Photoexcited System Research Articles

Enantioselective 1,2-Carboamination of 1,3-Dienes with N-Hydroxyphthalimide (NHP) Esters Enabled by a Photoinduced Pd Catalysis.

Herein, a photoinduced, Pd-catalyzed direct 1,2-carboamination of conjugated 1,3-dienes has been successfully achieved. Sequential regioselective C-C bond and enantioselective C-N bond formation allows rapid assembly of a wide range of value-added chiral allylic amines from readily available N-hydroxyphthalimide (NHP) esters and 1,3-dienes under mild conditions. This developed protocol further demonstrates the versatility and potency of the photoexcited Pd catalytic system with a bifunctional reagent in the streamlined difunctionalization of C═C bonds.

Computation of Magnetic Exchange Couplings in Photoexcited Systems Based on KS-DFT.

Many efforts have been made in the study of optically excited spin-coupled molecules due to their appealing features for quantum information sciences. However, the characterization of the magnetic exchange couplings occurring from the photoexcitation is challenging experimentally. In this context, theoretical determinations play a critical role and must provide evaluations with rigorous and cost-effective strategies. This work presents a new approach to compute magnetic exchange couplings in photoexcited systems based on the recently generalized decomposition/recomposition method (David et al., Phys. Chem. Chem. Phys. 2024, 6, 8952-8964). This corresponds to the first application of KS-DFT in this context and offers both a completely general method and a powerful rationalization tool. This strategy is applied to mono- and biradical-based molecules recently synthesized by Kirk and co-workers.

Stochastic Schrödinger equation for hot-carrier dynamics in plasmonic systems

We present a multiscale method coupling the theory of open quantum systems with real-time ab initio treatment of electronic structure to study hot-carrier dynamics in photoexcited plasmonic systems. We combine the Markovian Stochastic Schrödinger equation with an ab initio GW coupled to the Bethe–Salpeter (BSE) equation description of the electronic degrees of freedom, interacting with a metallic nanoparticle modeled classically according to the polarizable continuum model. We apply this methodology to study the effect of relaxation (T1) and pure dephasing (T2) times on the hot-carrier dynamics in a system composed of a quantum portion described at GW/BSE level, i.e., a CHO fragment adsorbed on a vertex of a rhodium nanocube, and of the rest of the nanocube, treated classically, when irradiated with a 2.7 eV light pulse, inspired by the experimental results on plasmon-driven CO2 photoreduction. A net hole injection from rhodium to CHO is observed, with and without the classical portion of the nanocube. The nanocube effect is to enhance the generated charge population by two orders of magnitude. The nonradiative decay, via a relaxation time T1 based on the energy-gap law, produces a rapid decrease of the charge population. Results with T2 only show that a charge injection retarded with respect to the pulse, which is present in the coherent dynamics, disappears when coherence is erased.

Ultrafast terahertz Stark spectroscopy reveals the excited-state dipole moments of retinal in bacteriorhodopsin

The photoinduced all-trans to 13-cis isomerization of the retinal Schiff base represents the ultrafast first step in the reaction cycle of bacteriorhodopsin (BR). Extensive experimental and theoretical work has addressed excited-state dynamics and isomerization via a conical intersection with the ground state. In conflicting molecular pictures, the excited state potential energy surface has been modeled as a pure S[Formula: see text] state that intersects with the ground state, or in a 3-state picture involving the S[Formula: see text] and S[Formula: see text] states. Here, the photoexcited system passes two crossing regions to return to the ground state. The electric dipole moment of the Schiff base in the S[Formula: see text] and S[Formula: see text] state differs strongly and, thus, its measurement allows for assessing the character of the excited-state potential. We apply the method of ultrafast terahertz (THz) Stark spectroscopy to measure electric dipole changes of wild-type BR and a BR D85T mutant upon electronic excitation. A fully reversible transient broadening and spectral shift of electronic absorption is induced by a picosecond THz field of several megavolts/cm and mapped by a 120-fs optical probe pulse. For both BR variants, we derive a moderate electric dipole change of 5 [Formula: see text] 1 Debye, which is markedly smaller than predicted for a neat S[Formula: see text]-character of the excited state. In contrast, S[Formula: see text]-admixture and temporal averaging of excited-state dynamics over the probe pulse duration gives a dipole change in line with experiment. Our results support a picture of electronic and nuclear dynamics governed by the interaction of S[Formula: see text] and S[Formula: see text] states in a 3-state model.

Photoexcitation-induced efficient detoxification and removal of arsenite in contaminated water by a layered double hydroxide-supported polyacrylate stabilized ferrous sulfide composite

The effective detoxification and removal of arsenite (As(III)) has been widely concerned because of its strong toxicity and migration ability. In this study, we designed a layered double hydroxide-supported polyacrylate stabilized ferrous sulfide composite (PAA/FeS@LDH) and coupled it with UV excitation to purify As(III)-polluted water. The removal efficiency of As(III) under UV irradiation reached almost 100% in 120 min, and the first-order kinetic constant was 3.12 orders of magnitude higher than under dark. UV irradiation significantly accelerated the oxidation and detoxification of As(III) at the interface of PAA/FeS@LDH and treatment solution. It is attributable to the generation of reactive oxygen species (ROS) intermediates, including .O2–, .OH, and SO4.– under UV irradiation, because of the presence of the photogenerated electron-hole pairs and iron valence states cycles. Importantly, .O2– may be rapidly captured and oxidized to 1O2 on the surface of PAA/FeS@LDH that is also an important contributor to the oxidation removal of As(III). Noticeably, As(III) concentrations in the real water were rapidly reduced to below the guideline limitation of drinking water (10 μg/L) within 20 min under UV irradiation. Our outcomes provide a novel photoexcitation treatment system for the efficient detoxification and removal of As from actual wastewater.

Prediction through quantum dynamics simulations: Photo-excited cyclobutanone.

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 500fs 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.

Recent Advances in Redox-Based Z-Scheme Overall Water Splitting under Visible Light Irradiation.

Photocatalytic overall water splitting (OWS) using suspended particulate photocatalysts to produce green hydrogen has inspired continuous interest due to its low cost for easy large-scale application. The two-step photoexcitation system (Z-scheme) mimicking natural photosynthesis was proposed to efficiently use visible light for realization of efficient conversion of solar irradiation. In this Perspective, we will introduce recent advances in redox-based Z-scheme OWS systems, including iodine-based, iron-based, metal complex-based, and other special ion redox couples. The advantages and challenges of each couple and the factors affecting the Z-scheme OWS efficiency are discussed in detail. Finally, the challenges and feasible solutions for the achievement of highly efficient Z-scheme OWS are then outlined. This Perspective provides guidance on how to construct a Z-scheme OWS system and enhance photocatalytic performance.

TRAVOLTA: GPU acceleration and algorithmic improvements for constructing quantum optimal control fields in photo-excited systems

We present an open-source software package, TRAVOLTA (Terrific Refinements to Accelerate, Validate, and Optimize Large Time-dependent Algorithms), for carrying out massively parallelized quantum optimal control calculations on GPUs. The TRAVOLTA software package is a significant overhaul of our previous NIC-CAGE algorithm and also includes algorithmic improvements to the gradient ascent procedure to enable faster convergence. We examine three different variants of GPU parallelization to assess their performance in constructing optimal control fields in a variety of quantum systems. In addition, we provide several examples with extensive benchmarks of our GPU-enhanced TRAVOLTA code to show that it generates the same results as previous CPU-based algorithms but with a speedup that is more than ten times faster. Our GPU enhancements and algorithmic improvements enable large quantum optimal control calculations that can be efficiently and routinely executed on modern multi-core computational hardware. Program summaryProgram Title: TRAVOLTACPC Library link to program files:https://doi.org/10.17632/grwppm37rn.1Licensing provisions: GNU General Public License 3Programming language: C++, openBLAS, and CUDASupplementary material: Brief review of LU decomposition, raw numerical values used to generate Fig. 6 in the main text, and input examples for the TRAVOLTA software package.Nature of problem: The TRAVOLTA software package utilizes GPU accelerated routines and new algorithmic improvements to compute optimized electric fields that can drive a system from a known initial vibrational eigenstate to a specified final quantum state with a large (≈1) transition probability.Solution method: Quantum control, GPU acceleration, analytic gradients, Crank-Nicolson propagation, and gradient ascent optimization.

Chiral-induced spin selectivity in photo-induced electron transfer: Investigating charge and spin dynamics in a master equation framework.

Investigating the role of chiral-induced spin selectivity in the generation of spin correlated radical pairs in a photoexcited donor-chiral bridge-acceptor system is fundamental to exploit it in quantum technologies. This requires a minimal master equation description of both charge separation and recombination through a chiral bridge. To achieve this without adding complexity and entering in the microscopic origin of the phenomenon, we investigate the implications of spin-polarizing reaction operators to the master equation. The explicit inclusion of coherent evolution yields non-trivial behaviors in the charge and spin dynamics of the system. Finally, we apply this master equation to a setup comprising a molecular qubit attached to the donor-bridge-acceptor molecule, enabling qubit initialization, control, and read-out. Promising results are found by simulating this sequence of operations assuming realistic parameters and achievable experimental conditions.

Real-Time GW-Ehrenfest-Fan-Migdal Method for Nonequilibrium 2D Materials.

Quantum simulations of photoexcited low-dimensional systems are pivotal for understanding how to functionalize and integrate novel two-dimensional (2D) materials in next-generation optoelectronic devices. First-principles predictions are extremely challenging due to the simultaneous interplay of light-matter, electron-electron, and electron-nuclear interactions. We here present an advanced ab initio many-body method that accounts for quantum coherence and non-Markovian effects while treating electrons and nuclei on equal footing, thereby preserving fundamental conservation laws like the total energy. The impact of this advancement is demonstrated through real-time simulations of the complex multivalley dynamics in a molybdenum disulfide (MoS2) monolayer pumped above gap. Within a single framework, we provide a parameter-free description of the coherent-to-incoherent crossover, elucidating the role of microscopic and collective excitations in the dephasing and thermalization processes.

Room Temperature Electron Spin Coherence in Photogenerated Molecular Spin Qubit Candidates.

One of the main challenges in the emerging field of molecular spintronics is the identification of new spin qubit materials for quantum information applications. In this regard, recent work has shown that photoexcited chromophore-radical systems are promising candidates to expand our repertoire of suitable candidate molecules. Here, we investigate a series of three chromophore-radical compounds composed of a perylene diimide (PDI) chromophore and a stable 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radical by transient electron paramagnetic resonance (EPR) techniques. We explore the influence of isotope labeling of the TEMPO moiety on the EPR spectra and electron spin coherence times of the molecular quartet states generated upon photoexcitation and illustrate that (i) a coherent manipulation of the spin state is possible in these systems even at room temperature and that (ii) a spin coherence time of 0.7 μs can be achieved under these conditions. This demonstration of electron spin coherence at ambient temperatures paves the way for practical applications of such systems in functional molecular devices.

Semiconductors-based Z-scheme materials for photoelectrochemical water splitting: A review

Photoelectrochemical (PEC) water splitting is among the most promising approaches for a potentially clean and renewable source for hydrogen fuel from the splitting of water into hydrogen and oxygen using light source and energy conversion due to its practical efficiency. The innovative approach is the construction of a two-step photoexcitation system, often called a Z-scheme photocatalysis system, which mimics natural photosynthesis. The PEC splitting of water using various Z-scheme materials is initiated by the direct absorption of a photon, which creates separated electrons and holes in the energy band gap of the material. A Z-scheme system employs two photocatalysts, one producing H2 and the other O2, usually with the aid of an electron shuttle. This review focuses on the current state of research on nanoscale-enhanced Z-scheme photocatalyst materials for the water splitting reaction. Additionally, the recent advances achieved in especially metal oxides, metal sulfides, g-C3N4, and semiconductors-based Z-scheme materials as photocatalyst systems for water-splitting, are also covered.

Properties and applications of photoexcited chromophore-radical systems.

Photoexcited organic chromophore-radical systems hold great promise for a range of technological applications in molecular spintronics, including quantum information technology and artificial photosynthesis. However, further development of such systems will depend on the ability to control the magnetic properties of these materials, which requires a profound understanding of the underlying excited-state dynamics. In this Review, we discuss photogenerated triplet-doublet systems and their potential to be used for applications in molecular spintronics. We outline the theoretical description of the spin system in the different coupling regimes and the invoked excited-state mechanisms governing the generation and transfer of spin polarization. The main characterization techniques used to evaluate the optical and magnetic properties of chromophore-radical systems are discussed. We conclude by giving an overview of previously investigated covalently linked triplet-radical systems, and highlight the need for further systematic investigations to improve our understanding of the magnetic interactions in such systems.

Antiparallel alignment of the two angular momenta in a photoexcited dysprosium–phthalocyanine complex

The intramolecular interaction between a localized 4f-electronic system and a photo-excited macrocyclic π-conjugated system was investigated in a mono-phthalocyaninato dysprosium(iii) complex.

Tailoring the superposition of finite-momentum valley exciton states in transition-metal dichalcogenide monolayers by using polarized twisted light

A twisted light is a spatially structured light that carries quantized orbital angular momenta (OAM), being a new degree of freedom useful in quantum information technology in addition to that of intrinsic spin angular momentum (SAM), i.e., polarization. Using polarized twisted light to excite valley excitons in transition-metal dichalcogenide monolayers (TMD-ML's) sets up an intriguing photoexcited system which couples comprehensively the excitonic and photonic multi-degrees of freedom, including the center-of-mass motion and valley polarization of exciton and the both optical OAM and SAM. In this work, we present a systematic theoretical investigation of the photoexcited valley excitons in TMD-ML's by polarized Laguerre-Gaussian beams, one of the best known twisted light (TL). We show that the photoexcitation of polarized TL incident to a TMD-ML leads to the formation of the superposition of finite-momentum exciton (SFME) states, spatially localized with the OAM- and SAM-encoded geometrical patterns.

Ultrafast X-ray Spectroscopy of Haem Proteins

In this article we revisit our recent picosecond and femtosecond X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) experiments, probing the ultrafast electronic and geometric evolution of photoexcited haem proteins, namely ferrous Nitrosyl Myoglobin (MbNO) and ferric Cytochrome c (Cyt c). We show through these two examples, combined with results from ultrafast optical spectroscopy, the universal behavior of the excited state dynamics of ferric and ferrous complexes. Regardless of the type of ligand, its dissociation or lack thereof, or the metal oxidation state, the photoexcited system relaxes through a cascade of excited spin states leading to formation of a high spin state, which in the case of the haem is a domed porphyrin.

Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: An ab-initio perspective

Coherence and de-coherence are the most fundamental steps that follow the initial photo-excitation occurring in typical pump-and-probe experiments. Indeed, the initial external laser pulse transfers coherence to the system in terms of creation of multiple electron–hole pairs excitation. The excitation concurs both to the creation of a finite carriers density and to the appearance of induced electromagnetic fields. The two effects, to a very first approximation, can be connected to the simple concepts of populations and oscillations. The dynamics of the system following the initial photo-excitation is, thus, entirely dictated by the interplay between coherence and de-coherence. This interplay and the de-coherence process itself, is due to the correlation effects stimulated by the photo-excitation. Single-particle, like the electron–phonon, and two-particles, like the electron–electron, scattering processes induce a complex dynamics of the electrons that, in turn, makes the description of the correlated and photo-excited system in terms of pure excitonic and/or carriers populations challenging.

Electronic relaxation of photoexcited open and closed shell adsorbates on semiconductors: Ag and Ag2 on TiO2.

A theoretical treatment based on the equations of motion of an electronic reduced density matrix, and related computational modeling, is used to describe and calculate relaxation times for nanostructured TiO2(110) surfaces, here for Ag and Ag2 adsorbates. The theoretical treatment deals with the preparation of a photoexcited system under two different conditions, by steady light absorption with a cutoff and by a light pulse, and describes the following relaxation of electronic densities. On the computational modeling, results are presented for electronic density of states, light absorbance, and relaxation dynamics, comparing results for Ag and Ag2 adsorbates. The aim of this work is to provide insight on the dynamics and magnitude of relaxation rates for a surface with adsorbed open- and closed-shell Ag species to determine whether the advantages in using them to enhance light absorbance remain valid in the presence of charge density relaxation. Different behaviors can be expected depending on whether the adsorbate particles (Ag metal clusters in our present choice) have electronic open-shell or closed-shell structures. Calculated electron and hole lifetimes are given for pure TiO2(110), Ag/TiO2(110), and Ag2/TiO2(110). The present results, while limited to chosen structures and photon wavelengths, show that relaxation rates are noticeably different for electrons and holes, but comparable in magnitude for pure and adsorbate surfaces. Overall, the introduction of the adsorbates does not lead to rapid loss of charge carriers, while they give large increases in light absorption. This appears to be advantageous for applications to photocatalysis.

Antiparallel Coupling between a 4f System and a Photoexcited Cyclic π System in a Dysprosium(III) Monoporphyrinato Complex

Magnetic coupling resulted by an orbital angular momentum L of a photoexcited cyclic π-conjugated system and total angular momentum J of a localized 4f electronic system in [Dy(TPP)(cyclen)]Cl (TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) has been identified using magnetic circular dichroism (MCD). The MCD A-term patterns of the compound show a negative increment in the intensity by decreasing temperature and nonproportionality to the magnetic field. This phenomenon is experimentally observed for the first time in porphyrin-based lanthanide complexes and indicates the presence of the J-L interaction, with the preferred orientation being antiparallel. A theoretical model in which J and L are assumed to couple antiferromagnetically yielded a quantitative agreement to the experimental data of varied-temperature and varied-magnetic-field MCD spectral measurements. The ab initio calculations were performed, revealing the relationship between two orbital angular momenta, i.e., L(π) and L(f), which result from the delocalized π system and the localized 4f system, respectively.

Complementary Photo-Synapses Based on Light-Stimulated Porphyrin-Coated Silicon Nanowires Field-Effect Transistors (LPSNFET).

Neuromorphic computing has emerged as the high-energy-efficiency and intelligent solution for processing sensory data. As a potential alternative to neuromorphic computing, photo-excited synaptic systems can integrate the functions of optoelectronic sensing and synaptic computing to realize the low-power and high-performance visual perception. However, one major challenge in high-efficient photo-excited synaptic system is to realize the complementarily enhanced and inhibited synaptic behaviors with small hardware cost as possible. Another challenge is to fabricate the photo-synapse devices with complementary metal oxide semiconductor (CMOS)-compatible process to achieve high enough integration density for practical application. Here, a CMOS-compatible Light-stimulated Porphyrin-coated Silicon Nanowire Field Effect Transistor (LPSNFET) technology is proposed and developed to form the complementary photo-synapses with only two CMOS-like transistors. LPSNFET exhibits fivefold improvement in photo-sensitivity compared to the bare silicon nanowire (SiNW) devices, and can still show obvious responses when incident illumination power is as low as 0.1 mW cm-2 . Moreover,itenables tunable dynamic synaptic plasticity and versatile synaptic functions. Especially, the complementarily enhanced and inhibited behaviors can be realized by modulating SiNW/porphyrin interface via simply changing the MOS type of LPSNFET, which acts like the photonic counterpart of CMOS technology to provide the basic brick for building complex neuromorphic circuits efficiently and economically. Finally, the CMOS process compatibility of LPSNFET provides potential application in future large scale in-sensor computing.