Pseudo Jahn-Teller Distortion Research Articles

Oxygen vacancy-induced plasmonic and polaronic excitations in rubidium- and potassium-doped hexagonal tungsten bronzes

Potassium- and rubidium-doped hexagonal tungsten bronzes (K- and Rb-HTBs) were examined in comparison with cesium-doped hexagonal tungsten bronze (Cs-HTB) for their crystal structure and dielectric functions via spectrophotometry, spectroscopic ellipsometry, X-ray diffraction, and X-ray photoelectron spectroscopy. A substantial amount of oxygen vacancy (VO) was detected in all HTBs via chemical analysis, which increased depending on the dopant K → Rb → Cs. A minute (201) peak appeared for K- and Rb-HTBs, indicating symmetry transition from P63/mcm to P6322 due to the pseudo Jahn–Teller distortion; this suggests that K- and Rb-HTBs contain lesser conduction electrons than Cs-HTB. Double-peaked loss functions were decomposed using the Drude−Lorentz theory, and the associated plasma frequency, polaron energies, and W5+ fractions increased as the dopants changed, K → Rb → Cs, with increasing VO content. The origin of the decreased VO content in K- and Rb-HTBs was discussed in relation to water-related defects on prismatic planes.

White-light emission triggered by pseudo Jahn–Teller distortion at the pressure-induced phase transition in Cs4PbBr6

The study of Cs4PbBr6 revealed an unusual pressure-induced increase in the volume of PbBr6 octahedra originating from the pseudo-Jahn–Teller effect that triggers white-light emission above 3.2 GPa.

Harnessing Pseudo-Jahn-Teller Disordering of Monoclinic Birnessite for Excited Interfacial Polarization and Local Magnetic Domains.

The symmetry in a polymorph is one of the most important elements for determining the inherent lattice nature. The MnO2 host tends to high-symmetry MnO6 octahedra as a result of the electronic structure t2g 3 eg 0 of Mn4+ ions, displaying an ordered structure accompanying with poor polarization loss and limiting its application toward high-performance microwave absorbers. Here, a pseudo-Jahn-Teller (PJT) distortion and PJT disordering design with abundant self-forming interfaces and local magnetic domains in the monoclinic birnessite-MnO2 host is first reported. The PJT distortion can give rise to asymmetric MnO6 octahedra, inducing the formation of interfaces and increased electron spin magnetic moment in the lattice. The resultant birnessite with PJT distortions and PJT disordering delivers an outstanding reflection loss value of -42.5dB at an ultralow thickness of 1.7mm, mainly derived from the excited interfacial polarization and magnetic loss. This work demonstrates an effective approach in regulating the lattice structure of birnessite for boosting microwave absorption performance.

Cooperative Pseudo Jahn Teller distortion derives phase transitions in bismuth oxide

Bismuth oxide exhibits a complex array of structures with a broad range of properties of various technological importance. We derive the phase transition pathway using the in-situ heating X-ray diffraction data, evidencing four polymorphs of α, β, δ, and γ. We prove that the observed phase transitions are due to the cooperative pseudo-Jahn-Teller distortion in the crystal originating from mixing the ground state Bi6s and excited Bi6p states. Using the electron localization function and crystal orbital theory, we explore the role of the Bi3+ lone pair in the second-order phase transition. It is found that the O2p states have a critical role in stabilizing the lone pair activity, which leads to a pseudo-Jahn Teller distortion cooperatively inducing the phase transition.

Excited-State Distortions Promote the Photochemical 4π-Electrocyclizations of Fluorobenzenes via Machine Learning Accelerated Photodynamics Simulations.

Benzene fluorination increases chemoselectivities for Dewar-benzenes via 4π-disrotatory electrocyclization. However, the origin of the chemo- and regioselectivities of fluorobenzenes remains unexplained because of the experimental limitations in resolving the excited-state structures on ultrafast timescales. The computational cost of multiconfigurational nonadiabatic molecular dynamics simulations is also currently cost-prohibitive. We now provide high-fidelity structural information and reaction outcome predictions with machine-learning-accelerated photodynamics simulations of a series of fluorobenzenes, C6 F6-n Hn , n=0-3, to study their S1 →S0 decay in 4 ns. We trained neural networks with XMS-CASPT2(6,7)/aug-cc-pVDZ calculations, which reproduced the S1 absorption features with mean absolute errors of 0.04 eV (<2 nm). The predicted nonradiative decay constants for C6 F4 H2 , C6 F6 , C6 F3 H3 , and C6 F5 H are 116, 60, 28, and 12 ps, respectively, in broad qualitative agreement with the experiments. Our calculations show that a pseudo Jahn-Teller distortion of fluorinated benzenes leads to an S1 local-minimum region that extends the excited-state lifetimes of fluorobenzenes. The pseudo Jahn-Teller distortions reduce when fluorination decreases. Our analysis of the S1 dynamics shows that the pseudo-Jahn-Teller distortions promote an excited-state cis-trans isomerization of a πC-C bond. We characterized the surface hopping points from our NAMD simulations and identified instantaneous nuclear momentum as a factor that promotes the electrocyclizations.

Substituent effects on the photophysical properties of 2,9-substituted phenanthroline copper(I) complexes: a theoretical investigation.

The electronic and nuclear structures of a series of [Cu(2,9-(X)2 -phen)2 ]+ copper(I) complexes (phen=1,10-phenanthroline; X=H, F, Cl, Br, I, Me, CN) in their ground and excited states are investigated by means of density functional theory (DFT) and time-dependent (TD-DFT) methods. Subsequent Born-Oppenheimer molecular dynamics is used for exploring the T1 potential energy surface (PES). The T1 and S1 energy profiles, which connect the degenerate minima induced by ligand flattening and Cu-N bond symmetry breaking when exciting the molecule are calculated as well as transition state (TS) structures and related energy barriers. Three nuclear motions drive the photophysics, namely the coordination sphere asymmetric breathing, the well-documented pseudo Jahn-Teller (PJT) distortion and the bending of the phen ligands. This theoretical study reveals the limit of the static picture based on potential energy surfaces minima and transition states for interpreting the luminescent and TADF properties of this class of molecules. Whereas minor asymmetric Cu-N bonds breathing accompanies the metal-to-ligand-charge-transfer re-localization over one or the other phen ligand, the three nuclear movements participate to the flattening of the electronically excited complexes. This leads to negligible energy barriers whatever the ligand X for the first process and significant ligand dependent energy barriers for the formation of the flattened conformers. Born-Oppenheimer (BO) dynamics simulation of the structural evolution on the T1 PES over 11 ps at 300 K confirms the fast backwards and forwards motion of the phenanthroline within 200-300 fs period and corroborates the presence of metastable C2 structures.

Magnetoelectric effect arising from a field-induced pseudo Jahn-Teller distortion in a rare-earth magnet

Magnetoelectric materials are attractive for several applications, including actuators, switches, and magnetic field sensors. Typical mechanisms for achieving a strong magnetoelectric coupling are rooted in transition metal magnetism. In sharp contrast, here we identify $\mathrm{CsEr}{({\mathrm{MoO}}_{4})}_{2}$ as a magnetoelectric material without magnetic transition metal ions, thus ensuring that the Er ions play a key role in achieving this interesting property. Our detailed study includes measurements of the structural, magnetic, and magnetoelectric properties of this material. Bulk characterization and neutron powder diffraction show no evidence for structural phase transitions down to 0.3 K and therefore $\mathrm{CsEr}{({\mathrm{MoO}}_{4})}_{2}$ maintains the room temperature $P2/c$ space group over a wide temperature range without external magnetic field. These same measurements also identify collinear antiferromagnetic ordering of the ${\mathrm{Er}}^{3+}$ moments below ${T}_{N}=0.87\phantom{\rule{4pt}{0ex}}\mathrm{K}$. Complementary dielectric constant and pyroelectric current measurements reveal that a ferroelectric phase with a maximum polarization $P\ensuremath{\sim}0.6\phantom{\rule{4pt}{0ex}}\mathrm{nC}/{\mathrm{cm}}^{2}$ emerges when applying a modest external magnetic field, which indicates that this material has a strong magnetoelectric coupling. We argue that the magnetoelectric coupling in this system arises from a pseudo Jahn-Teller distortion induced by the magnetic field.

Crystal structure and magnetism in theS= 1/2 spin dimer compound NaCu2VP2O10

The crystal structure of the spin dimer magnet NaCu2VP2O10 was determined using single-crystal X-ray diffraction and electron diffraction. NaCu2VP2O10 displayed a non-centrosymmetric orthorhombic C2221 structure with a = 6.13860 (10) Å, b = 14.4846 (3) Å and c = 8.2392 (2) Å. The layered structure comprised CuO4 plaquettes, VO6 octahedra and PO4 tetrahedra. A pair of CuO4 plaquettes formed Cu2O6 structural dimers through edge sharing. The Cu-Cu network formed a distorted puckered-layer structure with pseudo-one-dimensional characteristics. Maximum magnetic susceptibility was observed at ∼60 K and NaCu2VP2O10 became non-magnetic upon further cooling. The spin gap between the spin-singlet non-magnetic ground state and triplet excited state was estimated to be 43.4 K. Thus, NaCu2VP2O10 was assumed to be an alternating chain system with a singlet ground state of dimer origin. The V5+ ions in the VO6 octahedra showed large off-centre displacements along the [110] direction in the primitive perovskite structure, which were attributed to the pseudo-Jahn-Teller distortion of d 0 transition metals.

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy.

Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine FeI dopant ions to be linearly coordinated, occupying a D6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L2,3-edge XAS from which the energy reduction of 3dz2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L3-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm−1), that corresponds with Orbach relaxation via the first excited, MJ = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.

Analysis of pseudo jahn–teller distortion based on natural bond orbital theory: Case study for silicene

Ground state (GS) instability of nondegenerate molecules in high symmetric structures is understood through Pseudo Jahn-Teller mixing of the electronic states through the vibronic coupling. The general approach involves setting up of a Pseudo Jahn-Teller (PJT) problem wherein one or more symmetry allowed excited states couple to the GS to create vibrational instability along a normal mode. This faces two major complications namely (1) estimating the adiabatic potential energy surfaces for the excited states which are often difficult to describe in case the excited states have charge-transfer or multi-excitonic (ME) character and (2) finding out how many such excited states (all satisfying the symmetry requirements for vibronic coupling) of increasing energies need to be coupled with the GS for a particular PJT problem. An analogous alternative approach presented here for the well-known case of symmetry breaking of planar (D6h ) hexasilabenzene (Si6 H6 ) to the buckled (D3d ) structure involves identifying the second-order donor-acceptor, hyperconjugative interactions (E2 i → j ) that stabilize the distorted structure. Following the recent work of Nori-Shargh and Weinhold, one observes that the orbitals involved in the vibronic coupling between the S0 /Sn states and those for the donor (filled)-acceptor (empty) interactions are identical. In fact, deletion of any particular pair of E2 i → j interaction creates vibrational instability in the buckled structure and as a corollary, deleting it for the planar structure removes its instability. The one-to-one correlation between the natural bond orbital theory and PJT theory assists in an intuitive identification of the relevant (few) excited states from a manifold of computed ones that cause symmetry breaking by vibronic coupling. © 2019 Wiley Periodicals, Inc.

Vibrational Control of Covalency Effects Related to the Active Sites of Molybdenum Enzymes.

A multitechnique spectroscopic and theoretical study of the Cp2M(benzenedithiolato) (M = Ti, V, Mo; Cp = η5-C5H5) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin molybdenum enzymes. This work explains the magnitude of the dithiolene folding distortion and the concomitant changes in metal-ligand covalency that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn-Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arises from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance Raman, magnetic circular dichroism, electron paramagnetic resonance, and UV photoelectron spectroscopies to explore the electronic states involved in the vibronic coupling mechanism. Comparison between the UV photoelectron spectroscopy (UPS) of the d2 M = Mo complex and the resonance Raman spectra of the d1 M = V complex reveals the power of this combined spectroscopic approach. Here, we observe that the UPS spectrum of Cp2Mo(bdt) contains an intriguing vibronic progession that is dominated by a "missing-mode" that is composed of PJT-active distortions. We discuss the relationship of the PJT distortions to facile electron transfer in molybdenum enzymes.

Destabilization of pseudo-Jahn–Teller distortion in cesium-doped hexagonal tungsten bronzes

In Cs-doped hexagonal tungsten bronzes (Cs-HTBs), X-ray diffraction–Rietveld analysis has revealed that an increase in the alkali dopant and oxygen vacancies (VO) elongate the c-axis, contract the a-axis, and decrease the deviations of the W–O distance and W coordinates from those of a regular WO6 octahedron. These structural changes are interpreted as a destabilization of pseudo-Jahn–Teller (PJT) distortion by electron donation from Cs+ and VO. A dramatic difference is observed in the destabilization efficiency between the donated electrons from Cs+ and VO, suggesting that the former and latter electrons should be delocalized and localized, respectively. First-principles density functional theory calculations using optB86b-vdW functionals reproduced the behavior of c-axis elongation and a-axis contraction by Cs doping. The projected orbital density of states indicates that the Cs-derived electrons are donated to W-5dyz and W-5dzx orbitals to extend along the c-axis, whereas the VO-derived electrons are donated to W-5dxy and W-5dx2−y2 orbitals to strongly localize in the a–b plane. In HTBs, an anisotropic increase and decrease in the t2g* antibonding electrons from the doped alkali are concluded to induce the anisotropic structural change in PJT distortions.

Pseudo-Jahn-Teller Distortion in Two-Dimensional Phosphorus: Origin of Black and Blue Phases of Phosphorene and Band Gap Modulation by Molecular Charge Transfer.

Phosphorene (Pn) is stabilized as a layered material like graphite, yet it possess a natural direct band gap (Eg = 2.0 eV). Interestingly, unlike graphene, Pn exhibits a much richer phase diagram which includes distorted forms like the stapler-clip (black Pn, α form) and chairlike (blue Pn, β form) structures. The existence of these phases is attributed to pseudo-Jahn-Teller (PJT) instability of planar hexagonal P6(6-) rings. In both cases, the condition for vibronic instability of the planar P6(6-) rings is satisfied. Doping with electron donors like tetrathiafulvalene and tetraamino-tetrathiafulvalene and electron acceptors like tetracyanoquinodimethane and tetracyanoethylene convert blue Pn into N-type and black Pn into efficient P-type semiconductors, respectively. Interestingly, pristine blue Pn, an indirect gap semiconductor, gets converted into a direct gap semiconductor on electron or hole doping. Because of comparatively smaller undulation in blue Pn (with respect to black Pn), the van der Waals interactions between the dopants and blue Pn is stronger. PJT distortions for two-dimensional phosphorus provides a unified understanding of structural features and chemical reactivity in its different phases.

Steric and electric field driven distortions in aromatic molecules: spontaneous and non-spontaneous symmetry breaking.

The structures of molecules form the cornerstone of our chemical knowledge. Lowering of symmetry in closed-shell molecules is often attributed to the Pseudo Jahn-Teller (PJT) distortions wherein non-adiabatic coupling (NAC) between the ground state and excited states creates vibrational instability along specific normal modes. Nevertheless, other factors like steric interactions are also well known in the literature to induce structural distortions. In this article, we consider two specific cases of molecular distortions - the first one being spontaneous for contorted polyaromatic hydrocarbons (c-PAH) where non-bonded repulsions between the two pairs of syn H-atoms in tribenzopyrene, TBP (1), can enforce either a C2v → C2 or C2v → Cs distortion. PJT-effects account for the correct preference of the Cs structure over C2 (by 4.6 kcal mol-1). The second case (non-spontaneous symmetry breaking) is that of benzene (2) and coronene (3) which upon application of sufficiently strong static external electric field develop vibrational instability along q(a2u) to cause D6h → C6v and D6h → C2 distortions for 2 and 3 respectively. An external electric field (FZ) was applied parallel to the aromatic ring of 2-3 for investigation of non-spontaneous symmetry breaking. Such electric field induced structural distortion is understood on the basis of excess charge accumulation of the planar rings which is circumvented by symmetry lowering. PJT effects seem to have significant consequences for identification of global minima amongst several local minimal molecular structures.

1,4-Dithiine—Puckered in the Gas Phase but Planar in Crystals: Role of Cooperativity

Tricyclic C6S8 is known to exist in two different polymorphic phases, namely, alpha (α) and beta (β) forms with planar and puckered conformations, respectively. Recently, it has been shown that the individual molecule undergoes spontaneous symmetry breaking due to pseudo-Jahn–Teller (PJT) distortion resulting in a puckered conformation at the ground state. Here, on the basis of solid-state dispersion-corrected DFT, DFT-D2, as well as the localized Gaussian basis calculations, on periodic systems, we have compared the relative stabilities and structural preferences for α and β polymorphs in a systematic way, starting from the monomers to different forms of higher aggregates in both α and β crystals. From the molecular viewpoint, puckered conformations of the β form are found to be more stable compared to that of planar ones in the α form. Nevertheless, it is shown that PJT distortion can be suppressed by increasing the π-stacking interactions in its aggregates along the crystallographic c-axis and, therefo...

Pseudo Jahn–Teller Origin of Buckling Distortions in Two-Dimensional Triazine-Based Graphitic Carbon Nitride (g-C3N4) Sheets

Due to its direct band gap and light mass, the recently synthesized triazine-based, graphitic carbon nitride (TGCN) is considered a promising material for future microelectronics. However, despite the structural similarity with completely planar carbon-only graphene, TGCN sheets are different because of the presence of buckling distortions making the TGCN sheets nonplanar. In this article, we show that the sufficiently strong coupling between the unoccupied molecular orbitals (UMOs) with occupied molecular orbitals (OMOs) leads to pseudo Jahn–Teller distortions (PJT) and consequent buckling of TGCN layers. Doping the TGCN with doubly charged cations such as Be2+ can suppress the PJT distortions resulting in a completely planar structure. A proper understanding of the mechanism of the PJT effect in TGCN is crucial for tailoring properties that are relevant for practical applications.

Pseudo Jahn–Teller distortion for a tricyclic carbon sulfide (C6S8) and its suppression in S-oxygenated dithiine (C4H4(SO2)2)

The tricyclic carbon-sulfide, C6S8 molecule containing two S-atoms in the 1,4-position of the central six-membered ring and one disulfide (SS) and one thione (CS) bond on the five membered rings on its either side (1) possesses a “butterfly flapping” type distorted ground state in the gas-phase and also in β-phase of the crystal. For the isolated molecule, better consideration of the S…S non-bonding interactions in the dithiine ring in the bent form at the M06-2X/6-31+G(d,p) level leads to a significant barrier for inversion of 2.4kcal/mol which is 2–3 times more than that previously obtained by Weber and Dolg at the B3LYP/cc-pVTZ level due to underestimation of dispersion interactions at the B3LYP level. The origin of the distortion leading to lowering of symmetry for 1 (C2h→C2) is traced to vibronic mixing between the ground state (Ag) and the low lying excited states of Au symmetry through the au normal mode, a (1Ag+1Au+2Au+3Au)×au pseudo Jahn–Teller effect (PJTE) problem. Based on fitting of the ground state APES to the lowest root of the 4×4 secular determinant, we calculate the linear vibronic coupling constants (F0i) between the relevant states. Similar in class to 1, the S-oxygenated derivative of dithiine, C4H4(SO2)2 (2) unlike most other dithiines, remains planar. The absence of the butterfly-type puckered structure in 2 is traced to the enhanced gap (Δ0) and very small vibronic coupling (F01) between the ground and PJT active state along the au distortion which suppress the PJT instability. Considering the separation of the occupied molecular orbital (OMO) and unoccupied molecular orbitals (UMO) energy levels provide a qualitative understanding for the contrasting behavior of 1 and 2. In effect, the PJT effect is shown to be a fruitful and general tool to describe the presence or lack of molecular distortion.

Transient Absorption Dynamics of Sterically Congested Cu(I) MLCT Excited States

Subpicosecond through supra-nanosecond transient absorption dynamics of the homoleptic Cu(I) metal-to-ligand charge transfer (MLCT) photosensitizers including the benchmark [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) chromophore, as well as [Cu(dsbp)2](+) (dsbp =2,9-di(sec-butyl)-1,10-phenanthroline and [Cu(dsbtmp)2](+) (dsbtmp =2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline) were investigated in dichloromethane and tetrahydrofuran solutions. Visible and near-IR spectroelectrochemical measurements of the singly reduced [Cu(dsbp)2](+) and [Cu(dsbtmp)2](+) species were determined in tetrahydrofuran, allowing for the identification of redox-specific phenanthroline-based radical anion spectroscopic signatures prevalent in the respective transient absorption experiments. This study utilized four different excitation wavelengths (418, 470, 500, and 530 nm) to elucidate dynamics on ultrafast times scales spanning probe wavelengths ranging from the UV to the near-IR (350 to 1450 nm). With the current time resolution of ∼150 fs, initial excited state decay in all three compounds was found to be independent of excitation wavelength. Not surprisingly, there was little to no observed influence of solvent in the initial stages of excited state decay in any of these molecules including [Cu(dmp)2](+), consistent with results from previous investigators. The combined experimental data revealed two ranges of time constants observed on short time scales in all three MLCT chromophores and both components lengthen as a function of structure in the following manner: [Cu(dsbtmp)2](+) < [Cu(dsbp)2](+) < [Cu(dmp)2](+). The molecule with the most inhibited potential for distortion, [Cu(dsbtmp)2](+), possessed the fastest ultrafast dynamics as well as the longest excited state lifetimes in both solvents. These results are consistent with a small degree of excited state distortion, rapid intersystem crossing, and weak vibronic coupling to the ground state. The concomitant systematic variation in both initial time constants, assigned to pseudo-Jahn-Teller distortion and intersystem crossing, suggest that both processes are intimately coupled in all molecules in the series. The variability in these time scales illustrate that strongly impeded structural distortion in Cu(I) MLCT excited state enables more rapid surface crossings in the initial deactivation dynamics.

A Quantum Dynamics Study of the Ultrafast Relaxation in a Prototypical Cu(I)–Phenanthroline

The ultrafast nonadiabatic dynamics of a prototypical Cu(I)-phenanthroline complex, [Cu(dmp)2](+) (dmp = 2,9-dimethyl-1,10-phenanthroline), initiated after photoexcitation into the optically bright metal-to-ligand charge-transfer (MLCT) state (S3) is investigated using quantum nuclear dynamics. In agreement with recent experimental conclusions, we find that the system undergoes rapid (∼100 fs) internal conversion from S3 into the S2 and S1 states at or near the Franck-Condon (FC) geometry. This is preceded by a dynamic component with a time constant of ∼400 fs, which corresponds to the flattening of the ligands associated with the pseudo Jahn-Teller distortion. Importantly, our simulations demonstrate that this latter aspect is in competition with subpicosecond intersystem crossing (ISC). The mechanism for ISC is shown to be a dynamic effect, in the sense that it arises from the system traversing the pseudo Jahn-Teller coordinate where the singlet and triplet states become degenerate, leading to efficient crossing. These first-principles quantum dynamics simulations, in conjunction with recent experiments, allow us to clearly resolve the mechanistic details of the ultrafast dynamics within [Cu(dmp)2](+), which have been disputed in the literature.

Anisotropic strain and Jahn-Teller effect of chiral complexes and metal oxides

For about a decade, we have systematically investigated thermally-accessible lattice strain and local pseudo Jahn-Teller distortion of [CuL2]3[M(CN)6]2·4H2O (L = (1R, 2R)-cyclohexanediamine; M = Cr, Co, and Fe). In mononuclear Cu(II) complexes, (pseudo) Jahn-Teller effect plays an important role in flexible distortion of crystal structures especially Cu(II) coordination environment. Beside Jahn-Teller distortion, we have dealt with some factors for example, metal substitution as bimetallic assemblies, chirality of ligands, and H/D isotope effect to vary intermolecular interaction and crystal packing. According to the course work using variable temperature PXRD, we have found that anisotropy of crystal strain distortion did not corporate with Jahn-Teller distortion around local coordination environment because of the discrepancy of the crystallographic axes and molecular alignment. In order to elucidate the anisotropic control of lattice strain and Jahn-Teller distortion closely, we have employed transition metal oxide with orthogonal or layered structures to prepare composite materials with the chiral metal complexes for discussion of thermally-accessible PXRD changes and IR shift due to adsorption. At first, we have employed chiral one-dimensional zig-zag Cu-Cr bimetallic assemblies and their oxides prepared by burining. Based on variable temperature XRD patterns, a linear correlation (lnK = a/T + b) of K (=d(T)-d(0)/d(T)) values, where d(T) and d(0) are spacing of lattice plane (d = nλ/(2sinθ)) at T K and 0 K (extrapolated), respectively, and its deviation from ideal correlation indicates degree of anisotropic lattice distortion of the composite materials. For example, we could observe LiMnO2, typical material of lithium ion battery, was enhanced anisotropic lattice strain along the b axis or the (011) plane added by [CuL2(H2O)2](NO3)2 complexes. Which may prevent from breaking down regular crystal structures during charge-discharge of secondary battery.