State Electronic Configuration Research Articles

Aroylhydrazone‐based nickel(II) complexes: Synthesis and their structural, density functional theory (DFT), biological and catalytic studies

Nickel(II) complexes of tridentate NNO donor aroylhydrazones, viz., di‐2‐pyridyl ketone‐4‐methoxybenzhydrazone monohydrate (DKMBH·H2O) and 2‐acetylpyrazine‐4‐methoxybenzhydrazone monohydrate (APMBH·H2O), were synthesized and characterized using various methods, including spectral techniques (Fourier transform infrared [FT‐IR], UV–vis) and analytical methods (elemental and X‐ray diffraction [XRD] analysis). Single‐crystal XRD was used to elucidate the crystal structures of nickel(II) complexes 1 and 2. The XRD analysis revealed that the respective ligands coordinated to the Ni(II) center through the deprotonated iminolate form in complex 1 and the neutral amido form in complex 2, resulting in distorted octahedral geometries. The ground state electronic configurations of the complexes were studied using the B3LYP/UB3LYP levels of DFT. Using absorption spectral titration methods, the interactions of complexes with CT‐DNA and bovine serum albumin (BSA) protein were examined. The observed data demonstrate that the complexes adopt an intercalative binding mode to bind to CT‐DNA and BSA protein. Additionally, the antioxidant activity of the nickel(II) complexes and their ligands was determined using 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH). Complex 2 demonstrated the highest radical scavenging activity of the compounds studied (IC50 = 3.81 mM). Furthermore, molecular docking studies were performed to understand how the complexes can interact with the SARS‐CoV‐2 main protease. The results revealed that complex 2 had the highest docking score (−8.18 kcal/mol) when compared with the other complexes under study. Aside from their biological properties, the nickel complexes heterogenized on functionalized SBA‐15 showed promising catalytic activity, achieving 98% yield in the reduction of nitrobenzene, forming exclusively aniline as the end product.

Localized electronic reconfiguration at CoNi-BTC-MOFs to accelerate oxygen evolution reaction

To efficiently control oxygen evolution reaction (OER) at electrocatalysts holds enormous promise for large-scale production of clean energy, but faces the scarcity of practical regulation strategies due to underexplored catalytic mechanism. Herein, a facile and feasible strategy is developed involving metal-metal super-exchange interaction to manipulate the electronic state configuration of catalysts, and the as-synthesized Ni-doped Co-1,3,5-benzenetricarboxylic acid Metal-Organic Frameworks (MOFs) only require an overpotential as low as 260 mV to reach a large current of 200 mA cm−2, which is much lower than 400 mV for the commercial RuO2 catalyst. The introduced Ni atoms lead to more broadly occupied states and d-band center close to the Fermi energy level for the spin-polarization of the electrons in Co atoms, thus decreasing the orbital occupancy to facilitate the adsorption/desorption of the reaction intermediates and lowering the rate-determining step barrier to accelerate OER. Our findings have an important paradigm role in the design of electrocatalysts with high performance for oxygen evolution reaction.

Study of electronic structure and optical transition properties of low-lying excited states of AuB molecules based on configuration interaction method

High-level configuration interaction method including the spin-orbit coupling is used to investigate the low-lying excited electronic states of AuB that is not reported experimentally. The electronic structure in our work is preformed through the three steps stated below. First of all, Hartree-Fock method is performed to compute the singlet-configuration wavefunction as the initial guess. Next, we generate a multi-reference wavefunction by using the state-averaged complete active space self-consistent field (SACASSCF). Finally, the wavefunctions from CASSCF are utilized as reference, the exact energy point values are calculated by the explicitly correlated dynamic multi-reference configuration interaction method (MRCI). The Davidson correction (+Q) is put forward to solve the size-consistence problem caused by the MRCI method. To ensure the accuracy, the spin-orbit effect and correlation for inner shell electrons and valence shell electrons are considered in our calculation. The potential energy curves of 12 Λ-S electronic states are obtained. According to the explicit potential energy curves, we calculate the spectroscopic constants through solving radial Schrödinger equation numerically. We analyze the influence of electronic state configuration on the dipole moment by using the variation of dipole moment with nuclear distance. The spin-orbit matrix elements for parts of low-lying exciting states are computed, and the relation between spin-orbit coupling and predissociation is discussed. The predissociation is analyzed by using the obtained spin-orbit matrix elements of the 4 Λ-S states which spilt into 12 Ω states. It indicates that due to the absence of the intersections between the curves of spin-orbit matrix elements related with the 4 low-lying Λ-S states, the predissociation for these low-lying exciting states will not occur. Finally, the properties of optical transition between the ground Ω state <inline-formula><tex-math id="M3">\begin{document}$ {\rm A}^{1}{{{\Pi}}}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M3.png"/></alternatives></inline-formula> and first excited Ω state <inline-formula><tex-math id="M4">\begin{document}$ {{\mathrm{X}}}^{1}{{{\Sigma }}}_{{0}^{+}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M4.png"/></alternatives></inline-formula> are discussed in laser-cooling filed by analyzing the Franck-Condon factors and radiative lifetime. And the transition dipole moment is also calculated. But our results reveal that the AuB is not an ideal candidate for laser-cooling. In conclusion, this work is helpful in deepening the understanding of AuB, especially the structures of electronic states, interaction between excited states, and optical transition properties. All the data presented in this paper are openly available at <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.doi.org/10.57760/sciencedb.j00213.00009">https://www.doi.org/10.57760/sciencedb.j00213.00009</ext-link>.

A multiconfigurational approach to the electronic structure of electro‐generated species of the Re2(μ‐Ph2PCH2PPh2)(S2CNEt2)4 complex

AbstractThe nature of Re−Re bonding in Re2(μ‐Ph2PCH2PPh2)(S2CNEt2)4 complex, including its neutral (10) and two oxidized (1+ and 12+) species, was explored utilizing state‐of‐the‐art quantum chemical methodologies within density functional theory (DFT) and complete active space self‐consistent field (CASSCF). Our results show that the ground state electron configuration of the 10 is with an effective bond order (EBO) of 2.73 computed with CASSCF. The oxidation discloses an electron removal from a metal‐based orbital, giving 1+ and 12+ with an EBO of 2.71 and 2.64, respectively. The relative similarity in EBO values among neutral and oxidized species suggests that the oxidation processes have almost no effect on the Re−Re bond strength even though electrons removal from metal‐based orbitals because the electrons that occupied the components of Re−Re bonds in 1+ and 12+ localized on the two Re ions, thus, they were excluded from EBO estimation.

Excited state energies, orbital energies and virial coefficients in Confined multi-electron systems

In the present study, the electronic structure of neutral He and Li atoms confined at the center of an impenetrable spherical cavity of varying radius has been investigated. Average, state, orbital energies and wave functions for the ground and excited state electron configurations 1snl (1s2nl)[n = 2, 3, 4 and l = 0, 1, 2 and 3] have been calculated using the method that is a combination of quantum genetic algorithm procedure and Hartree-Fock Roothaan. The atomic orbitals built up from Slater-type orbitals are used in calculations. The average state and orbital energies have been calculated for the first time for the higher excited states with nl [n = 3,4 and l = 1,2,3 for confined He atom and n = 3,4 and l = 0, 1,2,3 for confined Li atom]. The results show that impurity charge and spatial confinement have a great impact on orbital energies, average, state energies and virial coefficients of the system, especially in strong confinement region. In addition, it is seen that when cavity radius is extremely large, all state energies and virial coefficients approach the corresponding values of free atom.

External charge compensation in etched gallium nitride measured by x-ray photoelectron spectroscopy

Electronic states at GaN surfaces and at regrowth and heteroepitaxy interfaces inhibit electronic device performance. Understanding electronic state configuration at the GaN surface is, therefore, crucial for the development of GaN-based devices, which are currently of considerable interest in power electronic applications. GaN and other wurtzite III-nitrides possess large spontaneous polarization along the c-axis, producing a bound sheet charge at the surface, which affects the electronic state configuration through the formation of internal and external compensation charges. Defects induced by conventional plasma-based dry etching methods may inhibit the internal screening of this bound charge and thus increase the concentration of external charged states. The surface band bending of n-type Ga-face GaN (0001) was measured with x-ray photoelectron spectroscopy after inductively coupled plasma etching to investigate the impact of dry etching on external charge compensation. GaN samples were etched using inductively coupled plasma with varying rf power and a novel plasma-enhanced atomic layer etching method using an oxidation, fluorination, and ligand-exchange mechanism. The band bending varied from 0.0 to 0.8 ± 0.1 eV for the samples measured.

Understanding the chemical bonding of ground and excited states of HfO and HfB with correlated wavefunction theory and density functional approximations.

Knowledge of the chemical bonding of HfO and HfB ground and low-lying electronic states provides essential insights into a range of catalysts and materials that contain Hf-O or Hf-B moieties. Here, we carry out high-level multi-reference configuration interaction theory and coupled cluster quantum chemical calculations on these systems. We compute full potential energy curves, excitation energies, ionization energies, electronic configurations, and spectroscopic parameters with large quadruple-ζ and quintuple-ζ quality correlation consistent basis sets. We also investigate equilibrium chemical bonding patterns and effects of correlating core electrons on property predictions. Differences in the ground state electron configuration of HfB(X4Σ-) and HfO(X1Σ+) lead to a significantly stronger bond in HfO than HfB, as judged by both dissociation energies and equilibrium bond distances. We extend our analysis to the chemical bonding patterns of the isovalent HfX (X = O, S, Se, Te, and Po) series and observe similar trends. We also note a linear trend between the decreasing value of the dissociation energy (De) from HfO to HfPo and the singlet-triplet energy gap (ΔES-T) of the molecule. Finally, we compare these benchmark results to those obtained using density functional theory (DFT) with 23 exchange-correlation functionals spanning multiple rungs of "Jacob's ladder." When comparing DFT errors to coupled cluster reference values on dissociation energies, excitation energies, and ionization energies of HfB and HfO, we observe semi-local generalized gradient approximations to significantly outperform more complex and high-cost functionals.

原子および分子の電子配置学習のための簡易教材の試作と実践

A simple educational tool was prepared and practiced for learning electronic configuration of atoms and molecules. This tool consisted of an A4 size sheet for the simulation of electronic configuration of an atom on the front side, and that of a molecule on the back side, and sixteen round counting chips (19 mm o.d.) indicating electron spin (s) of a lone and paired electron (s) on the front and back side. This tool was possible to simulate the ground state electron configuration of atoms from hydrogen to zinc, and of homonuclear diatomic molecules from hydrogen to neon on the periodic table. It was inferred that the tool was useful for understanding and explaining these electronic configurations from the results of questionnaires for the first-year students.

Singlet Biradical Versus Triplet Biradical/Zwitterion Characteristics in Isomers of C6 -C5 -C6 -C7 -C6 -Fused Pentacyclic Aromatic Hydrocarbons Revealed through Reactivity Patterns.

Among various polycyclic aromatic hydrocarbons, C6 -C5 -C6 -C7 -C6 fused pentacyclic aromatic hydrocarbons have the unique potential to adopt quinonoid, zwitterion, singlet, or triplet biradical electronic configurations. Two such hybrid structures between pentacene and azulene were synthesized and their ground state electronic configurations were deduced from the reactivity patterns they exhibit respectively. Compound 6, where the radicaloid carbons are linked through a para-phenylene, forms a head-to-head dimer like a singlet biradical. In contrast, isomer 7, where the para-linkage was switched to meta, reacts readily with oxygen which resembles the reactivity of a triplet state. The oxidized intermediate(s) then undergoes rearrangement to furnish the C6 -C5 -C6 -C6 -C6 ring contraction product 13. Cation 14, the protonated form of 7, was synthesized, which implies 7 also reacts like a zwitterion. It was revealed the oxidative rearrangement takes place even with mesityl dibenzotropylium cation despite its perceived aromaticity. DFT calculations confirm the most stable forms of 6 and 7 are singlet and triplet diradical, which is consistent with the observed reactivity of respective molecules.

Antitumor Immune Response Triggered by Metal-Based Photosensitizers for Photodynamic Therapy: Where Are We?

Metal complexes based on transition metals have rich photochemical and photophysical properties that are derived from a variety of excited state electronic configurations triggered by visible and near-infrared light. These properties can be exploited to produce powerful energy and electron transfer processes that can lead to oxygen-(in)dependent photobiological activity. These principles are the basis of photodynamic therapy (PDT), which is a clinically approved treatment that offers a promising, effective, and noninvasive complementary treatment or even an alternative to treat several types of cancers. PDT is based on a reaction involving a photosensitizer (PS), light, and oxygen, which ultimately generates cytotoxic reactive oxygen species (ROS). However, skin photosensitivity, due to the accumulation of PSs in skin cells, has hampered, among other elements, its clinical development and application. Therefore, these is an increasing interest in the use of (metal-based) PSs that are more specific to tumor cells. This may increase efficacy and corollary decrease side-effects. To this end, metal-containing nanoparticles with photosensitizing properties have recently been developed. In addition, several studies have reported that the use of immunogenic/immunomodulatory metal-based nanoparticles increases the antitumor efficacy of immune-checkpoint inhibitor-based immunotherapy mediated by anti-PD-(L)1 or CTLA-4 antibodies. In this review, we discuss the main metal complexes used as PDT PSs. Lastly, we review the preclinical studies associated with metal-based PDT PSs and immunotherapies. This therapeutic association could stimulate PDT.

Electronic and magnetic properties of yttria-stabilized zirconia (6.7 mol% in Y2O3) doped with Er3+ ions from first-principle computations

Yttria-stabilized zirconia (YSZ) is a widely recognized ceramic of distinct electrical, mechanical and optical properties. Although YSZ is an intrinsically paramagnetic solid, it could potentially transform to a magnetic semiconductor by incorporating in its crystalline structure isolated atoms bearing unpaired valence electrons. Based on this hypothesis and motivated by the latest advances on YSZ doped with rare-earth atoms, in the current article we report on the electronic and magnetic properties of YSZ doped with Er3+ ([Xe]4f116s0) cations that comprise three “unpaired” 4f electrons in their ground state electronic configuration. Our computations, conducted on YSZ 6.7 mol% in Y2O3 doped with two different Er3+ concentrations (3.2 and 6.7 mol% in Er2O3), expose that Er3+:YSZ is a stable antiferromagnetic semiconductor (\(S=\frac{3}{2}\) per Er+3) bearing a rather wide band gap of about 5 eV. All results presented and discussed in current report rely on spin–polarized density functional theory (DFT) within the spin resolved generalized gradient approximation (SGGA) for the pure Perdew, Burke and Ernzerhof exchange–correlation functional (PBE) and hybrid version widely referred as PBE0. According to our knowledge, this is the first time that the magnetic properties of Er3+: YSZ materials are reported for any Er+3 concentration.

The Connection between Pseudo-Jahn–Teller Effect and Electron Delocalization for Proving the Origin of Equilibrium Geometry of Nitrosyl Halides (Halides = Cl, Br, and I)

The theoretical calculations on triplet linear and non-linear structures of nitrosyl halides XNO (X = Cl, Br, and I) confirm that the origin of instability and symmetry breaking of XNO linear structures is a pseudo-Jahn–Teller effect (PJTE). However, the PJTE associated with electron delocalization may prove the stability of XNO non-linear structures best. The distortion of high-symmetry (C∞v) configurations in XNOs emerges from mixing the PJT with ground 3Σ– and the excited 3Π states in the Qπ direction, which consequently make the ground state unstable. The PJT problem is formulated in the form (3Σ– + 3Π) $$ \otimes $$ π. The energy difference between high-symmetry C∞v geometries and low-symmetry Cs geometries energy gap between the ground and excited states decreases from ClNO to INO. Also, ΔEPJT (i.e., the difference of energy between the highest occupied molecular orbital (HOMO; LPX), and the lowest unoccupied molecular orbital (LUMO; $$\pi _{{{\text{NO}}}}^{*}$$ )) plays an important role in the instability of structures. Electron delocalization decreases and PJT instability increases from ClNO to INO in high-symmetry C∞v geometries. According to the results of the canonical molecular orbital (CMO) analysis, the contribution of the LPX non-bonding orbitals in the vibronic coupling constant (F) increases from ClNO to INO. Also, the NBODEL results indicate that the instability of compounds increases from ClNO to INO. Because the primary force constant is positive, the curvature of ground electronic state configuration curves in adiabatic potential energy surfaces (APESs) decreases from ClNO to INO. The variations of the chemical hardness differences between the non-linear (Cs) and linear (C∞v) structures decrease from ClNO to INO and of chemical potential differences increase from ClNO to INO, justifying the variation trend of ΔEPJT. Furthermore, based on the obtained results, Δ[η(Cs) – η(C∞v)] obeys the maximum hardness principle.

Interaction of 1,1-Diamino-2,2-Dinitroethylene with Aluminum and Gallium Admixture - DFT Treatment

Interaction of 1,1-diamino-2,2-dinitroethylene with nAl+mGa (n,m:1,2) admixture has been investigated within the constraints of density functional theory at the level of UB3LYP/6-311++G(d,p). Various multiplicity states arise for the composites due to the open-shell ground state electronic configurations of Al and Ga atoms. The composites are electronically stable, thermodynamically exothermic and have favorable Gibbs’ free energy of formation values. Various quantum chemical properties have been obtained and discussed. The calculated UV-VIS spectra indicate that some of the composites are infrared absorbing systems beyond 700 nm.

Natural Orbital Branching Scheme for Time-Dependent Density Functional Theory Nonadiabatic Simulations.

Real time-time-dependent density functional theory (rt-TDDFT) has now been used to study a wide range of problems, from optical excitation to charge transfer, to ion collision, and to ultrafast phase transition. However, conventional rt-TDDFT Ehrenfest dynamics for nuclear movement lacks a few critical features to describe many problems: the detail balance between state transitions, decoherence for the wave function evolution, and stochastic branching of the nuclear trajectory. There are many-body formalisms to describe such nonadiabatic molecular dynamics, especially the ones based on mixed quantum/classical simulations, like the surface hopping and wave function collapsing schemes. However, there are still challenges to implement such many-body formalisms to the rt-TDDFT simulations, especially for large systems where the excited state electronic structure configuration space is large. Here we introduce two new algorithms for nonadiabatic rt-TDDFT simulations: the first is a Boltzmann factor algorithm which introduces decoherence and detailed balance in the carrier dynamics but uses mean field theory for nuclear trajectory. The second is a natural orbital branching (NOB) formalism, which uses a time-dependent density matrix for electron evolution and a natural orbital set to collapse the wave function upon. It provides the features of decoherence, detailed balance, and trajectory branching. We have tested these methods for a molecule radiolysis decay problem. We found that these methods can be used to study such radiolysis problems in which the molecule is broken into many fragments following complex electronic structure transition paths. The computational time of NOB is similar to that of the original plain rt-TDDFT simulations.

In vitro biomolecular interaction studies and cytotoxic activities of copper(II) and zinc(II) complexes bearing ONS donor thiosemicarbazones

Among all the bio‐metals, zinc and copper derivatives of ONS donor thiosemicarbazone have aroused great interest because of their potential biological applications. Multisubstituted thiosemicarbazone ligand H2dspt (3,5‐dichlorosalicylaldehyde‐N4‐phenylthiosemicarbazone) derived new ternary complexes like [Zn(dspt)(phen)]‧DMF (1) and [Cu(dspt)(phen)]‧DMF (2), and another thiosemicarbazone, H2dsct (3,5‐dichlorosalicylaldehyde‐N4‐cyclohexylthiosemicarbazone), derived [Cu(dsct)(bipy)]‧DMF (3). These complexes have been characterized by elemental analysis (CHNS), Fourier transform infrared (FT‐IR), ultraviolet–visible (UV–Vis) and proton nuclear magnetic resonance (1H‐NMR) spectra. The structures of the complexes were obtained by single‐crystal X‐ray diffraction analysis. Compounds1and2got crystallized in the monoclinicP21/cspace group. The complexes showed interesting supramolecular interaction, which in turn stabilizes the complexes. The ground state electronic configurations of the complexes were studied using the B3LYP/LANL2DZ basis set, and ESP plots of complexes were investigated. The interaction of the complexes with calf thymus DNA (CT‐DNA) was studied using absorption and fluorescence spectroscopic methods. A UV study of the interaction of the complexes with calf thymus DNA (CT‐DNA) has shown that the complexes can effectively bind to CT‐DNA, and [Cu(dspt)(phen)]·DMF (2) exhibited the highest binding constant to CT‐DNA (Kb= 3.7 × 104). Fluorescence spectral studies also indicated that Complex2binds relatively stronger with CT DNA through intercalative mode, exhibiting higher binding constant (Kq= 4.7 × 105). The DNA cleavage result showed that the complexes are capable of cleaving the DNA without the help of any external agent. Molecular docking studies were carried out to understand the binding of complexes with the molecular target DNA. Complex2exhibited the highest cytotoxicity against human breast cancer cell line MD‐MBA‐231 (IC50= 23.93 μg/mL) as compared to Complex1(IC50= 44.40 μg/mL).

The Coordination Behaviour of CuI Photosensitizers Bearing Multidentate Ligands Investigated by X-ray Absorption Spectroscopy.

A systematic series of four novel homo‐ and heteroleptic CuI photosensitizers based on tetradentate 1,10‐phenanthroline ligands of the type X^N^N^X containing two additional donor moieties in the 2,9‐position (X=SMe or OMe) were designed. Their solid‐state structures were assessed by X‐ray diffraction. Cyclic voltammetry, UV‐vis absorption, emission and X‐ray absorption spectroscopy were then used to determine their electrochemical, photophysical and structural features in solution. Following, time‐resolved X‐ray absorption spectroscopy in the picosecond time scale, coupled with time‐dependent density functional theory calculations, provided in‐depth information on the excited state electron configurations. For the first time, a significant shortening of the Cu−X distance and a change in the coordination mode to a pentacoordinated geometry is shown in the excited states of the two homoleptic complexes. These findings are important with respect to a precise understanding of the excited state structures and a further stabilization of this type of photosensitizers.

Structures and bonding in [L]M(μ-CCR)2M[L] and [L]M(μ-RC4R)M[L]: requirements for C-C coupling.

A theoretical analysis of [L]M(μ-CCR)2M[L] and [L]M(μ-RC4R)M[L], where M represents the selected elements from the main group, transition metals, lanthanides and actinides, shows how the central (μ-CCR)2 and (μ-RC4R) units reorganize as M traverses across the periodic table. In this context transition metal and actinide complexes are similar in nature, while lanthanide and main group complexes show similarity. The ground state electronic configuration and thus the metal oxidation state control these striking differences. An effective way to stabilize the (iii) oxidation state of thorium in a metallacycle complex is shown for the first time. A strategy is proposed to make a cross-connection between the two sets. The approach used here lends itself to obvious extensions.

Low-Temperature Spectra and Density Functional Theory Modeling of Ru(II)-Bipyridine Complexes with Cyclometalated Ancillary Ligands: The Excited State Spin-Orbit Coupling Origin of Variations in Emission Efficiencies.

The 77 K emission spectra of cyclometalated ruthenium(II)-2,2'-bipyridine (CM-Ru-bpy) chromophores are very similar to those of related Ru-bpy complexes with am(m)ine or diimmine ancillary ligands, and density functional theory (DFT) modeling confirms that the lowest energy triplet metal to ligand charge transfer (3MLCT) excited states of CM-Ru-bpy and related Ru-bpy complexes have very similar electronic configurations. However, the phosphorescence decay efficiencies of CM-Ru-bpy excited states are about twice those of the conventional Ru-bpy analogues. In contrast to the similar 3MLCT excited state electronic configurations of the two classes of complexes, the CM-Ru-bpy chromophores have much broader visible region MLCT absorptions resulting from several overlapping transitions, even at 87 K. The emitting excited-state emission efficiencies depend on spin-orbit coupling (SOC) mediated intensity stealing from singlet excited states, and this work explores the relationship between the phosphorescence efficiency and visible region absorption spectra of Ru-bpy 3MLCT excited states in the weak SOC limit. The intrinsic 3MLCT emission efficiency, ιem, depends on mixing with singlet excited states whose RuIII-dπ-orbital angular momenta differ from that of the emitting state. DFT modeling of the 1MLCT excited-state electronic configurations that contribute significantly to the lowest energy absorption bands have RuIII-dπ orbitals that differ from those of their emitting 3MLCT excited states. This leads to a very close relationship between ιem and the lowest energy MLCT band absorptivities in Ru-bpy chromophores. Thus, the larger number of 1MLCT transitions that contribute to the lowest energy absorption bands accounts for the enhanced phosphorescence efficiency of Ru-bpy complexes with cyclometalated ancillary ligands.

Probing ultrafast C-Br bond fission in the UV photochemistry of bromoform with core-to-valence transient absorption spectroscopy.

UV pump–extreme UV (XUV) probe femtosecond transient absorption spectroscopy is used to study the 268 nm induced photodissociation dynamics of bromoform (CHBr3). Core-to-valence transitions at the Br(3d) absorption edge (∼70 eV) provide an atomic scale perspective of the reaction, sensitive to changes in the local valence electronic structure, with ultrafast time resolution. The XUV spectra track how the singly occupied molecular orbitals of transient electronic states develop throughout the C–Br bond fission, eventually forming radical Br and CHBr2 products. Complementary ab initio calculations of XUV spectral fingerprints are performed for transient atomic arrangements obtained from sampling excited-state molecular dynamics simulations. C–Br fission along an approximately symmetrical reaction pathway leads to a continuous change of electronic orbital characters and atomic arrangements. Two timescales dominate changes in the transient absorption spectra, reflecting the different characteristic motions of the light C and H atoms and the heavy Br atoms. Within the first 40 fs, distortion from symmetry to form a quasiplanar CHBr2 by the displacement of the (light) CH moiety causes significant changes to the valence electronic structure. Displacement of the (heavy) Br atoms is delayed and requires up to ∼300 fs to form separate Br + CHBr2 products. We demonstrate that transitions between the valence-excited (initial) and valence + core-excited (final) state electronic configurations produced by XUV absorption are sensitive to the localization of valence orbitals during bond fission. The change in valence electron-core hole interaction provides a physical explanation for spectral shifts during the process of bond cleavage.

The Role of Pseudo Jahn–Teller Effect in Geometry and Electronic Parameters of Tetrahalodigermene Ge2X4 (X= Cl, Br, I)

The symmetry breaking of molecules depends on its context and origin. It is well shown the pseudo Jahn – Teller effect (PJTE) describes the origin of symmetry breaking of planar configurations. Based on the PJTE theory, the configurations, electronic parameters and conformational changes in molecular systems are predicted. Optimization of the D2h and C2h configurations of tetrahalodigermene Ge2X4 (X = Cl, Br, I) by ab initio calculations showed that the C2h configurations are more stable than planar ones. The different energy between high-symmetry D2h geometries and low-symmetry C2h geometries decrease from Ge2Cl4 to Ge2I4. Instability of the high-symmetry D2h configurations is arising from the PJT coupling of the ground Ag state and the exited B2g state in the Qb2g direction. The PJTE problem $$({{A}_{g}} + {{B}_{{2g}}}) \otimes {{b}_{{2g}}}$$ creates stable geometries of Ge2X4 (X = Cl, Br, I) analogs with C2h configurations. It is expected that when the energy gap between the desired states with D2h configurations decreases, the PJT stabilization energy (EPJT) increases. Despite this expectation, with increasing the energy gap from Ge2Cl4 to Ge2I4, EPJT decreases. According to the results of the canonical molecular orbital (CMO) analysis, the contributions of the b3u and b1u molecular orbitals in the vibronic coupling constant (F) decrease from Ge2Cl4 to Ge2I4. Consequently, assuming the primary force constant is positive, the negative curvatures of ground state electronic configuration curves in adiabatic potential energy surfaces (APESs) decreases from Ge2Cl4 to Ge2I4. The trend observed for the variations of the chemical hardness (η) of Ge2X4 analogs obey the maximum hardness principle.