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The strategy of designing efficient room-temperature phosphorescence (RTP) emitters based on hydrogen bond interactions has attracted great attention in recent years. However, the regulation mechanism of the hydrogen bond on the RTP property remains unclear, and corresponding theoretical investigations are highly desired. Herein, the structure–property relationship and the internal mechanism of the hydrogen bond effect in regulating the RTP property are studied through the combination of quantum mechanics and molecular mechanics methods (QM/MM) coupled with the thermal vibration correlation function method. Intermolecular interactions, excited-state transition properties, reorganization energies, radiative and nonradiative decay rates, and the intersystem crossing rates are analyzed in detail. Results show that intermolecular hydrogen bonds can effectively delocalize molecular orbitals, enhance spin–orbit coupling (SOC) effect, and thus accelerate intersystem crossing (ISC) processes. In addition, an intermolecular hydrogen bond can also suppress nonradiative transition by restricting molecular motion, thereby promoting generation of phosphorescence. However, an excessively enhanced intermolecular hydrogen bond effect promotes molecular vibrations, leading to increased reorganization energies and thus facilitating nonradiative energy consumption process. The hydrogen bond “double-edged sword” effect on RTP properties and nonradiative decay process is theoretically revealed. Therefore, reasonable control of the hydrogen bond strength is beneficial for the development of efficient RTP emitters. Our research provides rational explanations for previous measurements and highlights the hydrogen bond effect in constructing efficient RTP emitters.

Quantum and quasi-classical dynamics calculations were conducted for the reaction of Si with OH on the latest potential energy surface (PES), which is obtained by fitting tens of thousands of ab initioenergy points by using the many-body expansion formula. To obtain an accurate PES, all energy points calculated with aug-cc-pVQZ and aug-cc-pV5Z basis sets were extrapolated to the complete basis set limit. The accuracy of our new PES was verified by comparing the topographic characteristics and contour maps of potential energy with other works. In addition, the anharmonic vibrational frequencies of HOSi and HSiO based on the present ab initioand PES by means of quantum dynamics methods were calculated. Dynamics information such as reaction probability, integral cross sections (ICS), product distribution, and rate constants was obtained on the new HOSi(X2A′) PES. The dynamic information calculated using the quasi-classical trajectory method and time-dependent wave packet method is generally in good agreement, except for the vibrational state-resolved ICSs of product. The calculated differential cross section and capture time reveal that the reaction is primarily governed by the complex formation mechanism.

Organic solid-state lasers have received increasing attention due to their great potential for realizing organic continuous-wave or electrically driven lasers. Moreover, they exhibit significant promise for optoelectronic devices due to their chemically tunable optoelectronic properties and cost-effective self-assembly traits. Recently, a great progress has been made in organic solid-state lasers via spatially separated charge injection and lasing. However, making directly electrically driven organic semiconductor lasers is very challenging. It is difficult because of a number of excitonic losses caused by the spin-forbidden nature as well as serious efficiency roll-off at a high current density. Here, a multifunction gain material, functioning both as a thermally activated delayed fluorescence (TADF) emitter with exceptional optical gain and as a source of phosphorescence, was theoretically investigated. The new molecule we designed exhibits a reduction of triplet accumulation through an effective exciton radiative process (5-fold boost in figure of merit) and significantly decreased exciton binding energy (dipole moment from 5.77 to 14.03 D), which benefit amplified spontaneous emission and lasing emission. Our work provides theoretical insights into organic solid-state lasers and may contribute to the development of new and efficient laser-gaining molecules.

As a typical thermally activated delayed fluorescence (TADF) emitter with green emission, 4CzIPN has attracted much attention recently. Most studies indicated that 4CzIPN doped in different hosts presented different performances; thus, the hosts should have an obvious influence on its photophysical properties. Herein, the influence of four kinds of hosts, including m-CzPym, m-CzTrz, p-CzPym, and p-CzTrz, on the photophysical properties of 4CzIPN is investigated. Molecular dynamics simulations were performed to simulate the host–guest conformations, and the photophysical properties were studied using the combined quantum mechanics/molecular mechanics method coupled with the thermal-vibration correlation function method. It is found that 4CzIPN in doped films has larger transition dipole moments and spin–orbital coupling constants compared to that in nondoped films. Faster radiative decay, intersystem crossing rates, and higher fluorescence efficiency could be obtained in doped films. Our work helps to better understand the photophysical properties of 4CzIPN in doped films and may favor the design of new hosts.

Organic room-temperature phosphorescence (RTP) emitters with long lifetimes, high exciton utilizations, and tunable emission properties show promising applications in organic light-emitting diodes (OLEDs) and biomedical fields. Their excited-state properties are highly related to single molecular structure, aggregation morphology, and external stimulus (such as hydrostatic pressure effect). To gain a deeper understanding and effectively regulate the key factors of luminescent efficiency and lifetime for RTP emitters, we employ the thermal vibration correlation function (TVCF) theory coupled with quantum mechanics/molecular mechanics (QM/MM) calculations to investigate the photophysical properties of three reported RTP crystals (Bp-OEt, Xan-OEt, and Xan-OMe) with elastic/plastic deformation. By analyzing the geometric structures and stacking modes of these crystals, we observe that the geometric structure variations influence the electronic structures, subsequently modifying the transition properties and the energy consumption processes. Specifically, the presence of strong π–π interactions and hydrogen bonds in the Xan-OEt crystal inhibits a nonradiative decay process, thereby realizing long-lived emission. Additionally, the hybridized local and charge-transfer (HLCT) excited-state feature with the largest charge transfer excitation contributions (57.74%) for Xan-OEt stabilizes the triplet excitons and facilitates the radiative decay process, ultimately achieving high efficiency and long lifetime emissions. Furthermore, by applying high hydrostatic pressure for the Bp-OEt crystal, the RTP emission efficiencies and lifetimes are enhanced and blue-shifted. All of these results demonstrate the crucial role of molecular structure and stacking modes as well as the hydrostatic pressure effect in regulating RTP properties. Thus, our findings reveal the structure-packing-property relationship and highlight the control of molecular packing and the related tunable approaches, which could provide prospective strategies for constructing stimuli-responsive RTP emitters in practical applications.

Multifunctional thermally activated delayed fluorescence (TADF) molecules have recently attracted great attention. The light-emitting mechanisms of the TADF molecule PTZ-AQ with aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) in three different aggregation states are studied using the combined quantum mechanics and molecular mechanics (QM/MM) method as well as the thermal vibration correlation function method. It is found that different aggregation patterns would induce different intermolecular interaction and molecular geometries. The different energy diagram of excited states also induce variation of emission colors and (reverse) intersystem crossing processes. By comparing with the light-emitting properties in solvent, the AIE property is confirmed, which is induced by enhanced radiative rate and decreased nonradiative rates in aggregation. The bicolor switch mechanism for the molecule in the solid state should have a close relationship with the dihedral angle change between the donor and the acceptor. The calculation results provide valuable information for understanding the light-emitting mechanism of the PTZ-AQ based polymorphs with AIE and MCL properties, which would favor the design of a new type multifunctional TADF molecules.

A full three-dimensional global potential energy surface (PES), covering the whole configuration space, is reported first for the title system by fitting high-level ab initioenergies at the multireference configuration interaction level with the aug-cc-pV6Z basis set. In this work, the many-body expansion method is invoked to fit the innate character of the CH2+(12A″) PES. The topographical features are examined in detail based on the new global PES and in accordance with the other calculations from the ab initioenergies, which show the correct behavior at the C+(2P) + H2(X1Σg+) and CH+(a3Π) + H(2S) dissociation limits. Using a time-dependent wave packet method, we provide insights into the dynamics behavior for reaction of C+(2P) + H2(X1Σg+) → CH+(a3Π) + H(2S). The integral cross sections and reaction probabilities increase monotonically in terms of the collision energy.

We proposed a passively stabilized Q-switched Er:Lu_2O_3 laser at 2845 nm, applying a MXene Nb_2CT_x nanosheets saturable absorber prepared by the liquid-phase exfoliation method. The surface morphology and nonlinear properties of this nanosheet were systematically characterized. Average output power of 542 mW for the Q-switched laser was obtained under 7.26 W of absorbed pump power. Meanwhile, the Q-switched pulse duration was measured to be 223.7 ns with 142.9 kHz repetition rate corresponding to a peak power of 16.96 W.

The development of efficient sky-blue thermally activated delayed fluorescence (TADF) emitters is highly desired. However, the types and amounts of sky-blue TADF are far from meeting the requirements, and effective molecular design strategies are expected. Herein, the photophysical properties and excited-state dynamics of 12 molecules are theoretically studied based on the thermal vibration correlation function method. Distributions of holes and electrons are analyzed by the heat maps. The frontier molecular orbital distribution, adiabatic singlet-triplet energy gap, and reorganization energy are analyzed in detail. Furthermore, the radiative and non-radiative as well as the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes are studied, and the up-conversion process is illustrated. Our results indicate that different substitution positions and numbers play an important role in the luminescence properties of TADF molecules. The meta-position substitutions restrict the geometry variations, hinder the non-radiative energy consumption process, and promote the radiative process of TADF molecules. Meanwhile, molecules with ortho-position substitutions possess the smallest energy gaps (ΔEst) and the largest RISC rates. Moreover, molecules with the substitutions of one tBCz group and two PO groups have the smallest ΔEstand the largest spin orbital coupling. Thus, a wise molecular design strategy, namely, ortho-position substitutions as well as substitutions with one tBCz group and two PO groups, is proposed to facilitate the RISC process. Based on this rule, new efficient TADF molecules are theoretically designed and proposed. Our work reasonably elucidates the experimental measurements, and the effects of different substitution numbers and positions of secondary acceptors on TADF properties are highlighted, which could provide a theoretical perspective for designing efficient sky-blue TADF molecules.

Abstract: Potamogeton crispushas a significant effect on the purification of contaminated water and can improve the stability of aquatic ecosystems, but much research work was carried out under controlled conditions. The water quality indexes were measured to determine whether the purification effect under natural conditions can achieve the same effect as under controlled conditions in this study. The physical and chemical indicators of the water around the P. crispuspopulation were monitored to study the range of impact of P. crispuspopulation during the logarithmic growth period on the water in Xuanwu Lake, Nanjing City. These indicators included pH, secchi disc transparency, turbidity, dissolved oxygen, total nitrogen, ammonia, and total phosphate. The result showed that P. crispuspopulation played an important role in improving lake water quality. P. crispuspopulation increased dissolved oxygen concentration, improved transparency, reduced turbidity, absorbed nutrients from the water column. The transparency, turbidity, and pH value could be affected to 40% of the width of P. crispuspopulation, while dissolved oxygen concentration could be affected to the same width of the population. But the nitrogen and phosphorus concentration could be affected to 10% of the population. In vertical space, the influence of P. crispuspopulation on the surface water was greater than that of the bottom water. According to this study, the gap between P. crispuspopulation can be controlled at 20% of the population width, which can effectively reduce nutrient concentration, improve water transparency and dissolved oxygen content, improve water quality. In the process of ecological restoration with P. crispuspopulation, the width of P. crispuspopulation should be controlled and prevent the spread by regular harvesting, blocking with the net, and so on. The gap between populations should also be determined according to the population width.

Employing dual-emission thermally activated delayed fluorescence (TADF) molecules to fabricate single emitters in highly efficient white organic light-emitting diodes (WOLEDs) is still a challenge. In this work, a systematic study on the luminescence mechanism of three TADF molecules with blue–orange dual emission is performed. It is found that the quasi-axial (ax) conformer is responsible for blue normal fluorescence (NF), while the quasi-equatorial (eq) conformer is responsible for orange TADF. In addition, the upconversion for the TADF molecules happens from the first triplet state (T1) and the second triplet state (T2) to the first singlet state (S1) in the quasi-equatorial conformers. In addition, the transition from T1to S1and T2to S1also happens in the process of conformation transformation. Besides, our study also indicates that the donor with an asymmetric bond length in the six-membered ring could favor the generation of dual conformations and dual emission. Some molecules with PTZ or PXZ as donors are predicted as potential emitters with white light emission. Our research would favor the design of TADF emitters with dual emission in WOLEDs.

As the new type of organic photoelectric device, circularly polarized thermally activated delayed fluorescence (CP-TADF) organic light-emitting diodes (OLEDs) with the advantages of high exciton utilization and full color saturation show wide applications in 3D display, encrypted information storage and quantum computing. However, due to the conflict between high luminescence efficiency and large luminescence asymmetry factor (glum), the species of efficient CP-TADF molecules are limited. Herein, theoretical studies are performed by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods coupled with thermal vibration correlation function, the effects of different acceptors on circularly polarized luminescence (CPL) and TADF properties are investigated, inner mechanisms between basic molecular structures and luminescence properties are revealed. By calculating intersystem crossing rate, reverse intersystem crossing rate, radiative decay rate and non-radiative decay rate, we determine that the SPHCN molecule exhibited dominate TADF properties. Additionally, the electronic circular dichroism (ECD) spectrum and glumvalues are quantitatively calculated to measure the CPL properties. Based on our findings, we conclude that lengthening the acceptor unit is a feasible strategy for improving the luminescence properties of CP-TADF molecules. Our study provides a novel approach for understanding the molecular luminescence mechanism of CP-TADF, which could promote the development of CP-OLEDs.

The interaction of exciton-plasmon coupling and the conversion of exciton-plasmon-photon have been widely investigated experimentally and theoretically. In this review, we introduce the exciton-plasmon interaction from basic principle to applications. There are two kinds of exciton-plasmon coupling, which demonstrate different optical properties. The strong exciton-plasmon coupling results in two new mixed states of light and matter separated energetically by a Rabi splitting that exhibits a characteristic anticrossing behavior of the exciton-LSP energy tuning. Compared to strong coupling, such as surface-enhanced Raman scattering, surface plasmon (SP)-enhanced absorption, enhanced fluorescence, or fluorescence quenching, there is no perturbation between wave functions; the interaction here is called the weak coupling. SP resonance (SPR) arises from the collective oscillation induced by the electromagnetic field of light and can be used for investigating the interaction between light and matter beyond the diffraction limit. The study on the interaction between SPR and exaction has drawn wide attention since its discovery not only due to its contribution in deepening and broadening the understanding of SPR but also its contribution to its application in light-emitting diodes, solar cells, low threshold laser, biomedical detection, quantum information processing, and so on.

Purely organic room temperature phosphorescence (RTP) materials have garnered extensive attentions in anti-counterfeiting and encryption, information display, biological imaging and organic light emitting diodes (OLEDs) due to the features of long lifetimes, low toxicity and good biocompatibility. Nevertheless, both the species and amounts of the efficient RTP molecules are far from meeting the requirements for practical applications, and the quantitative relationship between molecular structures and optoelectronic properties needs full elucidated. Herein, the photophysical properties and properties of three isomers (o-BA, m-BA and p-BA) are explored based on the first-principles calculations coupled with thermal vibration correlation function (TVCF) method and kinetic Monte Carlo simulations. The substituent effects on the molecular structures, intermolecular interactions, transition properties, Huang-Rhys factors and reorganization energies, excited state dynamics as well as transfer integrals and charge carrier mobilities are investigated in detail to clarify the structure-property relationships. Results show that o-BA achieves fast radiative rate on account of impressive transition dipole moment and oscillator strength, but equally large non-radiative decay rate leads to low RTP efficiency. Promisingly, the highest holes mobility is determined for o-BA due to the largest transfer integrals of holes originating from the strong intermolecular interactions. In addition, compared with o-BA and p-BA, m-BA could achieve fast intersystem crossing (ISC) rate with large spin orbit coupling constant and low non-radiative decay rate with small geometric structure changes. Relatively balanced holes and electrons mobilities of m-BA have been demonstrated, which contributes to the recombination of excitons and the improvement of luminescence efficiency. For p-BA, the strong intermolecular hydrogen bonding restricts the free rotation of single bonds and promotes the molecular coplanarity, which contributes to efficient emission. Furthermore, the charge mobility is calculated and the temperature dependence is investigated, the hopping mechanisms for studied isomers are illustrated. This work reveals the relationship among molecular structures, crystal packing modes, photophysical properties and charge transport properties of isomers, and provides an insight for molecular design and property prediction.

We present a hybrid waveguide-magnetic resonance system with split ring resonators (SRRs) periodically arranged on top of a waveguide layer. Due to the destructive interference between the electric coupling to the magnetic resonance mode generated in the SRRs and the TE/TM waveguide modes supported by the waveguide layer, double plasmon-induced transparency is obtained at the infrared wavelength. Furthermore, the PIT resonance can be dynamically tuned by the incident angle. An ultranarrow PIT window with an FWHM of 7 nm is observed at the wavelength of 1.448 μm. The group index at the narrow PIT window can reach up to 100. We also demonstrate that the refractive index sensitivity and the figure of merit value can reach up to 640  nm/RIU and 64 in the sensing range, respectively. The proposed hybrid waveguide-magnetic resonance system with a high-quality factor PIT window is promising for efficient optical sensing, optical switching, and slow-light device design.

Directly measuring thermal focal length is important for designing and optimizing the mode-locking oscillator, especially for a 2 μm mode-locking laser. In this paper, we propose a novel interferometric method for measuring the thermal focal length in a 2 μm mode-locking laser. This method provides a precise measurement of the thermal focal length inside a long-folded oscillator in both lasing and non-lasing operation. We also theoretically calculate the thermal focal length based on the temperature distribution inside the laser crystal, which matches well with the experimental results.

We propose a high-power, noise-like pulse (NLP), Tm-doped fiber oscillator applying the nonlinear polarization rotation method. The repetition rate is 12.94 MHz resulting in a pulse energy of 75.7 nJ. The emitted mode-locking spectrum can be tuned from 1885 nm to 1949 nm in a 64 nm spectral range. A theoretical model is built to illustrate the NLP dynamics and its boundary conditions with a soliton pulse inside the 2 ?m fiber ring cavity. The corresponding simulation results match well with our experimental results.

We observe a strong self-pulsing phenomenon in an all-fiber Er-doped ring laser. With an increase in the pump power, the generated pulse gradually evolves from a sine-wave pulse to a typical mode-locking pulse train. The self-mode-locked laser pulse obtained has a pulse-repetition rate in the megahertz region and a maximum average output power of around 1 mW. The self-pulsing evolving dynamics can be analyzed using coupled-wave rate equations by simultaneously considering the interaction of two adjacent Er-ions and the reabsorption loss of the ground-state energy levels.