Excited Research Articles

Solvent Effects on Spin-Orbit Charge-Transfer Intersystem Crossing in Aryl-Substituted Boron-dipyrromethene Donor-Acceptor Dyads.

In heavy-atom-free organic molecules, the rate of triplet generation through charge recombination, as dictated by the El-Sayed rule, can be enhanced by 101-102 times compared with the rate of spontaneous spin flipping between π-π* orbitals. This mechanism is known as the spin-orbit charge-transfer intersystem crossing (SOCT-ISC). Within the framework of the SOCT-ISC mechanism, facilitating the generation of charge-separated (CS) states and suppressing the spin-allowed direct charge recombination to the ground state are pivotal for maximizing the efficiency of generating localized triplet states. Herein, a series of orthogonal aryl-substituted boron-dipyrromethene dyads were studied by time-resolved spectroscopy to unravel the multichannel competitive relationships in the SOCT-ISC mechanism. The energy level of the electron donor and the stabilization of the solvent effect to the charge-transfer state are reflected in the Gibbs free energy changes of the electron transfer and recombination reactions, leading to significantly different triplet quantum yields. Additionally, solvation-induced electronic coupling changes in excited states lead to the fact that the spin-allowed charge recombination rate cannot be well simply predicted by the Marcus inverted region but has to consider the specific excited-state dynamics in optimizing the proportion of triplet generation channels based on charge recombination.

Hybrid Local and Charge Transfer Emitters Utilizing Hyperconjugation Effect Towards Solution-Processed Ultra-Deep-Blue OLEDs with External Quantum Efficiency Approaching 12.

Hybrid local and charge transfer (HLCT) excited state materials, which possess weak donor-acceptor (D-A) pure organic structures, deserve one of the most promising efficient and stable blue emitters. Through high-lying reverse intersystem crossing (hRISC) process, 75% triplet excitons generated by electrical excitation could be harvested and utilized in organic light-emitting diodes (OLEDs). However, there are still significant challenges to achieve high-efficiency ultra-deep-blue HLCT emitters with low Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate y values. Here, a series of novel blue HLCT emitters based on spiro[1,8-diazafluorene-9,2'-imidazole] structure were designed and synthesized by fine-tuning the spiro[fluorene-9,2'-imidazole] core structure in our previous work through heteroatom substitution and hyperconjugation effect. The target emitters were endowed with excellent photophysical and electrochemical merits, thermal stability and solution processibility. The solution-processed OLED device based on 4',5'-bis(4-(9H-carbazol-9-yl)phenyl)spiro[1,8-diazafluorene-9,2'-imidazole] (NFIP-CZ) achieved efficient ultra-deep-blue emission (CIEx,y = 0.1581, 0.0422) with the maximum external quantum efficiency (EQEmax), maximum current efficiency (CEmax) and maximum power efficiency (PEmax) of 11.94%, 4.07 cd·A-1 and 2.56 lm·W-1. The record EQE is a breakthrough in both solution-processed and vacuum vapor deposition ultra-deep-blue HLCT-OLEDs currently.

Guest-Mediated Modulation of Photophysical Pathways in a Coronene Bisimide Cyclophane.

The properties and functions of chromophores utilized by nature are strongly affected by the environment formed by the protein structure in the cells surrounding them. This concept is transferred here to host-guest complexes with the encapsulated guests acting as an environmental stimulus. A new cyclophane host based on coronene bisimide is presented that can encapsulate a wide variety of planar guest molecules with binding constants up to (4.29 ± 0.32) × 1010 M-1 in chloroform. Depending on the properties of the chosen guest, the excited state deactivation of the coronene bisimide chromophore can be tuned by the formation of host-guest complexes toward fluorescence, exciplex formation, charge separation, room-temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). The photophysical processes were investigated by UV/vis absorption, emission, and femto- and nanosecond transient absorption spectroscopy. To enhance the TADF, two different strategies were used by employing suitable guests: the reduction of the singlet-triplet gap by exciplex formation and the external heavy atom effect. Altogether, by using supramolecular host-guest complexation, a versatile multimodal chromophore system is achieved with the coronene bisimide cyclophane.

Sensitivity Analysis of Excited-State Population in Plasma Based on Relative Entropy.

A highly versatile evaluation method is proposed for transient plasmas based on statistical physics. It would be beneficial in various industrial sectors, including semiconductors and automobiles. Our research focused on low-energy plasmas in laboratory settings, and they were assessed via our proposed method, which incorporates relative entropy and fractional Brownian motion, based on a revised collisional-radiative model. By introducing an indicator to evaluate how far a system is from its steady state, both the trend of entropy and the radiative process' contribution to the lifetime of excited states were considered. The high statistical weight of some excited states may act as a bottleneck in the plasma's energy relaxation throughout the system to a steady state. By deepening our understanding of how energy flows through plasmas, we anticipate potential contributions to resolving global environmental issues and fostering technological innovation in plasma-related industrial fields.

Porphyrin photosensitizer molecules as effective medicine candidates for photodynamic therapy: electronic structure information aided design.

Traditional photosensitizers (PS) in photodynamic therapy (PDT) have restricted tissue penetrability of light and a lack of selectivity for tumor cells, which diminishes the efficiency of PDT. Our aim is to effectively screen porphyrin-based PS medication through computational simulations of large-scale design and screening of PDT candidates via a precise description of the state of the light-stimulated PS molecule. Perylene-diimide (PDI) shows an absorption band in the near-infrared region (NIR) and a great photostability. Meanwhile, the insertion of metal can enhance tumor targeting. Therefore, on the basis of the original porphyrin PS segments, a series of metalloporphyrin combined with PDI and additional allosteric Zn-porphyrin-PDI systems were designed and investigated. Geometrical structures, frontier molecular orbitals, ultraviolet-visible (UV-vis) absorption spectra, adiabatic electron affinities (AEA), especially the triplet excited states and spin-orbit coupling matrix elements (SOCME) of these expanded D-A porphyrin were studied in detail using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. PS candidates, conforming type I or II mechanism for PDT, have been researched carefully by molecular docking which targeted Factor-related apoptosis (Fas)/Fas ligand (Fasl) mediated signaling pathway. It was found that porphyrin-PDI, Fe2-porphyrin-PDI, Zn-porphyrin-PDI, Mg-porphyrin-PDI, Zn-porphyrin combined with PDI through single bond (compound 1), and two acetylenic bonds (compound 2) in this work would be proposed as potential PS candidates for PDT process. This study was expected to provide PS candidates for the development of novel medicines in PDT.

Lifetimes of excited states in 16\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{16}$$\\end{document}C as a benchmark for ab initio developments

Lifetimes of higher-lying states (22+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2_2^+$$\\end{document} and 41+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$4_1^+$$\\end{document}) in 16\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{16}$$\\end{document}C have been measured, employing the Gammasphere and Microball detector arrays, as key observables to test and refine ab initio calculations based on interactions developed within chiral Effective Field Theory. The presented experimental constraints to these lifetimes of τ(22+)=[244,446]fs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au ({2_2^+}) = [\\,244, 446]\\,~\ extrm{fs}$$\\end{document} and τ(41+)=[1.8,4]ps\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au ({4_1^+}) = [\\,1.8, 4]\\,~\ extrm{ps}$$\\end{document}, combined with previous results on the lifetime of the 21+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2_1^+$$\\end{document} state of 16\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{16}$$\\end{document}C, provide a rather complete set of key observables to benchmark the theoretical developments. We present No-Core Shell-Model calculations using state-of-the-art chiral 2- (NN) and 3-nucleon (3N) interactions at next-to-next-to-next-to-leading order for both the NN and the 3N contributions and a generalized natural-orbital basis (instead of the conventional harmonic-oscillator single-particle basis) which reproduce, for the first time, the experimental findings remarkably well. The level of agreement of the new calculations as compared to the CD-Bonn meson-exchange NN interaction is notable and presents a critical benchmark for theory.

Steric and Electronic Influence of Excited-State Decay in Cu(I) MLCT Chromophores.

ConspectusFor the past 11 years, a dedicated effort in our research group focused on fundamentally advancing the photophysical properties of cuprous bis-phenanthroline-based metal-to-ligand charge transfer (MLCT) excited states. We rationalized that, by gaining control over the numerous factors limiting the more widespread use of CuI MLCT photosensitizers, they would be readily adopted in numerous light-activated applications given the earth-abundance of copper and the extensive library of 1,10-phenanthrolines developed over the last century. Significant progress has been achieved by recognizing valuable structure-property concepts developed by other researchers in tandem with detailed ultrafast and conventional time-scale investigations, in-silico-inspired molecular designs to predict spectroscopic properties, and applying novel synthetic methodologies. Ultimately, we achieved a plateau in exerting cooperative steric influence to control CuI MLCT excited state decay. This led to combining sterics with π-conjugation and/or inductive electronic effects to further exert control over molecular photophysical properties. The lessons gleaned from our studies of homoleptic complexes were recently extended to heteroleptic bis(phenanthrolines) featuring enhanced visible light absorption properties and long-lived room-temperature photoluminescence. This Account navigates the reader through our intellectual journey of decision-making, molecular and experimental design, and data interpretation in parallel with appropriate background information related to the quantitative characterization of molecular photophysics using CuI MLCT chromophores as prototypical examples.Initially, CuI MLCT excited states, their energetics, and relevant structural conformation changes implicated in their photophysical decay processes are described. This is followed by a discussion of the literature that motivated our research in this area. This led to our first molecular design in 2013, achieving a 7-fold increase in excited state lifetime relative to the current state-of-the-art. The lifetime and photophysical property enhancement resulted from using 2,9-branched alkyl groups in conjunction with flanking 3,8-methyl substituents, a strategy we adapted from the McMillin group, which was initially described in the late 1990s. Applications of this newly conceived chromophore are presented in solar hydrogen-producing photocatalysis, photochemical upconversion, and photosensitization of [4 + 4] anthracene dimerization of potential interest in thermal storage of solar energy in metastable intermediates. Ultrafast transient absorption and fluorescence upconversion spectroscopic characterization of this and related CuI molecules inform the resultant photophysical properties and vice versa, so the most comprehensive structure-property understanding becomes realized when these experimental tools are collectively utilized to investigate the same series of molecules. Computationally guided structural designs generated newly conceived molecules featuring visible light-harvesting and 2,9-cycloalkane substituted complexes. The latter eventually produced record-setting excited state lifetimes in molecules leveraging both cooperative steric influence and electronic inductive effects. Using photoluminescence data from structurally homologous CuI MLCT excited states collected over 44 years, an energy gap correlation successfully modeled the data spanning a 0.3 eV emission energy range. Finally, a new research direction is revealed detailing structure-photophysical property relationships in heteroleptic CuI phenanthroline chromophores that are photoluminescent at room temperature.

Monosilicon Derivatives of Phenanthrene and Pyrene as Potential Singlet Fission Materials for High-Performance Solar Cells.

Singlet fission (SF) is a process in which the energy of a singlet-excited molecule is divided into two triplet excitations. This is a special case of an internal conversion that is spin-allowed and extremely fast. Ideally, this process utilizes one photon to produce two electron-hole pairs. In tandem with a layer of singlet fission material, conventional solar cells can achieve improved efficiency by utilizing higher-energy photons. This density functional theory study provides information about additional efficient SF chromophores that were theoretically modeled by functionalizing phenanthrene and pyrene via site-specific monosilicon substitutions. The SF capabilities of the derivatives were evaluated by calculating the SF thermodynamic driving force (ΔESF) and the excited state's molecular planarity. The most promising monosilicon derivatives with SF capabilities are 3-silaphenanthrene and 1-silapyrene for each family, respectively. All phenanthrene and pyrene monosilicon derivatives are strong closed-shell species, because their multiple diradical characteristics are close to zero. Based on these results, 3-silaphenanthrene and 1-silapyrene were selected for electron excitation analysis, which further demonstrated that the monosilicon functionalization of phenanthrene and pyrene led to a transfer from local excitation characters to hybridized local and charge-transfer characters of the excited states, resulting in a significant change from endoergic to exoergic in the SF chromophores.

Ab initio the thermodynamic properties and UV spectrum of AlCl+

AlCl+ as a potential interstellar molecule has attracted significant attention, but gaps remain in our understanding of its thermodynamic properties and spectral line intensities. This study employed the icMRCI+Q method to compute potential energy curves for the 13 Λ-S states of AlCl+. Based on these curves, spectroscopic parameters and vibrational–rotational energy levels were determined. Subsequently, partition functions were calculated over a temperature range from 50 K to 10000 K, and the thermodynamic properties were derived. Using transition dipole moments, the UV spectra for transitions from the ground state (X2Σ+) to the third excited state (22Π) were computed at 298.15 K.

Bonding and Interactions in UO22+ for Ground and Core Excited States: Extracting Chemistry from Molecular Orbital Calculations.

Theoretical analyses of actinyls are necessary in order to understand and correctly interpret the chemical and physical properties of these molecules. Here, wave functions of Uranyl, UO22+, are considered for the ground state and for the core excited states where an electron is promoted from the U 3d5/2 shell into a low-lying unoccupied orbital that is U 5f antibonding with the ligand, O, orbitals. A focus is on the application of novel theoretical methods to the analysis of these wave functions so that measurements, especially with X-ray absorption, can be related to the UO22+ chemical bonding. The bond covalency is examined with these theoretical methods. The study includes how the covalent character is different for the ground and excited configurations and how this character changes as the U-O distance is changed. Furthermore, analyses are mode of how many-body effects may modify excitation energies and X-ray adsorption intensities. This includes determining the extent to which a single configuration provides a satisfactory model for the UO22+ wave functions. Two distinct types of many-body effects are considered. One involves the angular momentum coupling of the open shell electrons in the excited states to yield correct multiplets. The second adds excitations from shells that are bonding into the antibonding open shell space. These excitations are essential to properly describe the X-ray adsorption. While these many-body effects must be taken into account, their importance and their role can be explained and understood using orbitals and orbital occupations.

1,4-Benzodioxane substituted aza-BODIPY: towards photostable yet efficient triplet photosensitizer.

We report herein the synthesis of aza-BODIPY substituted with 1,4-benzodioxane-6-yl substituents at 3,5 positions of the chromophore system. Both pyrrole rings of the aza-BODIPY in question were substituted with bromine atoms in order to induce highly desirable photophysical properties, such as highly populated excited triplet state (T1) and long excited triplet-state lifetime (τT) of 21 µs. The photosensitized oxygenation of a model compounds, viz. DPBF, points to a high singlet oxygen and/or other ROS formation quantum yield of 0.42. The photosensitizer studied exhibited an absorption band within the so-called "therapeutic window", with λabs 678 nm. As estimated by CV/DPV measurements the 1,4-benzodioxane-6-yl substituted aza-BODIPYs studied exhibited a multi-electron oxidations at a relatively low potentials (Eox), pointing to the very good electron-donating properties of these molecules. High photostability and thermal stability was observed for all compounds studied. The good singlet oxygen quantum yield measured combined with an exceptional photostability makes this aza-BODIPY a promising candidate for applications such as photocatalysis and photodynamic therapy (PDT).

Quantitative Structure Photovoltaic Properties Relationship of Coumarin Dyes Derived

The performance of an organic solar cell is strongly influenced by the structure of the photosensitizer. In this work, the open-circuit voltage (<I>V<SUB>OC</SUB></I>) and conversion efficiency (<i>η</i>) of a series of coumarin dyes are quantitatively related to the structure of nine coumarin derivatives. The Quantitative Structure Property Relationship (QSPR) is performed using the statistical method of multiple linear regression. In addition, descriptors determined from the ground state at the Cam_B3lyp/6-31G(d, p) level of theory and from the 2D structure of the molecules are mathematically related to the photovoltaic properties. These VOC and <i>η </i>models are accredited with very good statistical indicators (<I>R<sup>2</sup></I> = 0.906 and 0.918; Q<sub>cv</sub><sup>2</sup>= 0.845 and 0.849; S= 0.045 and 0.112; F = 14.524 and 16.846). These statistical indicators confirm the robustness and performance of the models developed. The results show that Voc improves with decreasing surface tension (<i>ts</i>) and increasing number of cycles (<i>cycle</i>). As for the conversion efficiency of light radiation into electrical energy, it is optimal when the light harvesting efficiency (<i>LHE<sub>th</sub></i>) and the excited state lifetime (<i>τ<sub>th</sub></i>) are high. In conclusion, these models have good predictive capabilities and can be used to predict and explain the open-circuit voltage and efficiency of coumarin derivatives that belong to the same field of application.

Internal Conversion Cascade in a Carbon Nanobelt: A Multiconfigurational Quantum Dynamical Study.

Carbon nanobelts feature intriguing photophysical properties, due to their high symmetry and structural rigidity. Here, we consider a (6,6) armchair carbon nanobelt, i.e., the very first carbon nanobelt to be synthesized [Povie et al., Science 2017, 356, 172] and characterize the internal conversion dynamics using multiconfigurational quantum dynamics via the multi-layer multiconfiguration time-dependent Hartree (ML-MCTDH) method. A symmetry-adapted linear vibronic coupling Hamiltonian for 26 electronic states and 210 vibrational modes is employed. Electronic excitations are found to decay through a dense manifold of excited states, which interact via multiple conical intersections, while inducing minimal geometry change. It is shown that a rapid coherent decay, exhibiting a nonvanishing quantum flux on a time scale of less than 50 fs, transitions toward a slower, decoherent decay at longer times. As previously suggested in the literature, electronic relaxation is hindered by phonon bottlenecks such that a stepwise internal conversion cascade is observed. The computed vibronic absorption spectrum is shown to be in good agreement with the experimental spectrum.

Unidirectional photoisomerisation in a dual channel proton transfer molecule rhodamine B based Schiff Base: A ratiometric pH sensor

In this article we have presented the synthesis, characterisation and spectral study of a newly designed fluorophore, (E)-2-((3-(benzo[d]oxazol-2-yl)-5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro [isoindoline-1,9′-xanthen]-3-one (RHHBO) which has two possible six member intramolecular hydrogen bonded networks capable for dual channels proton transfer reaction − one towards the N atom of oxazole moiety and the other towards the N atom of rhodamine moity. Details steady state and time resolved spectral analysis of RHHBO and a comparison of spectral features of control compounds 2-(2-hydroxyphenyl)benzoxazole (HBO), (E)-4-bromo-2-(hydrazonomethyl)phenol (HBN) and (E)-2-((5-bromo-2-hydroxybenzylidene)amino)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (RH) having only single proton transfer site reveal that excited state intramolecular proton transfer (ESIPT) in RHHBO occurs towards the rhodamine side but not towards the oxazole side. Interestingly, RHHBO shows different fluorescence colour in acidic and basic medium and hence can be used ratiometric emission based pH sensor.

Divalent tin activator for Nd3+/Yb3+ emission in lanthanum borate glass and its impact on inter-ionic phenomena and thermometry

The co-existence of divalent tin activator and Nd3+/Yb3+ rare earths in the borate glasses were utilized and examined to achieve the effective enhancement of the useful near-infrared emission in the wide spectral region. The UV Sn2+ excitation is extremely relevant for the effectiveness of both (Nd,Yb) near-infrared emission, however, Sn-Nd energy transfer efficiency is particularly prominent. The different advantageous inter-ionic phenomena made it possible to explore the diverse energy transfer routes leading to the population of the relevant ytterbium and neodymium excited states. Consequently, adequate multi-model temperature sensing can be proposed and verified considering single-doped and co-doped borate glass systems. The dissimilar effect of temperature on the complementary Sn2+, Nd3+ and Yb3+ optical transitions was investigated in detail. Employing the temperature-dependent spectra of optically active ions, high values of temperature relative sensitivity (1.3 % K−1) were estimated especially in the physiological range (30 – 75 ⁰C).

Computational Exploration of the Mechanism of Action of a Sorafenib-Containing Ruthenium Complex as an Anticancer Agent for Photoactivated Chemotherapy.

Ruthenium(II) polypyridyl complexes are being tested as potential anticancer agents in different therapies, which include conventional chemotherapy and light-activated approaches. A mechanistic study on a recently synthesized dual-action Ru(II) complex [Ru(bpy)2(sora)Cl]+ is described here. It is characterized by two mono-dentate leaving ligands, namely, chloride and sorafenib ligands, which make it possible to form a di-aquo complex able to bind DNA. At the same time, while the released sorafenib can induce ferroptosis, the complex is also able to act as a photosensitizer according to type II photodynamic therapy processes, thus generating one of the most harmful cytotoxic species, 1O2. In order to clarify the mechanism of action of the drug, computational strategies based on density functional theory are exploited. The photophysical properties of the complex, which include the absorption spectrum, the kinetics of ISC, and the character of all the excited states potentially involved in 1O2 generation, as well as the pathway providing the di-aquo complex, are fully explored. Interestingly, the outcomes show that light is needed to form the mono-aquo complex, after releasing both chloride and sorafenib ligands, while the second solvent molecule enters the coordination sphere of the metal once the system has come back to the ground-state potential energy surface. In order to simulate the interaction with canonical DNA, the di-aquo complex interaction with a guanine nucleobase as a model has also been studied. The whole study aims to elucidate the intricate details of the photodissociation process, which could help with designing tailored metal complexes as potential anticancer agents.

A second-order kinetic model for global analysis of vibrational polariton dynamics.

The interaction between cavity photons and molecular vibrations leads to the formation of vibrational polaritons, which have demonstrated the ability to influence chemical reactivity and change material characteristics. Although ultrafast spectroscopy has been extensively applied to study vibrational polaritons, the nonlinear relationship between signal and quantum state population complicates the analysis of their kinetics. Here, we employ a second-order kinetic model and transform matrix method (TMM) to develop an effective model to capture the nonlinear relationship between the two-dimensional IR (or pump-probe) signal and excited state populations. We test this method on two types of kinetics: a sequential relaxation from the second to the first excited states of dark modes, and a Raman state relaxing into the first excited state. By globally fitting the simulated data, we demonstrate accurate extraction of relaxation rates and the ability to identify intermediate species by comparing the species spectra with theoretical ground truth, validating our method. This study demonstrates the efficacy of a second-order TMM approximation in capturing essential spectral features with up to 10% excited state population, simplifying global analysis and enabling straightforward extraction of kinetic parameters, thus empowering our methodology in understanding excited-state dynamics in polariton systems.

Impact of Classical and Quantum Light on Donor-Acceptor-Donor Molecules.

Investigations of entangled and classical two-photon absorption have been carried out for six donor (D)-acceptor (A)-donor (D) compounds containing the dithieno pyrrole (DTP) unit as donor and acceptors with systematically varied electronic properties. Comparing ETPA (quantum) and TPA (classical) results reveals that the ETPA cross section decreases with increasing TPA cross section for molecules with highly off-resonant excited states for single-photon excitation. Theory (TDDFT) results are in semiquantitative agreement with this anticorrelated behavior due to the dependence of the ETPA cross section but not TPA on the two-photon excited state lifetime. The largest cross section is found for a DTP derivative that has a single photon excitation energy closest to resonance with half the two-photon excitation energy. These results are important for the possible use of quantum light for low-intensity energy-conversion applications.

Prerelaxation in quantum, classical, and quantum-classical two-impurity models

We numerically study the relaxation dynamics of impurity-host systems, focusing on the presence of long-lived metastable states in the nonequilibrium dynamics after an initial excitation of the impurities. In generic systems, an excited impurity coupled to a large bath at zero temperature is expected to relax and approach its ground state over time. However, certain exceptional cases exhibit metastability, where the system remains in an excited state on timescales largely exceeding the typical relaxation time. We study this phenomenon for three prototypical impurity models: a tight-binding quantum model of independent spinless fermions on a lattice with two stub impurities, a classical-spin Heisenberg model with two weakly coupled classical impurity spins, and a tight-binding quantum model of independent electrons with two classical impurity spins. Through numerical integration of the fundamental equations of motion, we find that all three models exhibit similar qualitative behavior: complete relaxation for nearest-neighbor impurities and incomplete or strongly delayed relaxation for next-nearest-neighbor impurities. The underlying mechanisms leading to this behavior differ between models and include impurity-induced bound states, emergent approximately conserved local observables, and exact cancellation of local and nonlocal dissipation effects. Published by the American Physical Society 2024

Investigation of the temperature-dependent photoluminescence characteristics in Mn2+-doped (PEA)2PbBr4 perovskite

The two-dimensional organic-inorganic hybrid perovskites demonstrate significant potential for use in photodetectors and white light-emitting diodes. In this study, we successfully synthesized pure and Mn2+-doped (PEA)2PbBr4 perovskite via rapid crystallization. The morphology, structure, magnetic properties, and optical characteristics of them were comprehensively characterized. The unusual behavior of free exciton emission is mainly attributed to electron-phonon coupling and negative thermal quenching effects. The self-trapped exciton emission results from self-trapped excited states and electron-phonon coupling. Moreover, energy transfer phenomena are observed between free exciton emission, self-trapped exciton emission, and Mn2+ emission. These findings offer valuable insights into the luminescence mechanism of two-dimensional layered perovskites.