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Different hydrogen bonding environments of the retinal protonated Schiff base control the photoisomerization in channelrhodopsin-2
摘要： The first event of the channelrhodopsin-2 (ChR2) photocycle, i.e. trans-to-cis photoisomerization, is studied by means of quantum mechanics/molecular mechanics, taking into account the flexible retinal environment in the ground state. By treating the chromophore at the ab initio multiconfigurational level of theory, we can rationalize the experimental findings based on pump–probe spectroscopy, explaining the different and more complex scenario found for ChR2 in comparison to other rhodopsins. In particular, we find that depending on the hydrogen bonding pattern, different excited states are involved, hence making it possible to suggest one pattern as the most productive. Moreover, after photoisomerization the structure of the first photocycle intermediate, P500, is characterized by simulating the infrared spectrum and compared to available experimental data. This was obtained by extensive molecular dynamics, where the chromophore is described by a semi-empirical method based on density functional theory. The results clearly identify which counterion is responsible for accepting the proton from the retinal Schiff base: the side chain of the glutamic acid E123.
关键词： FTIR spectroscopy,quantum mechanics/molecular mechanics,retinal Schiff base,photoisomerization,channelrhodopsin-2,hydrogen bonding,excited states,molecular dynamics
更新于2025-09-19 17:15:36
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Theoretical study of the excited state properties of luminescent phospholes
摘要： TD-DFT calculations with the use of hybrid PBE0 functional and def-TZVP Alrich’s basis set are shown to provide an excellent cost-effective computational approach for the treatment of the excited states of phospholes. The general geometrical changes taking place upon excitation and bearing a common character in the series of considered phospholes have been revealed. It is demonstrated that conjugation of P-heterol with exocyclic aryl fragments makes the main impact on the ground-state (electronic absorption) properties of phospholes. The main structural transformations of the excited states responsible for emission properties are shown to occur mostly inside the P-hetorole ring causing change in bonds ordering upon excitation. The general good agreement between the experiments and the calculations found for the considered systems suggests that the applied theoretical approach can be used as an effective predictive tool for the rational design of luminescent phospholes.
关键词： phospholes,excited states properties,TD-DFT,UV-vis absorption/emission
更新于2025-09-19 17:15:36
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Highly efficient blue organic light-emitting diodes based on carbene-metal-amides
摘要： Carbene-metal-amides are soluble and thermally stable materials which have recently emerged as emitters in high-performance organic light-emitting diodes. Here we synthesise carbene-metal-amide photoemitters with CF3-substituted ligands to show sky-blue to deep-blue photoluminescence from charge-transfer excited states. We demonstrate that the emission colour can be adjusted from blue to yellow and observe that the relative energies of charge transfer and locally excited triplet states influence the performance of the deep-blue emission. High thermal stability and insensitivity to aggregation-induced luminescence quenching allow us to fabricate organic light-emitting diodes in both host-free and host-guest architectures. We report blue devices with a peak external quantum efficiency of 17.3% in a host-free emitting layer and 20.9% in a polar host. Our findings inform the molecular design of the next generation of stable blue carbene-metal-amide emitters.
关键词： charge-transfer excited states,photoluminescence,carbene-metal-amides,organic light-emitting diodes,external quantum efficiency
更新于2025-09-19 17:13:59
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Single‐reference coupled cluster methods for computing excitation energies in large molecules: The efficiency and accuracy of approximations
摘要： While methodological developments in the last decade made it possible to compute coupled cluster (CC) energies including excitations up to a perturbative triples correction for molecules containing several hundred atoms, a similar breakthrough has not yet been reported for excited state computations. Accurate CC methods for excited states are still expensive, although some promising candidates for an efficient and accurate excited state CC method have emerged recently. This review examines the various approximation schemes with particular emphasis on their performance for excitation energies and summarizes the best state-of-the-art results which may pave the way for a robust excited state method applicable to molecules of hundreds of atoms. Among these, special attention will be given to exploiting the techniques of similarity transformation, perturbative approximations as well as integral decomposition, local and embedding techniques within the equation of motion CC framework.
关键词： single reference,coupled cluster,efficiency,excited states,accuracy
更新于2025-09-19 17:13:59
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Phonon-Mediated and Weakly Size-Dependent Electron and Hole Cooling in CsPbBr <sub/>3</sub> Nanocrystals Revealed by Atomistic Simulations and Ultrafast Spectroscopy
摘要： We combine state-of-the-art ultrafast photoluminescence and absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate charge-carrier cooling in CsPbBr3 nanocrystals over a very broad size regime, from 0.8 nm to 12 nm. Contrary to the prevailing notion that polaron formation slows down charge-carrier cooling in lead-halide perovskites, no suppression of carrier cooling is observed in CsPbBr3 nanocrystals except for a slow cooling (over ~ 10 ps) of ‘warm’ electrons in the vicinity (within ~ 0.1 eV) of the conduction band edge. At higher excess energies, electrons and holes cool with similar rates, on the order of 1 eV ps-1 carrier-1 and increasing weakly with size. Our ab initio simulations suggest that cooling proceeds via fast phonon-mediated intra-band transitions driven by strong and size-dependent electron-phonon coupling. The presented experimental and computational methods yield the spectrum of involved phonons and may guide the development of devices utilizing hot charge carriers.
关键词： electron-phonon coupling,hot carriers,nonadiabatic molecular dynamics,Charge-carrier cooling,lead-halide perovskite nanocrystal,excited-states dynamics
更新于2025-09-19 17:13:59
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A Projective Method for the Calculation of Excited State Electronic Coupling: Isolating Charge Transfer/Recombination Processes in Organic Photovoltaics
摘要： Electronic coupling between excited states is a vital parameter required in order to describe the ultrafast energy and charge transfer processes that occur in photo-responsive organic materials. In such systems short-range Coulombic, exchange, overlap, and configuration interaction effects must all be accounted for. Although a number of methods are available, the evaluation of the coupling between arbitrary excited states remains challenging. In this contribution, a flexible and scalable method for the calculation of short-range electronic coupling between excited states is developed. Excitation- or charge-localized states are projected onto the adiabatic states of a dimeric molecular system using an efficient wavefunction overlap algorithm. In addition to correctly treating Coulombic, exchange and overlap interactions, the inclusion of multistate interactions is inherent in the procedure. The method is then used to disentangle excitation energy transfer, charge-transfer, and charge recombination processes in donor acceptor systems relevant to organic photovoltaics, with a view towards the development of material design principles. Calculations were performed within single-excitation frameworks, but the scheme has the potential to be extended to multireference/higher-order excitation quantum-chemical methods.
关键词： excitation energy transfer,excited states,electronic coupling,charge transfer,organic photovoltaics
更新于2025-09-16 10:30:52
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Nonlinear optics at excited states of exciton polaritons in two-dimensional atomic crystals
摘要： Exciton polaritons (EP) are partial-light partial-matter quasiparticles in semiconductors demonstrating striking quantum phenomena such as Bose-Einstein condensation and single-photon nonlinearity. In these phenomena, the governing process is the EP relaxation into the ground states upon excitation, where various mechanisms are extensively investigated with thermodynamic limits. However, the relaxation process becomes drastically different and could significantly advance the understanding of EP dynamics for these quantum phenomena, when excited states of EP are involved. Here, for the first time, we observe nonlinear optical responses at the EP excited states in a monolayer tungsten disulphide (WS2) microcavity, including dark excited states and dynamically metastable upper polariton band. The nonlinear optics leads to unique emissions of ground states with prominent valley degree of freedom (DOF) via anomalous relaxation process, which is applicable to a wide range of semiconductors from monolayer transition metal dichalcogenides (TMDs) to emerging halide perovskites. This work promises possible approaches to challenging experiments such as valley polariton condensation. Moreover, it also constructs a valley-dependent solid state three-level system for terahertz photonics and stimulated Raman adiabatic passage.
关键词： excited states,exciton-polaritons,relaxation dynamics,Nonlinear optics,monolayer transition metal dichalcogenide
更新于2025-09-16 10:30:52
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Lanczos-based equation-of-motion coupled-cluster singles-and-doubles approach to the total photoionization cross section of valence excited states
摘要： Excitation energies and oscillator strengths of the first two electronically excited states of helium, water, sulfur dioxide, molecular nitrogen, and carbon monoxide were obtained from an asymmetric-Lanczos-based formulation of the equation-of-motion coupled cluster singles and doubles approach. The total photoionization cross sections were generated by two different methodologies: an analytic continuation procedure based on the Padé approximants and the Stieltjes imaging technique. The results are compared with theoretical photoionization cross sections from algebraic diagrammatic construction [ADC(2)] and ADC(2)-x calculations [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] and with available experimental data.
关键词： Stieltjes imaging technique,coupled-cluster singles-and-doubles,photoionization cross section,Lanczos-based equation-of-motion,valence excited states,Padé approximants
更新于2025-09-12 10:27:22
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Enhanced triplet state generation through radical pair intermediates in BODIPY-quantum dot complexes
摘要： Generation of triplet excited states through radical pair intermediates has been extensively studied in molecular complexes. Similar schemes remain rare in hybrid structures of quantum dot-organic molecules, despite intense recent interest of quantum dot sensitized triplet excited state generation. Herein, we demonstrate that the efficiency of the intersystem crossing from the singlet to the triplet state in boron dipyrromethene (BODIPY) can be enhanced in CdSe quantum dot-BODIPY complexes through a radical pair intermediate state consisting of an unpaired electron in the quantum dot conduction band and that in oxidized BODIPY. By transient absorption spectroscopy, we show that the excitation of BODIPY with 650 nm light leads to the formation of a charge separated state by electron transfer from BODIPY to CdSe (with a time constant of 6.33 ± 1.13 ns), competing with internal conversion to the ground state within BODIPY, and the radical pair state decays subsequently by back charge recombination to generate a triplet excited state (with a time constant of 158 ± 28 ns) or the ground state of BODIPY. The overall quantum efficiency of BODIPY triplet excited state generation was determined to be (27.2 ± 3.0)%. The findings of efficient triplet state formation and intermediate radical pair states in this hybrid system suggest that quantum dot-molecule complexes may be a promising platform for spintronics applications.
关键词： CdSe quantum dot,radical pair intermediates,transient absorption spectroscopy,intersystem crossing,spintronics,triplet excited states,BODIPY,quantum dot-organic molecules
更新于2025-09-12 10:27:22
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Theoretical study on the low-lying electronic excited states and laser cooling feasibility of AuH molecule
摘要： To evaluate characteristics of the low-lying electronic states and the feasibility of the laser cooling of the AuH molecule, we investigate the potential energy curves (PECs), the vibrational and rotational characteristics of the ground and low-lying excited electronic states based on ab initio calculations. The PECs of the X1Σ+, A1Σ+, B1Σ+, a3Σ+, b3Σ+, e3Σ+, C1П, D1П, c3П and d3П states and the transition dipole moments among these states are calculated with the multi-reference configuration interaction method with Davidson correction and all-electron basis sets. Based on the obtained PECs, the Schr?dinger equations of nuclear movement are solved to obtain the rotational and vibrational energy levels of the electronic states. The spectroscopic parameters are obtained by fitting the obtained rotational and vibrational levels with Dunham series expansion. The matrices of the Franck-Condon factors (FCFs) dependent on the vibrational quantum numbers are obtained. The feasibility of laser cooling is explored. The FCF of the D1П (v′ = 0) ? X1Σ+ (v″ = 0) transition is 0.9862, which implies that the AuH molecule is feasible but not the much better ones for laser cooling and more pumping lasers are needed. The optical laser cooling scheme is suggested and the Einstein coefficient and the recoil temperature are calculated to evaluate the effect of the cooling scheme.
关键词： Franck-Condon factor,recoil temperature,laser cooling scheme,transition dipole moment,low-lying excited states
更新于2025-09-11 14:15:04