainly composed of acac ligand and X substituent. Under the time-dependent density functional theory (TDDFT) level with the polarized continuum model (PCM), the absorption and phosphorescence in CH2Cl2 media were calculated based on the optimized ground- and excited-state geometries, respectively. The calculated results show that the lowest energy absorptions at 317 (1), 342 (2), 377 (3), and 420 nm (4) are attributed to a change of ππ*/MLCT mixing transition to pure ππ* transition for 1–4, while their phosphorescence emission have similar transition properties. This indicates that the absorption and emission transition characters could be altered by adjusting the π electron-donating ability.

Synthesis, X-ray crystal structure, DFT- and TDDFT-based spectroscopic property investigations on a mixed-ligand chromium(III) complex, bis[2-(2-hydroxyphenyl)benzimidazolato]-(1,10-phenanthroline)chromium(III) isophthalate

A mixed-ligand Cr(III) complex with 2-(2-hydroxyphenyl)benzimidazole, 1,10-phenanthroline and isophthalic acid, [Cr(pbm) 2(phen)]X 0.5 ( 1X 0.5) (Hpbm = 2-(2-hydroxyphenyl)benzimidazole; phen = 1,10-phenanthroline; H 2X = isophthalic acid) has been prepared by heating in aqueous solution and characterized, and the geometric structure and spectroscopic properties, investigated experimentally and theoretically by using the density functional theory level (DFT) and the time-dependent density functional theory level (TDDFT). The theoretical–experimental agreement is satisfactory. Further theoretical analyses of electronic structure and molecular orbitals have demonstrated that the low-lying absorption bands in UV–Vis spectrum are mainly π → π∗ ligand-to-ligand charge transfer transition (LLCT) and or π → ( d z 2 - d x 2 - y 2 - d yz ) ligand-to-metal charge transfer transition (LMCT) in nature.

Synthesis, structure, photoluminescence and theoretical studies of an In(III) complex with 2-(2′-hydroxylphenyl)benzoxazole

The synthesis and characterization of [In(pbx) 3] ( 1) (Hpbx = 2-(2′-hydroxylphenyl)benzoxazole) are presented. The ground and low lying excited electronic states in 1 are studied using density functional theory level (DFT). The optimized geometry is compared to the experimentally observed structure. Time-dependent density functional theory level (TDDFT) is employed to investigate the excited singlet states. The calculated energies of the low lying singlet states in 1 are in considerable agreement with the experimental data. All the low lying transitions are categorized as π → π∗ ligand-to-ligand charge transfer transitions (LLCT) in nature. The emissive state of 1 is assigned as a singlet metal-perturbed π → π∗ ligand-to-ligand charge transfer transition (LLCT).

Mechanism of Ir(ppy)2(N^N)+ (N^N = 2-Phenyl-1H-imidazo[4,5-f][1,10]phenanthroline) Sensor for F−, CF3COOH, and CH3COO−: Density Functional Theory and Time-Dependent Density Functional Theory Studies

The geometries, electronic structures, and spectroscopic properties of Ir(ppy)2(N--N)(+) (1) (N--N = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, ppy = 2-phenylpyridine), Ir(ppy)2(N--N)(+) x F(-) (2), Ir(ppy)2(N--N)(+) x CF3COOH (3/3a), and Ir(ppy)2(N--N)(+) x CH3COO(-) (4) were investigated theoretically. The ground and the excited state geometries of 1-4 were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The optimized geometries agree well with the corresponding experimental results. The HOMOs of 1-4 and 3a are composed of pi(ppy) and d(Ir), and the LUMOs of 1, 2, 3a, and 4 are contributed by pi*(N--N), whereas the LUMO of 3 is composed of pi*(N--N) and pi*(CF3COOH). Under the time-dependent density functional theory level with polarized continuum model model, the absorption and phosphorescence in CH2Cl2 media were calculated on the basis of the optimized ground and excited state geometries, respectively. The lowest-lying absorptions of 1 (412 nm) and 3/3a (409/419 nm) have MLCT/LLCT transition characters, and those of 2 (448 nm) and 4 (427 nm) are contributed by ILCT character. The calculated lowest-energy triplet excited states responsible for phosphorescence of 1 (519 nm) and 3/3a (661/702 nm) have mixing (3)MLCT/(3)LLCT/(3)ILCT characters, but those of 2 and 4 only have (3)ILCT but without (3)MLCT character, which is the reason for the no-emissive character of 2 and 4. Moreover, the phosphorescence character of 3 is hardly changed by different addition sites of CF3COOH group (3a). The calculated results also showed that complex 1 is more suitable for an F(-) sensor than for CF3COOH and CH3COO(-) sensors.

Spin-orbit effects in the photoabsorption of WAu12 and MoAu12: A relativistic time dependent density functional study

The electronic structure of both WAu12 and MoAu12 has been calculated at the density functional theory (DFT) level, employing the zero order regular approximation at the scalar relativistic level and including a spin-orbit coupling. The effect of the inclusion of the spin-orbit coupling is discussed, and the differences assigned to the nature of the encaged atom (W or Mo) are identified. Then, the excitation spectra of both clusters are calculated at the time-dependent DFT level, also in this case at both scalar relativistic and spin-orbit levels. The inclusion of spin-orbit coupling is mandatory for an accurate description in the low energy region. At higher energy, where the density of states is higher, the convoluted intensity can be properly described already at the scalar relativistic level. The consequences of the spin-orbit coupling on the excitation spectrum of the clusters indicate that while in WAu12 the lowest excitations are essentially shifted in energy with respect to the scalar relativistic results, in MoAu12, a dramatic splitting in many lines is actually predicted, revealing a quite different behavior of the two clusters.

Theoretical studies on the structural and optical properties of a series of Os(II) diimine complexes [Os(N ∧N)(CO) 2I 2] (N ∧N = 2,2′-bipyridine(bpy), 4,4′-di- tert-butyl-2,2′-bipyridine(dbubpy), 4,4′-dichlorine-2,2′-bipyridine(dclbpy))

The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(N ∧N)(CO) 2I 2] (N ∧N = 2,2′-bipyridine (bpy) ( 1), 4,4′-di- tert-butyl-2,2′-bipyridine (dbubpy) ( 2), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) ( 3)) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539 nm for 1– 3, respectively, were attributed to the admixture of the [d xy (Os) → π ∗(bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I) → π ∗(bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687 nm also have the 3MLCT/ 3LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H → t-Bu → Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures.

Optimizing organic photovoltaics using tailored heterojunctions: A photoinduced absorption study of oligothiophenes with low band gaps

A power conversion efficiency of 3.4% with an open-circuit voltage of $1\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ was recently demonstrated in a thin film solar cell utilizing fullerene ${\mathrm{C}}_{60}$ as acceptor and a new acceptor-substituted oligothiophene with an optical gap of $1.77\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ as donor [K. Schulze et al., Adv. Mater. (Weinheim, Ger.) 18, 2872 (2006)]. This prompted us to systematically study the energy- and electron transfer processes at the oligothiophene:fullerene heterojunction for a homologous series of these oligothiophenes. Cyclic voltammetry and ultraviolet photoelectron spectroscopy data show that the heterojunction is modified due to tuning of the highest occupied molecular orbital energy for different oligothiophene chain lengths, while the lowest unoccupied molecular orbital energy remains essentially fixed due to the presence of electron-withdrawing end groups (dicyanovinyl) attached to the oligothiophene. Use of photoinduced absorption (PA) allows the study of the electron transfer process at the heterojunction to ${\mathrm{C}}_{60}$. Quantum-chemical calculations performed at the density functional theory and/or time-dependent density functional theory level and cation absorption spectra of diluted $\mathrm{DCV}n\mathrm{T}$ provide an unambiguous identification of the transitions observed in the PA spectra. Upon increasing the effective energy gap of the donor-acceptor pair by increasing the ionization energy of the donor, photoinduced electron transfer is eventually replaced with energy transfer, which alters the photovoltaic operation conditions. The optimum open-circuit voltage of a solar cell is thus a trade-off between efficient charge separation at the interface and maximized effective gap. It appears that the open-circuit voltages of $1.0--1.1\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ in our solar cell devices have reached an optimum since higher voltages result in a loss in charge separation efficiency.

Circular dichroism of helical structures using semiempirical methods

A general semiempirical scheme has been elaborated to simulate circular dichroism (CD) spectra of supramolecular systems. This approach adopts the analytical method of Beck and Hohlneicher [Theor. Chem. Acc. 101, 297 (1999).] to evaluate the one- and two-center integrals over Slater atomic orbitals. The performance of the method, employing INDO/S and CNDO/S semiempirical parametrizations, has been assessed by considering (i) the effect of the size of the singly excited states manifold, (ii) the origin invariance, and (iii) comparisons with the experimental and other theoretical spectra of several helicenes as well as pyridine-pyrimidine oligomers, which can adopt helical conformations. The main results are (i) the INDO/S parametrization with rather small excitation manifolds is able to reproduce, at low computational costs, the experimental CD spectra of several helicenes as well as CD simulations performed at ab initio and time-dependent density functional theory level of approximation; (ii) in the series of homohelicenes, the rotatory strength of the lowest-energy band increases almost linearly with the size of the helix; (iii) as evidenced by the study of tetradodecyloxy helicene bisquinone, packing effects can change the sign of remarkable CD bands, which are used to assign the structure configuration.

Effects of the 3- and 4-Methoxy and Acetamide Substituents and Solvent Environment on the Electronic Properties of N-Substituted 1,8-Naphthalimide Derivatives

The photophysical properties of polar molecules in solution with an intramolecular charge-transfer effect in the excited state depend strongly on the polarity and proticity of the solvents. UV-visible spectra of 1,8-naphthalimide and some N-substituted derivatives in acetic acid, acetonitrile, dichloromethane, and p-dioxane were carried out. Several molecular cluster geometries formed with N-substituted 1,8-naphthalimide derivatives and a large set of random positioning of some solvent molecules in their environment were optimized by a semiempirical method. It provided a complete screening of possible solute-solvent configurations and resulted in a multiple minima hypersurface of the supramolecular systems. With such local minima energies, the main thermodynamic association functions were found. They also provided selected cluster geometries for calculations of vertical electronic transitions with a time-dependent density functional theory (TD-DFT), if the lowest energy structures were considered. Calculated vertical electronic transition energies at the TD-DFT level were compared with experimental data. The experimental absorption UV-visible spectra for the six compounds in the four solvents were performed in our laboratory. Moreover, X-ray photoelectron spectroscospy of the 1,8-naphthalimide was carried out in the ICP-CSIC laboratory. Thermodynamic function values show different association energies between each solvent and the molecules, in correlation with the possibility of hydrogen bond formation and the polarity and dielectric constant of the solvents. The 3- and 4-acetamide 1,8-naphthalimide derivatives have the highest conformer number and the most negative Gibbs free association energy values for a determined solvent. This indicates the importance of the entropic factors.

Theoretical Studies on Structures and Spectroscopic Properties of a Series of Novel Cationic [trans-(C∧N)2Ir(PH3)2]+ (C∧N = ppy, bzq, ppz, dfppy)

The geometries, electronic structures, and spectroscopic properties of a series of novel cationic iridium(III) complexes [trans-(C/N)(2)Ir(PH(3))(2)]+ (C/N = 2-phenylpyridine, 1; benzoquinoline, 2; 1-phenylpytazolato, 3; 2-(4,6-difluorophenyl)pyridimato, 4) were investigated theoretically. The ground- and excited-state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The unoccupied molecular orbitals are dominantly localized on the C/N ligand, while the occupied molecular orbitals are composed of Ir atom and C/N ligand. Under the time-dependent density functional theory (TDDFT) level with the polarized continuum model (PCM) model, the absorption and phosphorescence in acetonitrile (MeCN) media were calculated based on the optimized ground- and excited-state geometries, respectively. The calculated results showed that the lowest-lying absorptions at 364 nm (1), 389 nm (2), 317 nm (3), and 344 nm (4) are all attributed to a {[d(yz)(Ir) + pi(C/N)] --> [pi*(C/N)]} transition with metal-to-ligand and intraligand charge transfer (MLCT/ILCT) characters; moreover, the phosphorescence at 460 (1) and 442 nm (4) originates from the 3{[d(yz)(Ir) + pi(C/N)] [pi*(C/N)]} (3)MLCT/(3)ILCT excited state, while that at 505 (2) and 399 nm (3) can be described as originating from different types of (3)MLCT/(3)ILCT excited state (3){[d(xy)(Ir) + pi(C/N)] [pi*(C/N)]}. The calculated results also revealed that the absorption and emission transition character can be altered by adjusting the pi electron-withdrawing groups and, furthermore, suggested that the phosphorescent color can be tuned by changing the pi-conjugation effect of the C/N ligand.

Synthesis, structure, spectroscopic properties, DFT and TDDFT investigations of copper(II) complex with 2-(2-hydroxyphenyl)benzimidazole

A Cu(II) complex with 2-(2-hydroxyphenyl)benzimidazole [Cu(pbm) 2] ( 1), (Hpbm = 2-(2-hydroxyphenyl)benzimidazole) has been prepared and isolated under hydrothermal condition, and its structural and spectroscopic properties thoroughly investigated. The square-planar geometry was verified by both the density functional theory level (DFT) calculation and X-ray crystallography. A further theoretical analysis of electronic structure of this complex has also been undertaken to gain a deeper insight into the properties of relevant molecular orbitals. The time-dependent density functional theory level (TDDFT) calculation, together with DFT-based molecular orbital analyses, demonstrates that the low-lying absorption bands in UV–vis spectrum are all mainly π → d x 2 – y 2 and/or ( P, σ ) → d x 2 – y 2 ligand-to-metal charge transfer transition (LMCT) in nature.