Search

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1′-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3′,5′-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics. [ABSTRACT FROM AUTHOR]

Conical intersections (CIs) play a crucial role in photochemical reactions, offering an efficient channel for ultrafast non-adiabatic relaxation of excited states. This significantly influences the reaction pathways and the resulting products. In this work, we utilize the non-Markovian stochastic Schrödinger equation with complex modes method to explore the dynamics of electronic transitions through conical intersections (CIs) in pyrazine. The linear vibronic coupling model serves as the foundational framework, incorporating both intra-state and inter-state electron–vibrational interactions. The dynamics of the excited electronic transitions are analyzed across varying strengths of system–bath coupling and different bath relaxation times. The accuracy of this method is demonstrated by comparing its predictions with those from the hierarchical equations of motion method. [ABSTRACT FROM AUTHOR]

In the recently discovered proton-coupled energy transfer (PCEnT) mechanism, the transfer of electronic excitation energy between donor and acceptor chromophores is coupled to a proton transfer reaction. Herein, we develop a general theory for PCEnT and derive an analytical expression for the nonadiabatic PCEnT rate constant. This theory treats the transferring hydrogen nucleus quantum mechanically and describes the PCEnT process in terms of nonadiabatic transitions between reactant and product electron–proton vibronic states. The rate constant is expressed as a summation over these vibronic states, and the contribution of each pair of vibronic states depends on the square of the vibronic coupling as well as the spectral convolution integral, which can be viewed as a generalization of the Förster-type spectral overlap integral for vibronic rather than electronic states. The convolution integral also accounts for the common vibrational modes shared by the donor and acceptor chromophores for intramolecular PCEnT. We apply this theory to model systems to investigate the key features of PCEnT processes. The excited vibronic states can contribute significantly to the total PCEnT rate constant, and the common modes can either slow down or speed up the process. Because the pairs of vibronic states that contribute the most to the PCEnT rate constant may correspond to spectroscopically dark states, PCEnT could occur even when there is no apparent overlap between the donor emission and acceptor absorption spectra. This theory will assist in the interpretation of experimental data and will guide the design of additional PCEnT systems. [ABSTRACT FROM AUTHOR]

Accurate quantum dynamics simulations of nonadiabatic processes are important for studies of electron transfer, energy transfer, and photochemical reactions in complex systems. In this comparative study, we benchmark various approximate nonadiabatic dynamics methods with mapping variables against numerically exact calculations based on the tensor-train (TT) representation of high-dimensional arrays, including TT-KSL for zero-temperature dynamics and TT-thermofield dynamics for finite-temperature dynamics. The approximate nonadiabatic dynamics methods investigated include mixed quantum–classical Ehrenfest mean-field and fewest-switches surface hopping, linearized semiclassical mapping dynamics, symmetrized quasiclassical dynamics, the spin-mapping method, and extended classical mapping models. Different model systems were evaluated, including the spin-boson model for nonadiabatic dynamics in the condensed phase, the linear vibronic coupling model for electronic transition through conical intersections, the photoisomerization model of retinal, and Tully's one-dimensional scattering models. Our calculations show that the optimal choice of approximate dynamical method is system-specific, and the accuracy is sensitively dependent on the zero-point-energy parameter and the initial sampling strategy for the mapping variables. [ABSTRACT FROM AUTHOR]

The potential energy surface of tetrazolyl [cyclic (N4CH)] has a conical intersection seam between the two lowest-energy electronic states near the ground state minimum geometry. This work treats that molecule. The potential energy surfaces used in this study are based on a least-squares fitting procedure that includes ab initio energies, energy gradients, and derivative couplings described using polynomials up to fourth-order and ab initio data obtained from multireference configuration interaction wave functions. A five-electronic-state description was generated with a root mean square absolute energy error of 9.6 cm–1, compared to 326.8 cm–1 when only second-order terms were used. The time-independent multimode vibronic coupling in the KDC approximation was used to simulate and analyze the anion ultraviolet photoelectron spectrum of tetrazolide. [ABSTRACT FROM AUTHOR]

In the previous work [Reddy et al., J. Chem. Phys. 151, 044307 (2019)], we have analyzed the dynamics of the intramolecular singlet fission process in a series of prototypical pentacene-based dimers, where the pentacene monomers are covalently bonded to a phenylene linker in ortho, meta, and para positions. The results obtained were qualitatively consistent with the experimental data available, showing an ultrafast population of the multiexcitonic state that mainly takes place via a mediated (superexchange-like) mechanism involving charge transfer and doubly excited states. Our results also highlighted the instrumental role of molecular vibrations in the process as a sizable population of the multiexcitonic state could only be obtained through vibronic coupling. Here, we extend these studies and investigate the effect of the laser field on the dynamics of intramolecular singlet fission by explicitly including the coupling to the laser field in our model. In this manner, and by selectively tuning the laser field to the different low-lying absorption bands of the systems investigated, we analyze the wavelength dependence of the intramolecular singlet fission process. In addition, we have also analyzed how the nature of the initially photoexcited electronic state (either localized or delocalized) affects its dynamics. Altogether, our results provide new insights into the design of intramolecular singlet fission-active molecules. [ABSTRACT FROM AUTHOR]

Quantum dynamics simulations are becoming a powerful tool for understanding photo-excited molecules. Their poor scaling, however, means that it is hard to study molecules with more than a few atoms accurately, and a major challenge at the moment is the inclusion of the molecular environment. Here, we present a proof of principle for a way to break the two bottlenecks preventing large but accurate simulations. First, the problem of providing the potential energy surfaces for a general system is addressed by parameterizing a standard force field to reproduce the potential surfaces of the molecule's excited-states, including the all-important vibronic coupling. While not shown here, this would trivially enable the use of an explicit solvent. Second, to help the scaling of the nuclear dynamics propagation, a hierarchy of approximations is introduced to the variational multi-configurational Gaussian method that retains the variational quantum wavepacket description of the key quantum degrees of freedom and uses classical trajectories for the remaining in a quantum mechanics/molecular mechanics like approach. The method is referred to as force field quantum dynamics (FF-QD), and a two-state ππ*/nπ* model of uracil, excited to its lowest bright ππ* state, is used as a test case. [ABSTRACT FROM AUTHOR]

Quantum dynamics simulations are becoming a standard tool for simulating photo-excited molecular systems involving a manifold of coupled states, known as non-adiabatic dynamics. While these simulations have had many successes in explaining experiments and giving details of non-adiabatic transitions, the question remains as to their predictive power. In this work, we present a set of quantum dynamics simulations on cyclobutanone using both grid-based multi-configuration time-dependent Hartree and direct dynamics variational multi-configuration Gaussian methods. The former used a parameterized vibronic coupling model Hamiltonian, and the latter generated the potential energy surfaces on the fly. The results give a picture of the non-adiabatic behavior of this molecule and were used to calculate the signal from a gas-phase ultrafast electron diffraction (GUED) experiment. Corresponding experimental results will be obtained and presented at a later stage for comparison to test the predictive power of the methods. The results show that over the first 500 fs after photo-excitation to the S2 state, cyclobutanone relaxes quickly to the S1 state, but only a small population relaxes further to the S0 state. No significant transfer of population to the triplet manifold is found. It is predicted that the GUED experiments over this time scale will see signals related mostly to the C–O stretch motion and elongation of the molecular ring along the C–C–O axis. [ABSTRACT FROM AUTHOR]

In this article, we show that the collective light–matter strong coupling regime where N molecular emitters couple to the photon mode of an optical cavity can be mapped to a quantum impurity model where the photon is the impurity that is coupled to a bath of anharmonic transitions. In the thermodynamic limit where N ≫ 1, we argue that the bath can be replaced with an effective harmonic bath, leading to a dramatic simplification of the problem into one of the coupled harmonic oscillators. We derive simple analytical expressions for linear optical spectra (transmission, reflection, and absorption) where the only molecular input required is the molecular linear susceptibility. This formalism is applied to a series of illustrative examples, showing the role of temperature, disorder, vibronic coupling, and optical saturation of the molecular ensemble, explaining that it is useful even when describing an important class of nonlinear optical experiments. For completeness, we provide Appendixes A–C that include a self-contained derivation of the relevant spectroscopic observables for arbitrary anharmonic systems (for both large and small N) within the rotating-wave approximation. While some of the presented results herein have already been reported in the literature, we provide a unified presentation of the results as well as new interpretations that connect powerful concepts in open quantum systems and linear response theory with molecular polaritonics. [ABSTRACT FROM AUTHOR]

The vibronic structure and nuclear dynamics in the first five excited singlet electronic states of bithiophene (2T) are investigated here. Specifically, considerations are given to comprehend the first two structureless and broad electronic absorption bands and the role of nonadiabatic coupling in the excited state relaxation mechanism of 2T in the gas phase. Associated potential energy surfaces (PESs) are established by constructing a model vibronic coupling Hamiltonian using 18 vibrational degrees of freedom and extensive ab initio electronic structure calculations. The topographies of these PESs are critically examined, and multiple conical intersections are established. The nuclear dynamics calculations are performed by propagating wave packets on the coupled electronic manifold. The present theoretical results are in good agreement with the experimental observations. It is found that strong nonadiabatic coupling between the S1–S4 and S1–S5 states along totally symmetric modes is predominantly responsible for the structureless and broad first absorption band, and overlapping S2, S3, S4, and S5 states form the second absorption band. Photorelaxation from the highly excited S5 to the lowest S1 state takes place through a cascade of diabatic population transfers among the S1–S4–S5 electronic manifold within the first ∼100 fs. Totally symmetric C=C stretching, C–S stretching, C–H wagging, ring puckering, and inter-ring bending modes collectively drive such relaxation dynamics. [ABSTRACT FROM AUTHOR]

Doubly resonant sum frequency generation (DR-SFG) serves as a potent characteristic technique for probing the electronic spectra and vibronic coupling of molecules on surfaces. In this study, we successfully developed a novel infrared (IR)–white light (WL) DR-SFG spectroscopy based on narrowband IR and tunable broadband WL. This novel method was employed to explore the excitation spectrum and vibronic couplings of sub-monolayer Rhodamine 6G molecules. Our findings elucidate that the xanthene skeleton vibrational modes exhibit strong coupling with the S0–S1 electronic transition. Notably, we observed not only the 0–0 transition of the S0–S1 electronic continuum but also the 0–1 transition, a first time observation in the realm of DR-SFG spectroscopy. This advanced DR-SFG spectroscopy methodology facilitates a more sensitive examination of electronic spectra and the coupling between electronic transitions and vibrational modes, heralding a significant advancement in the understanding of molecular interactions on surfaces. [ABSTRACT FROM AUTHOR]

In this article, we develop a vibronic theory of clocking in molecular quantum cellular automata (QCA). The clocking mechanism is considered for a trigonal trimeric mixed-valence (MV) system with one mobile electron, which is shown to act as the dimeric unit encoding binary information (Boolean states 0 or 1) coupled to a third redox center (Null state). The model includes the electron transfer between the three centers; vibronic coupling of the mobile charge with the "breathing" modes, forming a double degenerate Jahn–Teller vibration of the molecular triangle; and two electric fields, one collinear to the dimeric unit, which controls the binary states, and the other perpendicular to this unit, performing clocking. In the framework of the adiabatic approximation, the potential surface of the trimeric system has been studied and the condition determining switching and clocking has been analyzed in terms of the two controlling fields and the vibronic and transfer parameters. A thorough understanding of the site populations is achieved through the quantum-mechanical solution of the vibronic problem, maintaining the adiabatic condition for the controlling fields. It is shown that a MV trimer can act as a molecular clocked QCA cell, with favorable conditions being a positive electron transfer parameter and sufficiently strong vibronic coupling. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) is a very significant photophysical phenomenon and possesses potential applications. In this work, we try to give a rather detailed theoretical investigation of the SF process in the stacked polyacene dimer by combining the high-level quantum chemistry calculations and the quantum dynamics simulations based on the tensor network method. Starting with the construction of the linear vibronic coupling model, we explore the pure electronic dynamics and the vibronic dynamics in the SF processes. The role of vibrational modes in nonadiabatic dynamics is addressed. The results show that the super-exchange mechanism mediated by the charge-transfer state is found in both pure electronic dynamics and the nonadiabatic dynamics. Particularly the vibrational modes with the frequencies resonance with the adiabatic energy gap play very import roles in the SF dynamics. This work not only provides a deep and detailed understanding of the SF process but also verifies the efficiency of the tensor network method with the train structure that can serve as the reference dynamics method to explore the dynamics behaviors of complex systems. [ABSTRACT FROM AUTHOR]

Infrared spectra of C60+ and C120+, obtained via helium messenger spectroscopy, are reported. For C60+, new absorption features have been found just above the discrete vibrational spectrum of the ion. The absorption profile, which is broad and contains little structure, is assigned to one or more electronic absorption transitions and is in good agreement with predictions from time-dependent density functional theory. It seems likely that the transitions observed correspond to excitation from the 2A1u electronic ground state to one or both of the low-lying 2E1u and 2E2u electronic states previously identified as dark states of C60+. These states presumably become optically bright through vibronic coupling and specifically the Jahn–Teller effect. In the case of C120+, the simplest positively charged oligomer of C60, we present the first vibrational spectrum of this ion. Through a comparison with theory, vibrational features are best explained by a peanut-shaped structure for C120+, maintained by covalent bonding between the two C60 units. We have also discovered electronic transitions for C120+, which, similar to C60+, lie just above the vibrational spectrum. [ABSTRACT FROM AUTHOR]

Developing fluorescence-encoded infrared (FEIR) vibrational spectroscopy for single-molecule applications requires a detailed understanding of how the molecular response and external experimental parameters manifest in the detected signals. In Paper I [L. Whaley-Mayda, A. Guha, and A. Tokmakoff, J. Chem. Phys. 159, 194201 (2023)] we introduced a nonlinear response function theory to describe vibrational dynamics, vibronic coupling, and transition dipole orientation in FEIR experiments with ultrashort pulses. In this second paper, we apply the theory to investigate the role of intermode vibrational coherence, the orientation of vibrational and electronic transition dipoles, and the effects of finite pulse durations in experimental measurements. We focus on measurements at early encoding delays—where signal sizes are largest and therefore of most value for single-molecule experiments, but where many of these phenomena are most pronounced and can complicate the appearance of data. We compare experiments on coumarin dyes with finite-pulse response function simulations to explain the time-dependent behavior of FEIR spectra. The role of the orientational response is explored by analyzing polarization-dependent experiments and their ability to resolve relative dipole angles in the molecular frame. This work serves to demonstrate the molecular information content of FEIR experiments, and develop insight and guidelines for their interpretation. [ABSTRACT FROM AUTHOR]

Fluorescence-encoded infrared (FEIR) spectroscopy is an emerging technique for performing vibrational spectroscopy in solution with detection sensitivity down to single molecules. FEIR experiments use ultrashort pulses to excite a fluorescent molecule's vibrational and electronic transitions in a sequential, time-resolved manner, and are therefore sensitive to intervening vibrational dynamics on the ground state, vibronic coupling, and the relative orientation of vibrational and electronic transition dipole moments. This series of papers presents a theoretical treatment of FEIR spectroscopy that describes these phenomena and examines their manifestation in experimental data. This first paper develops a nonlinear response function description of Fourier-transform FEIR experiments for a two-level electronic system coupled to multiple vibrations, which is then applied to interpret experimental measurements in the second paper [L. Whaley-Mayda et al., J. Chem. Phys. 159, 194202 (2023)]. Vibrational coherence between pairs of modes produce oscillatory features that interfere with the vibrations' population response in a manner dependent on the relative signs of their respective Franck–Condon wavefunction overlaps, leading to time-dependent distortions in FEIR spectra. The orientational response of population and coherence contributions are analyzed and the ability of polarization-dependent experiments to extract relative transition dipole angles is discussed. Overall, this work presents a framework for understanding the full spectroscopic information content of FEIR measurements to aid data interpretation and inform optimal experimental design. [ABSTRACT FROM AUTHOR]

We report experimental differential cross sections (DCSs) for electron impact excitation of bands I to V of benzene at incident energies of 10, 12.5, 15, and 20 eV. They are compared to calculations using the Schwinger multichannel method while accounting for up to 437 open channels. For intermediate scattering angles, the calculations reveal that the most intense band (V) emerges from surprisingly similar contributions from all its underlying states (despite some preference for the dipole-allowed transitions). They further shed light on intricate multichannel couplings between the states of bands I to V and higher-lying Rydberg states. In turn, the measurements support a vibronic coupling mechanism for excitation of bands II and IV and also show an unexpected forward peak in the spin-forbidden transition accounting for band III. Overall, there is decent agreement between theory and experiment at intermediate angles and at lower energies and in terms of the relative DCSs of the five bands. Discrepancies between the present and previous experiment regarding bands IV and V draw attention to the need of additional experimental investigations. We also report measured DCSs for vibrational excitation of combined C–H stretching modes. [ABSTRACT FROM AUTHOR]

We report the experimental resonance enhanced multiphoton ionization spectrum of isoquinoline between 315 and 310 nm, along with correlated electronic structure calculations on the ground and excited states of this species. This spectral region spans the origin transitions to a π–π* excited state, which previous work has suggested to be vibronically coupled with a lower lying singlet n–π* state. Our computational results corroborate previous density functional theory calculations that predict the vertical excitation energy for the n–π* state to be higher than the π–π* state; however, we find an increase in the C–N–C angle brings the n–π* state below the energy of the π–π* state. The calculations find two out-of-plane vibrational modes of the n–π* state, which may be brought into near resonance with the π–π* state as the C–N–C bond angle increases. Therefore, the C–N–C bond angle may be important in activating vibronic coupling between the states. We fit the experimental rotational contour with a genetic algorithm to determine the excited state rotational constants and orientation of the transition dipole moment. The fits show a mostly in-plane polarized transition, and the projection of the transition dipole moment in the a-b plane is about 84° away from the a axis. These results are consistent with the prediction of our electronic structure calculations for the transition dipole moment of the π–π* excited state. [ABSTRACT FROM AUTHOR]

Organic chromophores such as the thionated derivatives of perylene diimides (PDIs) show prolonged triplet-excited state lifetimes in contrast to their pristine parent PDI molecule, which shows near unity fluorescence quantum yield. The excited state dynamics in the trans-dithionated PDI (S2-PDI) are studied here. Unlike PDI, the photo absorbing ππ* state of S2-PDI is in close proximity to quasi-degenerate nπ* states. The latter exhibits an interesting vibronic problem leading to the breaking of orbital symmetry mediated through non-totally symmetric vibrations. The time-dependent quantum dynamics are studied with a diabatic model Hamiltonian involving three singlet and three triplet states coupled via 22 vibrational modes. A combined effect of multiple internal-conversion and inter-system crossing (ISC) pathways leads to population transfer from the 1ππ* state to the 3ππ* state via the nπ* states, with an overall ISC rate of 0.70 ps that compares well with the experimental value. The calculated absorption spectra for PDI and S2-PDI reproduce the essential vibronic features in the observed experimental spectra. The dominant vibronic progressions are found to have significant contributions from the vinyl stretching modes of the PDI core. [ABSTRACT FROM AUTHOR]

Current-induced bond rupture is a fundamental process in nanoelectronic architectures, such as molecular junctions, and scanning tunneling microscopy measurements of molecules at surfaces. The understanding of the underlying mechanisms is important for the design of molecular junctions that are stable at higher bias voltages and is a prerequisite for further developments in the field of current-induced chemistry. In this work, we analyze the mechanisms of current-induced bond rupture employing a recently developed method, which combines the hierarchical equations of motion approach in twin space with the matrix product state formalism and allows accurate, fully quantum mechanical simulations of the complex bond rupture dynamics. Extending previous work [Ke et al. J. Chem. Phys. 154, 234702 (2021)], we consider specifically the effect of multiple electronic states and multiple vibrational modes. The results obtained for a series of models of increasing complexity show the importance of vibronic coupling between different electronic states of the charged molecule, which can enhance the dissociation rate at low bias voltages profoundly. [ABSTRACT FROM AUTHOR]

The oligomeric ruthenium‐based water oxidation catalyst, Ru(bda), is known to be experimentally anchored on graphitic surfaces through CH‐π stacking interactions between the auxiliary bda ([2,2′‐bipyridine]‐6,6′‐dicarboxylate) ligand bonded to ruthenium and the hexagonal rings of the surface. This anchoring provides control over their molecular coverage and enables efficient catalysis of water oxidation to dioxygen. The oligomeric nature of the molecule offers multiple anchoring sites at the surface, greatly enhancing the overall stability of the hybrid catalyst‐graphitic surface anode through dynamic bonding. However, the impact of this dynamic anchoring on the overall catalytic mechanism is still a topic of debate. In this study, a crucial proton‐coupled electron transfer event in the catalytic cycle is investigated using DFT‐based molecular dynamics simulations plus metadynamics. The CH‐π stacking anchoring plays a critical role not only in stabilizing this hybrid system but also in facilitating the proton‐coupled electron transfer event with possible vibronic couplings between the anchoring bonds motion and charge fluctuations at the catalyst – graphitic surface interface. Furthermore, this computational investigation displays the presence of a quartet spin state intermediate that can lead to the experimentally observed and thermodynamically more stable doublet spin state. [ABSTRACT FROM AUTHOR]

Porphyrins are a fundamental class of molecules involved in a multitude of biological and chemical functions ranging from photosynthesis in plants to biomarkers in medicine to optoelectronic devises. Despite the porphyrin molecule being such an important class of molecules known for centuries, its photophysics are surprisingly complex and models describing the spectroscopic behavior of porphyrins did not emerge until the 1950s. This review aims to distil the basics of porphyrin photophysics, describing how the Soret band and the Q band of the molecule are formed. In particular, a discussion of the four orbital theory and Hertzberg-Teller coupling will be conducted, both of which are necessary to understand the spectral properties of the porphyrin molecule. The review further aims to complement previous work discussing the chemical applications of hybrid light-matter states by discussing how the spectroscopic behavior of porphyrins is particularly useful in polariton chemistry. [ABSTRACT FROM AUTHOR]

The chemical synthesis of (CdSe)13 magic-sized clusters (MSCs) allows the replacement of host atoms by individual transition metals such as Mn. By analyzing the spectral fingerprints of the Mn2+ photoluminescence (PL) in MSCs with different dopant concentrations, we are able to distinguish between single Mn2+ ions and coupled Mn2+ pairs. In case of Mn2+ pair emission, temperature-dependent studies show a pronounced red shift, followed by a distinct blue shift of the PL energy upon heating. This is related to a spin ladder formation of the ground and excited states due to Mn2+–Mn2+ exchange interaction at cryogenic temperatures, which is assumed to vanish at higher temperatures. In contrast, single Mn2+ ion PL exhibits a unique redshift with increasing temperature, which can be attributed to a particularly strong coupling to vibronic modes due to the ultimate small size of the MSCs. [ABSTRACT FROM AUTHOR]

It has been well-established that the topography around conical intersections between excited electronic states is incorrectly described by coupled cluster and many other single reference theories (the intersections are "defective"). Despite this, we show both analytically and numerically that the geometric phase effect (GPE) is correctly reproduced upon traversing a path around a defective excited-state conical intersection (CI) in coupled cluster theory. The theoretical analysis is carried out by using a non-Hermitian generalization of the linear vibronic coupling approach. Interestingly, the approach qualitatively explains the characteristic (incorrect) shape of the defective CIs and CI seams. Moreover, the validity of the approach and the presence of the GPE indicate that defective CIs are local (and not global) artifacts. This implies that a sufficiently accurate coupled cluster method could predict nuclear dynamics, including geometric phase effects, as long as the nuclear wavepacket never gets too close to the conical intersections. [ABSTRACT FROM AUTHOR]

In purple bacteria, the fundamental charge-separation step that drives the conversion of radiation energy into chemical energy proceeds along one branch—the A branch—of a heterodimeric pigment–protein complex, the reaction center. Here, we use first principles time-dependent density functional theory (TDDFT) with an optimally-tuned range-separated hybrid functional to investigate the electronic and excited-state structure of the six primary pigments in the reaction center of Rhodobacter sphaeroides. By explicitly including amino-acid residues surrounding these six pigments in our TDDFT calculations, we systematically study the effect of the protein environment on energy and charge-transfer excitations. Our calculations show that a forward charge transfer into the A branch is significantly lower in energy than the first charge transfer into the B branch, in agreement with the unidirectional charge transfer observed experimentally. We further show that the inclusion of the protein environment redshifts this excitation significantly, allowing for energy transfer from the coupled Qx excitations. Through analysis of transition and difference densities, we demonstrate that most of the Q-band excitations are strongly delocalized over several pigments and that both their spatial delocalization and charge-transfer character determine how strongly affected they are by thermally-activated molecular vibrations. Our results suggest a mechanism for charge-transfer in this bacterial reaction center and pave the way for further first-principles investigations of the interplay between delocalized excited states, vibronic coupling, and the role of the protein environment in this and other complex light-harvesting systems. [ABSTRACT FROM AUTHOR]

Vibronic coupling is a critical mechanism in chemical reactions. However, its quantitative evaluation is challenging due to mathematical complexity and programming difficulty, and its experimental proof is often elusive due to overlap among neighboring states. Here, after exciting a vibrational level (ν = 0, 1, 2) of the intermediate N 1 s → π g * core-excited state in N2 molecules, we separate the resonant Auger decay channels that lead to the lowest dissociation limit in the two-dimensional energy correlation maps. From three kinetic energy release spectra of these channels at different vibrational quantum numbers, we give the first experimental proof of the vibronic coupling between two resonant Auger final states 12Πg and 22Πg. [ABSTRACT FROM AUTHOR]

We report a joint experimental and computational study of the photoelectron spectroscopy and the dissociative photoionization of fulminic acid, HCNO. The molecule is of interest to astrochemistry and astrobiology as a potential precursor of prebiotic molecules. Synchrotron radiation was used as the photon source. Dispersive photoelectron spectra were recorded from 10 to 22 eV, covering four band systems in the HCNO cation, and an ionization energy of 10.83 eV was determined. Transitions into the Renner–Teller distorted X+2Π state of the cation were simulated using wavepacket dynamics based on a vibronic coupling Hamiltonian. Very good agreement between experiment and theory is obtained. While the first excited state of the cation shows only a broad and unstructured spectrum, the next two higher states exhibit a well-resolved vibrational progression. Transitions into the excited electronic states of HCNO+ were not simulated due to the large number of electronic states that contribute to these transitions. Nevertheless, a qualitative assignment is given, based on the character of the orbitals involved in the transitions. The dissociative photoionization was investigated by photoelectron–photoion coincidence spectroscopy. The breakdown diagram shows evidence for isomerization from HCNO+ to HNCO+ on the cationic potential energy surface. Zero Kelvin appearance energies for the daughter ions HCO+ and NCO+ have been derived. [ABSTRACT FROM AUTHOR]

A synchrotron-based photoionization spectrum up to 27 eV represents a considerable improvement in resolution over early He(I) and He(II) spectra. Symmetry-adapted coupled cluster calculations of the ionic state sequence give the sequence of state vertical ionization energies (VIE) as 12B2 < 12B1 < 12A2 < 22B1 < 12A1. Generally, these symmetry-adapted cluster configuration interactions VIE match reasonably well with the experimental spectrum over this wide energy range. Density functional calculations of the corresponding adiabatic terms (AIE) were also performed. Higher energy ionic states were determined by complete active space self-consistent field methods; these include all π-ionizations and some σ-ionic states. These were analyzed by Franck–Condon (FC) procedures and compared with an experiment. The spectral onset is complex, where two states, later shown to be the 12B2 and 12B1 states, are strongly overlapping. The superposition of the FC vibrational structure in the 12B2 and 12B1 states accounts for most of the peaks arising at the onset of the photoelectron spectra. However, the small separation between these two ionic states makes vibronic interaction fairly inevitable. In the absence of Herzberg–Teller analyses for ionic states, we have sought and determined a transition state between the 12B2 and 12B1 states, showing that vibronic coupling does occur. The lack of degradation in the vibrational envelope of the higher of the two states contrasts with our previous work on the halogenobenzenes, where overlapping state envelopes led to considerable widening of the line width at half-height of the higher energy states. [ABSTRACT FROM AUTHOR]

Low‐dimensional metal halides (LDMHs) represent a promising class of materials in various luminescent applications because of their self‐trapped exciton (STE) emissions with unique properties such as broad luminescence spectra, large Stokes shift, and high color rendition. LDMHs at the molecular level can be constructed, including 2D layers, 1D chains, and 0D clusters assembled by polyhedra units, all of which exhibit significantly different luminescence properties from 3D MHs. The dimensional regulation of LDMHs has been explored for years, including the choice of organic cations, modulating electron‐phonon coupling effect, and adding external temperature and pressure. Herein, this review discusses the synergy between structural engineering and solvent effects for LDMHs, including the emission mechanisms for LDMHs and the roles solvent molecules play in regulating the dimensions. In addition, challenges and opportunities for LDMHs are discussed to shed light on the future development of novel materials with multifunctional optical properties suitable for practical applications. [ABSTRACT FROM AUTHOR]

The electronic structure and photophysical properties of several acrylaldehyde‐bridged deazaflavin derivatives (cFLs) were investigated theoretically. The impact of acrylaldehyde bridging on photophysical properties of deazaflavin (cFL) is strongly site‐dependent. Specifically, the change of adiabatic energy of electronic transitions(ΔEad) and vibronic coupling promote fluorescent emission to be comparable to internal conversion of cFL and cFL4 (both C5−C6 and C9−N10 bridged, but C9−N10 bridged by propene), turning them eligible as fluorescent sensors. As El‐Sayed's rule is satisfied in cFL1(C5−C6 bridged), cFL2(C9−N10 bridged) and cFL3(both C5−C6 and C9−N10 bridged), intersystem crossing from first singlet excited state to triplet excited states (Tn) become dominant and the evolution of excited cFLs from T1 appears vital. The rate constants of photophysical processes indicate these cFLs are of dominantly high steady state T1 concentration and are potential triplet sensitizers. We expect the findings would pave the way for rational design of novel cFLs with extraordinary photophysical properties. [ABSTRACT FROM AUTHOR]

Summary: Fast battery charging units act as non‐linear loads, which induce a more harmonic effect in the utility grid. Hence, maintaining the stable voltage, current ripple, and total harmonic distortions within the permissible IEEE std level during the charging time of grid to electric vehicle (G2V) has become an important task for researchers in the future. In order to mitigate power fluctuations during every charging cycle, it will enhance the battery life cycle in electric vehicles (EVs). Three phase–three level–three switch Vienna rectifier with fuzzy logic controller tuned PID controller is used here for AC/DC conversion with minimum switching loss. A fuzzy intelligent control strategy has been employed with the DC link voltage regulator in order to sustain the DC link voltage as constant and progress the voltage/current profile by injecting active power at the point of common coupling. Unit vector template (UVT)‐based control strategy is employed here to identify the fundamental components from the load side and also estimate the reference phase current. This scheme enhances the performance and reduces the mathematical system complexity to diminish the harmonics in the distribution grid. The adaptability and feasibility of this proposed control method have been verified by the MATLAB simulation tool. To validate the response of the Vienna Rectifier with UVT controller are simulated with different unbalanced load conditions and also verified with 30 kW laboratory prototype experimental results using dsPIC30F4011 controller and the switch is IRFP260 with power diode RHRG30120. [ABSTRACT FROM AUTHOR]

A reaction center is a unique biological system that performs the initial charge separation within a Photosystem II (PSII) multiunit enzyme, which eventually drives the catalytic water-splitting in plants and algae. The possible role of quantum coherences coinciding with the energy and charge transfer processes in PSII reaction center is one of the active areas of research. Here, we study these quantum coherences by using a numerically exact method on an excitonic dimer model, including linear vibronic coupling and employing optimal parameters from experimental two-dimensional coherent spectroscopic measurements. This enables us to precisely capture the excitonic interaction between pigments and the dissipation of the energy from electronic and charge-transfer (CT) states to the protein environment. We employ the time nonlocal (TNL) quantum master equation to calculate the population dynamics, which yields numerically reliable results. The calculated results show that, due to the strong dissipation, the lifetime of electronic coherence is too short to have direct participation in the charge transfer processes. However, there are long-lived vibrational coherences present in the system at frequencies close to the excitionic energy gap. These are strongly coupled with the electronic coherences, which makes the detection of the electronic coherences with conventional techniques very challenging. Additionally, we unravel the strong excitonic interaction of radical pair ( P D 1 and P D 2 ) in the reaction center, which results in a long-lived electronic coherence of >100 fs, even at room temperature. Our work provide important physical insight to the charge separation process in PSII reaction center, which may be helpful for better understanding of photophysical processes in other natural and artificial light-harvesting systems. [ABSTRACT FROM AUTHOR]

It remains unclear how the collective strong coupling of cavity-confined photons to the electronic transitions of molecular chromophore leverages the distinct properties of the polaritonic constituents for future technologies. In this study, we design, fabricate, and characterize multiple types of Fabry-Pérot (FP) mirco-resonators containing copper(II) tetraphenyl porphyrin (CuTPP) to show how cavity polariton formation affects radiative relaxation processes in the presence of substantial non-Condon vibronic coupling between two of this molecule's excited electronic states. Unlike the prototypical enhancement of Q state radiative relaxation of CuTPP in a FP resonator incapable of forming polaritons, we find the light emission processes in multimode cavity polariton samples become enhanced for cavity-exciton energy differences near those of vibrations known to mediate non-Condon vibronic coupling. We propose the value of this detuning is consistent with radiative relaxation of Herzberg-Teller polaritons into collective molecular states coupled to the cavity photon coherently. We contrast the feature stemming from light emission from the HT polariton state with those that occur due to polariton-enhanced light absorption. Our results demonstrate the landscape of molecular and photonic interactions enabled by cavity polariton formation using complex chromophores and how researchers can design resonators to leverage these interactions to characterize and control polaritonic properties. [ABSTRACT FROM AUTHOR]

The circularly polarized luminescence (CPL) spectra of S‐ and X‐shaped double helicenes exhibit distinct vibrational structures and overall shape variations. In this study, we conducted an in‐depth investigation into the vibronic effects influencing the CPL spectra of two double helicenes, namely DPC and DNH. Employing state‐of‐the‐art computations utilizing the FC‐HT1|VH model at the CAM−B3LYP/def2‐TZVP level, we unveiled the paramount impact of Franck–Condon (FC), Herzberg‐Teller (HT), and Duschinsky effects on their chiroptical responses. Our research underscores the pivotal role of structural deformations associated with the S1‐to‐S0 electronic transition in molding CPL spectra and wavelength‐dependent dissymmetry (g) factor values, as well as the significance of HT effects in shaping and enhancing CPL responses. This extensive investigation not only advances our comprehension of the vibronic characteristics in configurationally distinct double helicenes but also offers valuable insights for the design of chiral molecules featuring controllable or finely‐tunable CPL responses. [ABSTRACT FROM AUTHOR]

The E ⊗ e Jahn–Teller (JT) effects associated with the lowest excited degenerate electronic states (S 1 and S 2 ) of [6]-, [8]- and [10]cycloparaphenylene dications are studied to unravel their size-dependent optical properties. A model Hamiltonian within the linear vibronic coupling approach is adapted to generate the JT-split potential energy surfaces. Computed JT stabilization energy follows the trend: [6]CPP 2 + < [8]CPP 2 + > [10]CPP 2 + . Theoretical absorption spectral features are generated using the wavepacket simulations within the reduced- and full-dimensional framework. These simulations reproduce the size-dependent absorption spectral broadening where the broadening increases with the increase in CPP ring size. The near-degeneracy of JT-split states (S 1 and S 2 ) indicates a possible fluorescence emission from both the states in these molecules. [ABSTRACT FROM AUTHOR]

The electronic and vibrational structures of 1,2-benzanthracene-h12 (aBA-h12) and 1,2-benzanthracene-d12 (aBA-d12) were elucidated by analyzing fluorescence excitation spectra and dispersed fluorescence spectra in a supersonic jet on the basis of DFT calculation. We also observed the high-resolution and high-precision fluorescence excitation spectrum of the S 1 ← S 0 0 0 0 band, and determined the accurate rotational constants in the zero-vibrational levels of the S0 and S1 states. In this high-resolution measurement, we used a single-mode UV laser whose frequencies were controlled with reference to an optical frequency comb. The inertial defect is negligibly small, the molecule is considered to be planar, and the obtained rotational constants were well reproduced by the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculation. Both a-type and b-type transitions are found to be included in the rotationally resolved spectrum, and the a-type contribution is dominant, that is, the transition moment is nearly parallel to the long axis of the aBA molecule. We concluded that the S1 state is mainly composed of the Φ(B) configuration. The observed fluorescence lifetime (106 ns) is considerably longer than that of the Φ(A) system, such as anthracene (18 ns). The transition moment for the lower state of mixed states becomes small, reflecting a near-cancelation of the contributions from the parts of the wavefunction corresponding to the two electronic configurations. The bandwidth of the S2 ← S0 transition is large, and the structure is complicated. It is attributed to vibronic coupling with the high vibrational levels of the S1 state. [ABSTRACT FROM AUTHOR]

A detailed insight behind the structure of absorption bands of the photochromic couple dimethyldihydropyrene (DHP)/metacyclophanediene (CPD) is studied employing vibronic coupling theory. Two separate model molecular Hamiltonians, including a maximum of four electronic states and 18 vibrational modes for DHP and five electronic states and 20 vibrational modes for CPD, are constructed in a diabatic electronic representation. The parameters of the Hamiltonians are estimated from the electronic energies obtained from extensive density functional theory (DFT) and time-dependent DFT calculations. Based on these Hamiltonians' parameters, a detailed analysis of potential energy curves is performed in conjunction with positional and energetic locations of several stationary points in multi-dimensional potential energy surfaces. Based on the results of electronic structure calculations, quantum nuclear dynamics studies on the electronic excited states of DHP and CPD are performed to understand the impact of non-adiabatic effects on the formation of vibronic structures of absorption bands of these photo-isomers. [ABSTRACT FROM AUTHOR]

Vibronic coupling in the first eight electronic excited states of Pentafluorobenzene (PFBz) is investigated in this article. In particular, the vibronic coupling between the optically bright ππ* and optically dark πσ* states of PFBz is considered. A model 8 × 8 diabatic Hamiltonian is constructed in terms of normal coordinate of vibrational modes using the standard vibronic coupling theory and symmetry selection rule. The Hamiltonian parameters are estimated with the aid of extensive ab initio quantum chemistry calculations. The topography of the first eight electronic excited states of PFBz is examined at length, and multiple multi-state conical intersections are established. The nuclear dynamics calculations on the coupled electronic surfaces are carried out from first principles by the wave packet propagation method. Theoretical results are found to be in good accord with the available experimental optical absorption spectrum of PFBz. [ABSTRACT FROM AUTHOR]

Vibronic interactions in the ground and two excited states of the imidazole radical cation, X2A″ (π−1), A2A′ (nσ−1), and B2A″ (π−1), and the associated nuclear dynamics were studied theoretically. The results were used to interpret the recent photoelectron measurements [M. Patanen et al., J. Chem. Phys. 155, 054304 (2021)]. The present high-level electronic structure calculations employing, in particular, the single, double, and triple excitations and equation-of-motion coupled-cluster method accounting for single and double excitation approaches and complete basis set extrapolation technique for the evaluation of the vertical ionization energies of imidazole indicate that the A 2A′ and B 2A″ states are very close in energy and subject to non-adiabatic effects. Our modeling confirms the existence of pronounced vibronic coupling of the A 2A′ and B 2A″ states. Moreover, despite the large energy gap of nearly 1.3 eV, the ground state X 2A″ is efficiently coupled to the A 2A′ state. The modeling was performed within the framework of the three-state linear vibronic coupling problem employing Hamiltonians expressed in a basis of diabatic electronic states and parameters derived from ab initio calculations. The ionization spectrum was computed using the multi-configuration time-dependent Hartree method. The calculated spectrum is in good agreement with the experimental data, allowing for some interpretation of the observed features to be proposed. [ABSTRACT FROM AUTHOR]

A model designed to mimic the implications of the collective optical response of molecular ensembles in optical cavities on molecular vibronic dynamics is investigated. Strong molecule–radiation field coupling is often reached when a large number N of molecules respond collectively to the radiation field. In electronic strong coupling, molecular nuclear dynamics following polariton excitation reflects (a) the timescale separation between the fast electronic and photonic dynamics and the slow nuclear motion on one hand and (b) the interplay between the collective nature of the molecule–field coupling and the local nature of the molecules nuclear response on the other. The first implies that the electronic excitation takes place, in the spirit of the Born approximation, at an approximately fixed nuclear configuration. The second can be rephrased as the intriguing question of whether the collective nature of optical excitation leads to collective nuclear motion following polariton formation resulting in so-called polaron decoupled dynamics. We address this issue by studying the dynamical properties of a simplified Holstein–Tavis–Cummings-type model, in which boson modes representing molecular vibrations are replaced by two-level systems, while the boson frequency and the vibronic coupling are represented by the coupling between these levels (that induces Rabi oscillations between them) and electronic state dependence of this coupling. We investigate the short-time behavior of this model following polariton excitation as well as its response to CW driving and its density of states spectrum. We find that, while some aspects of the dynamical behavior appear to adhere to the polaron decoupling picture, the observed dynamics mostly reflect the local nature of the nuclear configuration of the electronic polariton rather than this picture. [ABSTRACT FROM AUTHOR]

Strong Coulomb repulsion between the two charges in a square planar mixed-valence cell in quantum cellular automata (QCA) allows us to encode the binary information in the two energetically beneficial diagonal distributions of the electronic density. In this article, we pose a question: to what extent is this condition obligatory for the design of the molecular cell? To answer this question, we examine the ability to use a square-planar cell composed of one-electron mixed valence dimers to function in QCA in a general case when the intracell Coulomb interaction U is not supposed to be extremely strong, which means that it is comparable with the characteristic electron transfer energy (violated strong U limit). Using the two-mode vibronic model treated within the semiclassical (adiabatic) and quantum-mechanical approaches, we demonstrate that strong vibronic coupling is able to create a considerable barrier between the two diagonal-type charge configurations, thus ensuring bistability and polarizability of the cells even if the Coulomb barrier is not sufficient. The cases of weak and moderate Coulomb repulsion and strong vibronic coupling are exemplified by consideration of the cation radicals of the two polycyclic derivatives of norbornadiene [C12H12]+ and [C17H16]+ with the terminal C=C chromophores playing the role of redox sites. By using the detailed ab initio data, we reveal the main characteristics of the bi-dimeric cells composed of these molecules and illustrate the pronounced effect of the vibronic recovery clearly manifesting itself in the shape of the cell–cell response function. Revealing such "vibronic recovery" of strong localization when the strong U limit is violated suggests a way to a significant expansion of the class of molecular systems suitable as QCA cells. [ABSTRACT FROM AUTHOR]

Heavy element compounds with high symmetries often feature both spin–orbit coupling and vibronic coupling. This is especially true for systems with tetrahedral and octahedral symmetries, whose electronic states may be threefold degenerate and experience complicated Jahn–Teller and pseudo-Jahn–Teller interactions. To accurately describe these interactions, high quality spin–orbit vibronic Hamiltonian operators are needed. In this study, we present a unified one-electron Hamiltonian formalism for spin–orbit vibronic interactions for systems in all tetrahedral and octahedral symmetries. The formalism covers all spin–orbit Jahn–Teller and pseudo-Jahn–Teller problems in the symmetries with arbitrary types and arbitrary numbers of vibrational modes and generates Hamiltonian expansion formulas of arbitrarily high order. [ABSTRACT FROM AUTHOR]

Hyper-Raman (HR) spectra of benzene-h6, benzene-d6, and pyridine in the liquid phase excited at 1064 nm were measured by a picosecond laser with a high repetition rate. Although benzene and pyridine are important aromatic molecules, the qualities of the HR spectra previously reported were not high enough to be compared with those of IR and Raman spectroscopy. Our HR spectroscopic system significantly improves sensitivity that enables the detection of HR bands of benzene and pyridine not observed before. In addition to band assignments, we interpret HR bands of benzene based on the vibronic coupling theory of (pre-) resonance hyper-Raman scattering. Depolarization ratios of HR bands of benzene and pyridine, obtained from polarized-HR measurements, are first examined from a theoretical point of view of HR spectroscopy. Moreover, we evaluate quantum chemical calculations for HR spectra by comparing experimental and computational spectra. We show that the frequency-dependent polarizability and hyperpolarizability calculations using time-dependent density functional theory well reproduce the HR experiments for bulk aromatic compounds. [ABSTRACT FROM AUTHOR]

High-resolution velocity-map imaged photoelectron spectra of the ethynyl anions C2H− and C2D− are measured at photon wavelengths between 355 and 266 nm to investigate the complex interactions between the closely lying X ̃ 2 Σ + and A ̃ 2 Π electronic states. An indicative kinetic energy resolution of 0.4%, together with the full angular dependence of the fast electrons, provides a detailed description of the vibronically coupled structure. It is demonstrated that a modest quadratic vibronic coupling model, parameterized by the quasidiabatic ansatz, is sufficient to accurately recreate all the observed vibronic interactions. Simulated spectra are shown to be in excellent agreement with the experimental data, verifying the proposed model and providing a framework that may be used to accurately simulate spectra of larger C2nH monohydride carbon chains. New spectral assignments are supported by experimental electron anisotropy measurements and Dyson orbital calculations. [ABSTRACT FROM AUTHOR]

Long-wavelength, near-infrared small-molecule dyes are attractive in biophotonics. Conventionally, they rely on expanded aromatic structures for redshift, which comes at the cost of application performance such as photostability, cell permeability, and functionality. Here, we report a ground-state antiaromatic strategy and showcase the concise synthesis of 14 cationic aminofluorene dyes with mini structures (molecular weights: 299–504 Da) and distinct spectra covering 700–1600 nm. Aminofluorene dyes are cell-permeable and achieve rapid renal clearance via a simple 44 Da carboxylation. This accelerates optical diagnostics of renal injury by 50 min compared to existing macromolecular approaches. We develop a compact molecular sensing platform for in vivo intracellular sensing, and demonstrate the versatile applications of these dyes in multispectral fluorescence and optoacoustic imaging. We find that aromaticity reversal upon electronic excitation, as indicated by magnetic descriptors, not only reduces the energy bandgap but also induces strong vibronic coupling, resulting in ultrafast excited-state dynamics and unparalleled photostability. These results support the argument for ground-state antiaromaticity as a useful design rule of dye development, enabling performances essential for modern biophotonics. Near-infrared small molecule dyes are attractive in biophotonics, but generally rely on expanded aromatic structures to achieve this redshift. Here the authors report the use of a ground state antiaromatic strategy for 14 aminofluorene dyes, and their use in imaging kidney injury. [ABSTRACT FROM AUTHOR]

Tokamak fusion reactors produce energetic He ions that penetrate surfaces less than 20 μm and neutrons that spread throughout the reactor. Experiments with similar swift He ions in heavy metals show that the vibronic coupling of nonlinear lattice excitations creates mobile lattice excitations, called quodons. These are decoupled from phonons, move ballistically at near sonic speed, and propagate easily in metals and insulators. They can couple to and transport electric charge, which allows their observation in experiments. They rapidly disperse heat throughout a fusion reactor and carry charge through electrical insulators. In this article, an experimental design is presented that separates quodon current and conduction current and therefore makes it possible to measure the former. Also, the time‐of‐flight experiments are presented that lead to an estimation of quodon speed which is of the order of the sound velocity and therefore much faster than the drift of electrons or holes in conduction currents. Herein, results are presented on quodon current in tungsten, a material widely used in nuclear fusion technology, showing that many quodons are produced in fusion reactors. It is predicted that at high output powers, quodons created by He ions and neutrons may adversely impact on cryogenic systems. [ABSTRACT FROM AUTHOR]

We present a high-resolution study on the B2Π-X2Π electronic origin band spectrum of the C6H radical with its center at ~18990 cm-1 The C6H radicals are produced in a pulsed supersonic slit-jet discharge source and detected in direct absorption by sensitive cavity ring-down spectroscopy. By using a home-made narrow linewidth nanosecond pulsed laser source, the experimental spectrum allows to resolve the ∧-type doublet fine structures in high-J rotational lines. A set of improved B2Π state constants, including the ∧-type doubling parameters of p′ = −1.16(9)x10−3 cm−1q′ = -1.22(7)x10−4 cm−1 are determined from analysis of the experimental spectrum. An analysis on the spectral line profile has resulted in a significant linewidth broadening of ~0.05±0.01 cm−1, corresponding to a B2Π state lifetime of ~100±20 ps. The short lifetime of the excited B2Π state is proposed due to fast internal vibronic couplings to high-lying vibronic levels of lower electronic states. [ABSTRACT FROM AUTHOR]

4,4‐Difluoro‐4‐borata‐3a‐azonia‐4a‐aza‐s‐indacene (BODIPY) dyes are extensively used in various applications of their triplet states, ranging from photoredox catalysis, through triplet sensitization to photodynamic therapy. However, the rational design of BODIPY triplet chromophores by ab initio modelling is limited by their strong interactions of spin, electronic and vibrational dynamics. In particular, spin‐vibronic coupling is often overlooked when estimating intersystem crossing (ISC) rates. In this study, a combined experimental and theoretical approach using spin‐vibronic coupling to correctly describe ISC in BODIPY dyes was developed. For this purpose, seven π‐extended BODIPY derivatives with iodine atoms in different positions were examined. It was found that the heavy‐atom effect of iodine atoms is site specific, causing high triplet yields in only some positions. This site‐specific ISC was explained by El‐Sayed rules, so both the contribution and character of the molecular orbitals involved in the excitation must be considered when predicting the ISC rates. Overall, the rational design of BODIPY triplet chromophores requires using (i) the high‐quality electronic structure theory, including both static and dynamical correlations; and (ii) the two‐component wave function Hamiltonian, and rationalizing; and (iii) ISC based on the character of the molecular orbitals of heavy atoms involved in the excitation, expanding El‐Sayed rules beyond their traditional applications. [ABSTRACT FROM AUTHOR]

The contemporary paper refers back to the instability of linear in GeX2 (X=F, Cl & Br) molecules because of the vibronic coupling effect. Optimization and the following frequency calculations in those molecules found out that every one of those molecules were unstable in high symmetry linear (with D∞h symmetry) geometry and their systems have been bent to lower C2v symmetry geometry. On this work, we've used, TD-DFT (B3LYP/6-31G (d) calculations to gain the strength curves of the ground and excited in the bending directions Q (πu) of compounds 1-3. The vibronic coupling interaction between 1∑g+ ground and the first 1∑u excited states in the Q (∑u) direction via (1∑g+ + 1πu) ⊗ πu PJTE problem was the reason for the symmetry breaking phenomenon. Additionally, changing atoms with different elements together with the electronegative exchange and the degree of overlap at once have an effect on the pattern of molecular orbitals. The NBO calculations were carried out to define a stability measure through the stabilization energy, E2 parameter. According to the consequences received from the vibronic principle of PJT, the bent shape of those analogs is the result of LP(3) X → LP*(2)Ge1 electron delocalization .The PJT stabilization strength decreases from compound 1 to compound three. Moreover, by the decrease of the energy gaps between reference states (Δ) the primary force constant of the ground state in the Q (πu) direction (K0) could decrease from compound 1 to compound 3. [ABSTRACT FROM AUTHOR]

Application of the time-dependent variational principle to a linear combination of frozen-width Gaussians describing the nuclear wavefunction provides a formalism where the total energy is conserved. The computational downside of this formalism is that trajectories of individual Gaussians are solutions of a coupled system of differential equations, limiting implementation to serial propagation algorithms. To allow for parallelization and acceleration of the computation, independent trajectories based on simplified equations of motion were suggested. Unfortunately, within practical realizations involving finite Gaussian bases, this simplification leads to breaking the energy conservation. We offer a solution for this problem by using Lagrange multipliers to ensure the energy and norm conservation regardless of basis function trajectories or basis completeness. We illustrate our approach within the multi-configurational Ehrenfest method considering a linear vibronic coupling model. [ABSTRACT FROM AUTHOR]