Excited Energy Levels Research Articles

Intracage vibrations and Zeeman effect in Y3N@C80 single-molecule transistors

Clusterfullerenes, which contain a cluster rather than single-atom inclusions, exhibit more complex internal structures and greater degrees of freedom for motion. Trimetallic nitride clusterfullerenes have attracted significant attention due to their diversity and potential applications, among which Y3N@C80 stands out for its charge-transfer characteristics in electronic excitations, owing to the unique distribution of molecular orbitals near the Fermi level. Here, we have fabricated single-molecule transistor devices using Y3N@C80. Transport measurements at liquid helium temperature revealed a series of excited state energy levels, which were matched to corresponding vibrational modes through comparison with Raman spectra and density functional theory calculations. Additionally, we measured charge-state-dependent magnetic responses, revealing the electron and spin-filling patterns of the molecular orbitals in Y3N@C80. These results enhance our understanding of the dynamics and molecular spin–orbit characteristics of clusterfullerenes, indicating their potential for multifunctional applications.

Extending the functional form of the methane PES in redundant coordinates for highly excited vibrational energy levels calculation

Potential energy surfaces (PES) of methanewhich are constructed using ten symmetrised combinations of four bond length and six interbond angles are referred to as (10S) PESs At high energy ranges, it was found that (10S) PESs permitted improving by factor of five the fit quality of ab initio electronic energies of methane versus standard nine symmetric coordinates (9S) PES representations both in internal, orthogonal or normal-mode coordinates. We extend predictions of vibrational band origins to spectral range above 10000 cm−1 to help future analyses of experimental spectra. Accuracy at high energies is increased without notable deterioration at low-E levels (rms deviation of 0.26 cm−1). Based on a comparison between various variants of (10S) PESs we expect that new theoretical band origins should have accuracy not worse than 1–3 cm−1 up to 13400 cm−1.

Single-shot LIBS: A rapid method for in situ and precise nutritional evaluation of hydroponic lettuce

Hydroponic farming has emerged as a promising method that can enable year around crop production, particularly in regions with non-arable land. Ensuring precise control over nutrient levels and growing conditions is imperative for optimizing crop quality and nutritional value. However, the existing state-of-the-art nutrient assessment methods demand tedious sample preparation and often prove to be either destructive or offline, lacking in options for in situ monitoring. Previous approaches to nutritional evaluation using laser-induced breakdown spectroscopy (LIBS) utilized multiple laser shots or labor-intensive sample preparation to achieve enhanced sensitivity. In this context, we propose a single-shot LIBS system with a custom-made optical collection unit coupled to spectrograph to improve sensitivity and reduce sample damage by employing low excitation energy levels (~ 1.5 mJ). This study demonstrates in situ nutrient monitoring of hydroponically grown lettuce leaves and roots using single-shot LIBS analysis, paving the way for enhanced crop cultivation practices and improved agricultural productivity. Additionally, we discuss energy optimization strategies aimed at improving sensitivity and achieving a high signal-to-background ratio, which are essential for effective and safe nutrient monitoring and analysis in hydroponic farming systems. The results and analysis reveal that highly reproducible and sensitive LIBS spectra can be obtained directly from lettuce plants without any prior sample preparation.Graphical

Optical thermometry using efficient upconversion luminescence in Er3+ self-sensitized NaYS2 under multi-wavelength excitation

Herein, a series of Er3+ self-sensitized NaYS2 phosphors are synthesized by the solid-gas reaction method for a novel upconversion luminescence thermometer. Er3+ possesses abundant excited state energy levels in the near-infrared region, enabling efficient upconversion luminescence by absorbing different near-infrared wavelength light. Compared to 980 nm excitation, the emission intensity is enhanced by nearly an order of magnitude under 1532 nm excitation, which can be attributed to the larger absorption cross-section of 4I13/2 and stronger absorption efficiency for Er3+. Based on the luminescence intensity ratio technique, the optical thermometry behaviors of NaYS2:Er3+ under different wavelength excitation are evaluated by employing the thermally coupled energy levels of 2H11/2/4S3/2. It can be deduced that the excitation wavelength has no significant effect on the temperature sensing parameters. Compared to other typical upconversion luminescence thermometers, NaYS2:Er3+ thermometer exhibits not only excellent sensitivity performance but also high upconversion luminescence efficiency, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing.

Benzimidazole based electron-transport hosts for efficient pure blue narrowband OLED device

Two electron-transport host materials are synthesized by linking anthracene with benzimidazole derivatives through a unit of methyl substituted phenyl. The methyl substitution generates a large dihedral angle between the benzimidazole plane and bridging phenyl, keeping the excited state distribution and energy levels of T1 and S1 unchanged. The electron-only devices reveal that the two hosts have obviously enhanced electron transport ability than that of Ph-AN-MBP without benzimidazole. As a result, the devices with Ph-AN-BIZ and N1-AN-BIZ as hosts and a blue multiple resonance material of tBuCz-DABNA as emitter exhibit high external quantum efficiency of 10.1 % and 9.1 %, respectively, and low turn-on voltage of 2.7 V, which is better than those of Ph-AN-MBP based device (7.9 %, 3.4 V). And their electroluminescence spectra have a very small full-width at half-maximum of 16.2 nm and pure blue color with CIE coordinates of (0.12, 0.11).

A note on degeneracy of excited energy levels in massless Dirac fermions

We propose a mechanism to construct the eigenvalues and eigenfunctions of the massless Dirac-Weyl equation in the presences of magnetic flux Φ localized in a restricted region of the plane. Using this mechanism we analyze the degeneracy of the existed energy levels. We find that the zero and first energy level has the same N+1 degeneracy, where N is the integer part of Φ2π. In addition, and contrary to what is described in the literature regarding graphene, we show that higher energy levels are N+m degenerate, being m the level of energy. In other words, this implies an indefinite growth of degenerate states as the energy level grows.

Ligand-mediate exciton allocation enables efficient cluster-based white light-emitting diodes via single and heavy doping

Despite potential in high-resolution and low-cost displays and lighting, multi-doping structures and low concentrations (<1%) limit repeatability and stability of single-emissive-layer white light-emitting devices. Herein, we report a singly doped white-emitting system of blue thermally activated delayed fluorescence host matrix (CzAcSF) doped by yellow Cu4I4 cluster ([tBCzDppy]2Cu4I4). CzAcSF:x% [tBCzDppy]2Cu4I4 films realize photo- and electro-luminescence colors from cool white to warm white at x = 20–40. The external quantum efficiency of 23.5% was achieved at x = 30, indicating the record-high efficiency among solution-processed analogs and the largest doping concentration among efficient white light-emitting devices. It shows that di(tert-butyl)carbazole moieties in [tBCzDppy]2Cu4I4 provide high-lying excited energy levels at~2.6 eV to mediate energy transfer from CzAcSF (2.9 eV) to coordinated Cu4I4 (2.2 eV). Our results demonstrate the antenna effect of ligands on optimizing charge and energy transfer in organic-cluster systems and superiority of white cluster light-emitting diodes in practical applications.

85‐3: Machine Learning Strategy Towards Inverse Design of Blue TADF Emitter: Training Excited State Properties Based on Density Functional Theory Calculations

We introduce inverse design strategy utilizing machine learning (ML) models to discover efficient blue thermally activated delayed fluorescence (TADF) organic emitter materials. Here, we leverage graph neural network (GNN) to predict the characteristic intrinsic materials properties of TADF such as excited state energy levels and their transition properties. The GNN model is trained based on density‐functional theory (DFT) calculation results to meet the TADF properties. We discuss consistency between experimental observation and ML predictions, and examined conditions for improving the accuracy of DFT calculations and ML models on top of it.

Control of the oscillation frequency of a vortex cluster in the trapped polariton condensate

An optically trapped exciton–polariton condensate forms states corresponding to excited energy levels of the confining potential. Recently, it was shown that non-uniformity of the ring-shaped trapping potential leads to the simultaneous occupation of two split energy levels. This results in the formation of an oscillating vortex cluster with periodically changing signs of topological charges. Here, we experimentally demonstrate the control of the topological charge oscillation frequency by tuning the ellipticity of the excitation profile. Our observations are corroborated using the linear Schrödinger equation for a two-dimensional quantum harmonic oscillator. Our findings open a promising avenue for the investigation of optical vorticity properties and their applications in controllable settings.

Novel Photocatalyst Based on Through‐Space Charge Transfer Induced Intersystem Crossing Enables Rapid and Efficient Polymerization Under Low‐Power Excitation Light

AbstractCurrently, most photoredox catalysis polymerization systems are limited by high excitation power, long polymerization time, or the requirement of electron donors due to the precise design of efficient photocatalysts still poses a great challenge. Herein, we propose a new approach: the creation of efficient photocatalysts having low ground state oxidation potentials and high excited state energy levels, along with through‐space charge transfer (TSCT) induced intersystem crossing (ISC) properties. A cabazole‐naphthalimide (NI) dyad (NI‐1) characterized by long triplet excited state lifetime (τT=62 μs), satisfactory ISC efficiency (ΦΔ=54.3 %) and powerful reduction capacity [Singlet: E1/2 (PC+1/*PC)=−1.93 eV, Triplet: E1/2 (PC+1/*PC)=−0.84 eV] was obtained. An efficient and rapid polymerization (83 % conversion of 1 mM monomer in 30 s) was observed under the conditions of without electron donor, low excitation power (10 mW cm−2) and low catalyst (NI‐1) loading (&lt;50 μM). In contrast, the conversion rate was lower at 29 % when the reference catalyst (NI‐4) was used for photopolymerization under the same conditions, demonstrating the advantage of the TSCT photocatalyst. Finally, the TSCT material was used as a photocatalyst in practical lithography for the first time, achieving pattern resolutions of up to 10 μm.

Curves of growth for transiting exocomets: Application to Fe II lines in the β Pictoris system

Using transit spectroscopy, exocomets are routinely observed in the young planetary system of β Pic. However, despite more than 35 yr of observations, we still have very little information on the physical properties and almost no information on the abundances of the gaseous clouds surrounding the comets’ nuclei, the difficulty being the conversion of the observed absorption profiles into column density measurements. Here, we present a new method to interpret the exocomet absorptions observed in β Pic spectrum and link them to the physical properties of the transiting cometary tails (e.g. size, temperature, and column density). We show that the absorption depth of a comet in a set of lines arising from similar excitation levels of a given chemical species follows a simple curve as a function of g·f, where f is the line oscillator strength and g its lower level multiplicity. This curve is the analogue of the curve of growth for interstellar absorption lines, where equivalent widths are replaced by absorption depths. To fit this exocomet curve of growth, we introduced a model where the cometary absorption is produced by a homogeneous cloud, covering only a limited fraction of the stellar disc. This model is defined by two parameters: α, characterising the size of the cloud relative to the star, and β, related to the optical depth of the absorbing gas. This model was tested on two comets observed with the Hubble Space Telescope in December 1997 and October 2018, in a set of lines of ionised iron (Fe II) at 2750 Å. The measured absorption depths are found to satisfactory match the two-parameter curve of growth model, indicating that both comets cover roughly 40% of the stellar disc (α = 0.4) and have optical thicknesses close to unity in those lines (β ~ 1). Then, we show that if we consider a set of lines arising from a wider range of energy levels, the absorbing species seems to be populated at thermodynamical equilibrium, causing the cometary absorption to follow a curve of growth as a function of g f ⋅ e−El/kBT (where T is the temperature of the absorbing medium). For the comet observed on December 6, 1997, we derive a temperature of T = 10 500 ± 500 K and a total Fe II column density of NFeII = (1.11 ± 0.09) × 1015 cm−2. By considering the departure from the Boltzmann distribution of the highest excited energy levels (El ~ 25 000 cm−1), we also estimate an electronic density of ne ≈ (3 ± 1) × 107 cm−3.

Optical and luminescent properties of Dy3+/Sm3+ doped and codoped Zinc Borophosphate glasses for W-LED application

In this work, a series of zinc borophosphate glasses (ZnPBAl), doped and codoped with Dy3+ and Sm3+, was studied for potential application in W-LEDs. The samples were prepared by the melt-quenching method and their luminescent and optical properties were investigated. The optical absorption spectra presented all Dy3+ and Sm3+ peaks corresponding to the transitions from the 6H15/2 and 6H5/2 states, respectively, to the excited energy levels. The 350 nm excitation source was chosen, considering photoluminescence excitation (PLE) results, to investigate the energy transfer from Dy3+ to Sm3+ ions. The energy transfer was indicated by photoluminescence (PL) spectra of Dy:Sm-codoped glasses and investigated by the energy transfer efficiency (η) using the lifetime data of both doped and codoped samples. The PL as a function of temperature was also studied. The CIE diagram of Dy-doped glasses showed their color emission close to the white region and the simulation of a combined Blue LED created an illumination route from warm to cold white light.

Molecular Design for Vertical Phase Distribution Modulation in High-Performance Organic Solar Cells.

Component distribution within the photoactive layer dictates the morphology and electronic structure and substantially influences the performance of organic solar cells (OSCs). In this study, a molecular design strategy is introduced to manipulate component and energetics distribution by adjusting side-chain polarity. Two non-fullerene acceptors (NFAs), ITIC-16F and ITIC-E, are synthesized by introducing different polar functional substituents onto the side chains of ITIC. The alterations result in different distribution tendencies in the bulk heterojunction film: ITIC-16F with intensified hydrophobicity aligns predominantly with the top surface, while ITIC-E with strong hydrophilicity gravitates toward the bottom. This divergence directly impacts the vertical distribution of the excitation energy levels, thereby influencing the excitation kinetics over extended time periods and larger spatial ranges including enhanced diffusion-mediated exciton dissociation and stimulated charge carrier transport. Benefitting from the favorable energy distribution, the device incorporating ITIC-E into the PBQx-TF:eC9-2Cl blend showcases an impressive power conversion efficiency of 19.4%. This work highlights side-chain polarity manipulation as a promising strategy for designing efficient NFA molecules and underscores the pivotal role of spatial energetics distribution in OSC performance.

Achieving Visible-Light-Excitable Blue TADF-Type Afterglow via Delicate Control of Excited States in Difluoroboron β-Diketonate Systems.

Blue afterglow constitutes of one of the primary afterglow colors and can convert into other afterglow colors through energy transfer. The reported studies show the fabrication of blue afterglow emitters, but most of them are formed by room-temperature phosphorescence mechanism and require UVB lights as excitation source (these high-energy lights may damage organic systems). Here we report visible-light-excitable blue thermally activated delayed fluorescence type (TADF-type) afterglow materials via delicate control of excited states in difluoroboron β-diketonate (BF2bdk) systems. Tiny change of the substituents in BF2bdk system has been found to pose significant influence on excited state energy levels and consequently narrow the singlet-triplet splitting energy of the system. As a result, both forward and reverse intersystem crossing have been accelerated, leading to the emergence of BF2bdk's TADF-type organic afterglow in rigid crystalline matrices. The resultant TADF-type afterglow materials exhibit emission lifetimes of several hundred milliseconds, photoluminescence quantum yield (PLQY) of 24.7 % and display temperature responsive property.

A step-by-step simulation code for estimating yields of water radiolysis species based on electron track-structure mode in the PHITS code

Objective. Time-dependent yields of chemical products resulting from water radiolysis play a great role in evaluating DNA damage response after exposure to ionizing radiation. Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo simulation code for radiation transport, which simulates atomic interactions originating from discrete energy levels of ionizations and electronic excitations as well as molecular excitations as physical stages. However, no chemical code for simulating water radiolysis products exists in the PHITS package. Approach. Here, we developed a chemical simulation code dedicated to the PHITS code, hereafter called PHITS-Chem code, which enables the calculation of the G values of water radiolysis species (•OH, eaq −, H2, H2O2 etc) by electron beams. Main results. The estimated G values during 1 μs are in agreement with the experimental ones and other simulations. This PHITS-Chem code also simulates the radiolysis in the presence of OH radical scavengers, such as tris(hydroxymethyl)aminomethane and dimethyl sulfoxide. Thank to this feature, the contributions of direct and indirect effects on DNA damage induction under various scavenging capacities can be analyzed. Significance. This chemical code coupled with PHITS could contribute to elucidating the mechanism of radiation effects by connecting physical, physicochemical, and chemical processes.

Unraveling the effect of aromaticity for the dynamics of excited states of single benzene fluorophores.

The photophysical properties of a series of recently synthesized single benzene fluorophores were investigated using ensemble density functional theory calculations. The energetic stability of the ground and excited state species were counterposed against the aromaticity index derived from local vibrational modes. It was found that the large Stokes shift of the fluorophores (up to ca. 5800 cm ) originates from the effect of electron donating and electron withdrawing substituents rather than -delocalization and related (anti-)aromaticity. On the basis of nonadiabatic molecular dynamics simulations, the absence of fluorescence from one of the regioisomers was explained by the occurrence of easily accessible S /S conical intersections below the vertical excitation energy level. It is demonstrated in the manuscript that the analysis of local mode force constants and the related aromaticity index represent a useful tool for the characterization of -delocalization effects in -conjugated compounds.

Efficient red thermally activated delayed fluorescence emitters achieved through precise control of excited state energy levels.

The variety of highly efficient red/near-infrared (NIR) materials with thermally activated delayed fluorescence (TADF) feature is extremely limited so far, and it is necessary to expand the candidate pool of excellent red/deep-red emitters. However, how to control the energy level alignment of the 1CT (singlet charge transfer) state and the 3LE (triplet local excitation) state to improve the emission efficiency of materials remains a challenge. Herein, based on our previously reported green fluorescent material 67dTPA-FQ, three new donor-acceptor type TADF materials (TQ-oMeOTPA, TsQ-oMeOTPA and SQ-oMeOTPA) were designed by introducing 4,4'-dimethoxy triphenylamine (MeOTPA) as the donor, and introduced S atoms on the acceptors to enhance the spin-orbit coupling (SOC) and CT effects. The theoretical calculations showed that the newly introduced MeOTPA and S atom successfully enhanced the CT effect of the materials, not only shifting the luminescence peak to the deep red region but also effectively adjusting the energy level alignment of the excited state, accelerating the reverse intersystem crossing process. Finally, the organic light-emitting diodes based on SQ-oMeOTPA exhibit an external quantum efficiency of 19.1%, with an emission peak at 619 nm. This work not only expands the candidate inventory of red TADF materials, but also proves the feasibility of designing emitters by adjusting the excited state energy levels, greatly broadening the diversity of TADF emitters in design, and providing a powerful means for rapidly screening efficient emitters in the future.

1,1'-Bis-(diphenylphosphino)ferrocene appended d8- and d10-configuration based thiosquarates: the molecular and electronic configurational insights into their sensitization and co-sensitization properties for dye sensitized solar cells.

Three new d8- and d10-configuration based 1,1'-bis-(diphenylphosphino)ferrocene (dppf) appended thiosquarates complexes with general composition [M(mtsq)2dppf] (M = Ni2+ (NiL2); Zn2+ (ZnL2) and Cd2+ (CdL2)) (mtsq = 3-ethoxycyclobutenedione-4-thiolate) have been synthesized and characterized spectroscopically as well as in case of NiL2 by single crystal X-ray diffraction technique. The single crystal X-ray analysis reveals square planar geometry around Ni(II) in NiL2, where Ni(II) coordinates with two sulfur centres of two mtsq ligands in monodentate fashion and two phosphorus of a dppf ligand in chelating mode. The supramolecular architecture of NiL2 is sustained by intermolecular C-H⋯O interactions to form one-dimensional chain. Further, the application of these newly synthesized complexes as sensitizers and co-sensitizers/co-absorbents with ruthenium based N719 sensitizer in dye-sensitized solar cells (DSSCs) have been explored. The DSSC set-up based on NiL2 offers best photovoltaic performance with photovoltaic efficiency (η) 5.12%, short-circuit current (Jsc) 11.60 mA cm-2, open circuit potential (Voc) 0.690 V and incident photon to current conversion efficiency (IPCE) 63%. In co-sensitized DSSC set-up, ZnL2 along with state-of-the-art N719 dye displays best photovoltaic performance with η 6.65%, Jsc 14.47 mA cm-2, Voc 0.729 V and IPCE 69%, thereby showing an improvement by 15.25% in photovoltaic efficiency in comparison to the photovoltaic efficiency of N719 sensitized DSSC set-up. Variation in co-sensitization behaviour have been ascribed to the differences in the excited state energy level of co-sensitizers. The ZnL2 and CdL2 have a higher energy level position than N719 dye, allowing efficient electron transfer to N719 during light irradiation, while excited state of NiL2 is lower than N719 dye, preventing photoexcited electron transfer to N719, resulting in its lowest overall efficiency among the three co-sensitized DSSC setups.

Modulatory spin-flip of triplet excitons via diversiform electron-donating units for MR-TADF emitters towards solution-processed narrowband OLEDs.

Multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules are emerging as promising candidates for high-resolution organic light-emitting diode (OLED) displays, but MR-TADF emitters always suffer from an unsatisfactory rate constant of reverse intersystem crossing (k RISC) due to inherently low spin orbital coupling strength between excited singlet and triplet states. Herein, we systematically investigate the long-range charge transfer (LRCT) and heavy-atom effects on modulating the excited state natures and energy levels via integrating diversiform electron-donating units with the MR skeleton. Compared with unsubstituted analogues, newly designed MR-TADF emitters exhibit significantly boosted k RISC values and close-to-unity photoluminescence quantum yield especially for tBuCzBN-PXZ (2.5 × 105 s-1) and tBuCzBN-Ph-PSeZ (2.1 × 105 s-1). Leveraging these exceptional properties, the maximum external quantum efficiency values of tBuCzBN-PXZ- and tBuCzBN-Ph-PSeZ-based solution-processed OLEDs can reach 21.3% and 19.4%, which are in the first tier of reported solution-processed MR-TADF binary OLEDs without employing additional sensitizers. This study provides a framework for modulating photoelectrical properties of MR-TADF emitters through fastidiously regulating LRCT and heavy-atom effects.

Precise molecular engineering for the preparation of pyridinium photosensitizers with efficient ROS generation and photothermal conversion.

Organic photosensitizers (PSs) with aggregation-induced emission properties have great development potential in the integrated application of multi-mode diagnosis and treatment of photodynamic therapy (PDT) and photothermal therapy (PTT). However, preparing high-quality PSs with both optical and biological properties, high reactive oxygen species (ROS) and photothermal conversion ability are undoubtedly a great challenge. In this work, a series of pyridinium AIE PSs modified with benzophenone have been synthesized. A wide wavelength range of fluorescent materials was obtained by changing the conjugation and donor-acceptor strength. TPAPs5 has a significant advantage over similar compounds, and we have also identified the causes of high ROS generation and high photothermal conversion in terms of natural transition orbitals, excited state energy levels, ground-excited state configuration differences and recombination energy. Interestingly, migration of target sites was also found in biological imaging experiments, which also provided ideas for the design of double-targeted fluorescent probes. Therefore, the present work proposed an effective molecular design strategy for synergistic PDT and PTT therapy.