Structural identification of single boron-doped graphdiynes by computational XPS and NEXAFS spectroscopy.

Boron-doped graphdiyne (B-GDY) material exhibits an excellent performance in electrocatalysis, ion transport, and energy storage. However, accurately identifying the structures of B-GDY in experiments remains a challenge, hindering further selection of suitable structures with the most ideal performance for various practical applications. In the present work, we employed density functional theory (DFT) to simulate the X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectra of pristine graphdiyne (GDY) and six representative single boron-doped graphdiynes at the B and C K-edges to establish the structure-spectroscopy relationship. A notable disparity in the C 1s ionization potentials (IPs) between substituted and adsorbed structures is observed upon doping with a boron atom. By analyzing the C and B 1s NEXAFS spectra on energy positions, spectral widths, spectral intensities, and different spectral profiles, we found that the six single boron-doped graphdiyne configurations can be sensitively identified. Moreover, this study provides a reliable theoretical reference for distinguishing different single boron-doped graphdiyne structures, enabling accurate selection of B-GDY structures for diverse practical applications.

Modulation of luminescence properties of circularly polarized thermally activated delayed fluorescence molecules with axial chirality by donor engineering.

Multifunctional thermally activated delayed fluorescence (TADF) materials are currently a trending research subject for luminescence layer materials of organic light-emitting diodes (OLEDs). Among these, circularly polarized thermally activated delayed fluorescence (CP-TADF) materials have the advantage of being able to directly achieve highly efficient circularly polarized luminescence (CPL). The simultaneous integration of outstanding luminescence efficiency and excellent luminescence asymmetry factor (glum) is a major constraint for the development of CP-TADF materials. Therefore, on the basis of first-principles calculations in conjunction with the thermal vibration correlation function (TVCF) method, we study CP-TADF molecules with different donors to explore the feasibility of using the donor substitution strategy for optimizing the CPL and TADF properties. The results indicate that molecules with the phenothiazine (PTZ) unit as the donor possess small energy difference, a great spin-orbit coupling constant and a rapid reverse intersystem crossing rate, which endow them with remarkable TADF features. Meanwhile, compared with the reported molecules, the three designed molecules exhibit better CPL properties with higher glum values. Effective molecular design strategies by donor engineering to modulate the CPL and TADF properties are theoretically proposed. Our findings reveal the relationship between molecular structures and luminescence properties of CP-TADF molecules and further provide theoretical design strategies for optimizing the CPL and TADF properties.

Theoretical design and performance prediction of deep red/near-infrared thermally activated delayed fluorescence molecules with through space charge transfer.

Thermally activated delayed fluorescence (TADF) molecules with through-space charge transfer (TSCT) have attracted much attention in recent years because of their ability to simultaneously reduce the energy difference (ΔEST) and enlarge the spin-orbit coupling (SOC). In this paper, 40 molecules are theoretically designed by changing the different substitution positions of the donors and acceptors, and systematically investigated based on the first-principles calculations and excited-state dynamics study. It is found that the emission wavelengths of v-shaped molecules with intramolecular TSCT are larger than those of the molecules without TSCT. Therefore, the intramolecular TSCT can induce the red-shift of the emission and realize the deep-red/near-infrared emission. Besides intramolecular TSCT can simultaneously increase the SOC as well as the oscillator strength and reduce the ΔEST. In addition, PXZ or PTZ can also favor the realization of smaller ΔEST and red-shift emission. Our calculations suggest that intramolecular TSCT and suitable donors (-PXZ or -PTZ) are an effective strategy for the design of efficient deep red/near-infrared TADF emitters.

Role of Bridging Groups in Regulating the Luminescence and Charge Transfer Properties of Thermally Activated Delayed Fluorescence Molecules: A Theoretical Perspective.

Organic emitters with a simultaneous combination of aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) characteristics are in great demand due to their excellent comprehensive performances toward efficient organic light-emitting diodes (OLEDs), biomedical imaging, and the telecommunications field. However, the development of efficient AIE-TADF materials remains a substantial challenge. In this work, light-emitting properties of two AIE-TADF molecules with different bridging groups ICz-BP and ICz-DPS are theoretically investigated in the solid state with the combined quantum mechanics/molecular mechanics (QM/MM) method and the thermal vibration correlation function (TVCF) theory. The research indicates that the C═O bridging bond in ICz-BP is more favorable than the S═O bridging bond in ICz-DPS for enhancing the planarity of the acceptor, increasing conjugation, and thereby elevating the transition dipole moment density. Simultaneously, the stacking pattern of ICz-BP in the solid facilitates a reduction in energy gap between S1 and T1 (ΔEST), achieving rapid reverse intersystem crossing rate (kRISC). Furthermore, compared to toluene, the stacking patterns of ICz-BP and ICz-DPS in the solid effectively suppress the out-of-plane wagging vibration of the acceptor, thereby inhibiting the loss of nonradiative energy in the excited state and realizing aggregation-induced emission. Moreover, the charge transport properties of both electrons and holes in ICz-BP are found to be higher than the corresponding rates in ICz-DPS, attributed to the smaller internal reorganization energy of ICz-BP in the solid state. Additionally, the calculations reveal a more balanced charge transport characteristic in ICz-BP, contributing to efficient exciton recombination and emission and ultimately mitigating efficiency roll-off. Based on these computational results, we aim to unveil the relationship between molecular structure and light-emitting properties, aiding in the design and development of efficient AIE-TADF devices.

Theoretical Insights into the Photophysical Properties of 4CzIPN Doped in Different Hosts: A Multiscale Study.

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.

Highly Efficient Luminescence from a Red Thermally Activated Delayed Fluorescence Emitter with Flexible Conformation of Ancillary Groups.

Robust scaffolds were typically applied in thermally activated delayed fluorescence (TADF) molecules to suppress the non-radiative decay, trigger the fast spin-flipping, and enhance the light out-coupling efficiency. Herein, we disclosed for the first time the positive effect of flexible conformation of ancillary groups on the photophysical properties of TADF emitter. The red TADF emitter Ph-TPA with flexible conformation demonstrated small excited-state structural distortion and low reorganization energy compared to the counterpart Mc-TPA with a rigid macrocycle. Consequently, Ph-TPA showed an excellent photoluminescent quantum yield (PLQY) of 92 % and a state-of-the-art external quantum efficiency (EQE) of 30.6 % at 630 nm. This work could deepen our understanding of structure-property relationships of organic luminophores and help us to rationalize the design of efficient TADF materials.

First-principles studies on the electronic and photocatalytic water splitting properties of surface functionalized Y2C-based MXenes.

Recently, MXenes, an emerging family of two-dimensional (2D) materials, have attracted increasing interest for photocatalytic water splitting due to their various excellent physical and chemical properties, such as large specific surface area, good hydrophilicity, and remarkable light absorption ability. However, the photocatalysts of MXenes with symmetric structures are limited by rapid recombination of photo-generated carriers and the prerequisite of a large band gap no less than 1.23 eV. Differently, Janus MXenes with different surface functional groups facilitate the separation of photo-generated electrons and holes with the help of the intrinsic electric field. And, at the same time, there is no prerequisite for the band gap of Janus MXene photocatalysts as long as they possess appropriate band edge positions. Here, we explored the structural, electronic and photocatalytic water splitting properties of symmetric Y2CT2 and Janus Y2CTT' MXenes (T, T' = H, F, Cl, OH) using the density functional theory (DFT) method. Our calculations show that all the investigated Y2CT2 are not suitable photocatalysts for photocatalytic water splitting at all pH values (pH = 0, 7, and 14). In contrast, all the investigated Janus Y2CTT' MXenes are good water splitting photocatalysts with high optical absorption coefficients and remarkable solar-to-hydrogen (STH) efficiencies larger than 18% at pH = 14. Moreover, the STH efficiencies are larger than 18% even at all investigated pH values for Y2CHCl (18.5-22.6%), Y2 CFCl (∼18.7%), and Y2 C(OH)Cl (∼19.4%). Based on the first-principles calculations, we here for the first time propose an easy strategy to design Janus MXene photocatalyst candidates with possible high STH efficiency according to the electronic properties of their symmetric counterparts. Our study is helpful for the future design of Janus MXenes and more generally Janus 2D photocatalysts for water splitting with high STH efficiency.

Mechanically controllable conductance in carbon nanotube based nanowires.

Carbon nanotubes (CNTs) are considered to be promising candidates for fabricating nanowires, due to their stable quasi-one-dimensional structure. Controlling the electronic transport properties is one of the most vital issues for molecular nanowires. Herein, using density functional theory combined with nonequilibrium Green's function method, we systematically investigate the current evolution of (4, 4) single-walled CNT based nanowires in squashing processes. When the CNTs are squashed by applying different pressure along the radial direction, a negative correlation can be found between the electrical conductance of the nanowire and the pressure. Besides, the response of the nano junction current to pressure is influenced by the squashing direction. Not only does the geometric structure show symmetry breaking in the specific squashing direction, which causes the CNT electrodes to change from conductors to semiconductors, but also obvious π stacking behavior can be witnessed in this squashing direction. More intriguingly, because the current of the nano junction can be completely cut off by squashing the CNTs, a significant switching behavior with the on/off ratio of up to 103 is obtained at low bias voltages. The underlying mechanisms for these phenomena are revealed by the analysis of the band structures, transmission spectra, frontier molecular orbitals and transmission pathways. These electronic transport properties make CNT a promising candidate for realizing conductance controllable nano devices.

Theoretical exploration of the bromine substitution effect and hydrostatic pressure responsive mechanism for room temperature phosphorescence.

Stimulus-responsive organic room temperature phosphorescence (RTP) materials with long lifetimes, high efficiencies and tunable emission properties have broad applications. However, the amounts and species of efficient RTP materials are far from meeting the requirements and the inner stimulus-responsive mechanisms are unclear. Therefore, developing efficient stimulus-responsive RTP materials is highly desired and the relationship between the molecular structures and luminescent properties of RTP materials needs to be clarified. Based on this point, the influences of different substitution sites of Br on the luminescent properties of RTP molecules are studied by the combined quantum mechanics and molecular mechanics (QM/MM) coupled with thermal vibration correlation function (TVCF) theory. Moreover, the hydrostatic pressure effect on the efficiencies and lifetimes is explored and the inner mechanism is illustrated. The results show that, for the exciton conversion process, the o-substitution molecule possesses the largest spin-orbit coupling (SOC) value (〈S1|Hso|T1〉) in the intersystem crossing (ISC) process and this is conducive to the accumulation of triplet excitons. However, for the energy consumption process, the large SOC value (〈S0|Hso|T1〉) for the p-substitution molecule brings a fast non-radiative decay rate, and the small SOC value for the m-substitution molecule generates a decreased non-radiative decay rate which is helpful for realizing long lifetime emission. Keeping with this perspective, the conflict between high exciton utilization and long RTP emission needs to be balanced rather than enhancing the SOC effect by simply adding heavy atoms in RTP systems. Through regulating the molecular stacking modes by the hydrostatic pressure effect, the inner stimulus-responsive mechanism is revealed. The data of 〈S1|Hso|T1〉 in the ISC process remain almost unchanged, while 〈S0|Hso|T1〉 values and transition dipole moments are sensitive to the hydrostatic pressure. Under 1 GPa, the RTP molecule achieves a maximum efficiency (81.17%) and long lifetime (2.72 ms) with the smallest SOC and decreased non-radiative decay rate. To our knowledge, this is the first time that the hydrostatic pressure responsive mechanism for RTP molecules is revealed from a theoretical perspective, and the relationships between molecular structures and luminescent properties are detected. Our work could facilitate the development of high performance RTP molecules and expand their applications in multilevel information encryption.

Interfacial electronic properties between PtSe2 and 2D metal electrodes: a first-principles simulation.

Monolayer (ML) PtSe2 is a two-dimensional (2D) semiconductor with a modest band gap and high carrier mobility, and it is a promising 2D material for electronic devices. Finding suitable metal electrodes is a key factor in fabricating high-performance PtSe2 field effect transistors (FETs). In this study, a series of 2D metals, transition metal dichalcogenides (NbSe2, TaS2), borophene, and MXenes (V2C(OH)2, V2CF2, Nb2C(OH)2, Nb2CF2, Nb2CO2, Hf2C(OH)2, Hf2CF2) were used as electrodes for FET fabrication. The interfacial electronic properties of electrodes and PtSe2 were studied in both the vertical and lateral directions using the ab initio method. In the vertical direction, PtSe2 formed ohmic contacts with most of the 2D metals except for Nb2CF2 and Hf2CF2. Specifically, in the cases of Nb2CF2 and Hf2CF2, p- and n-type Schottky contacts were formed with Schottky barrier heights (SBHs) of 0.48 eV and 0.02 eV, respectively. In the lateral direction, PtSe2 with contacting Hf2CF2 and V2C(OH)2 electrodes formed n-type Schottky contacts with SBHs of 0.14 eV and 0.09 eV, respectively. In the cases of TaS2 and Nb2CF2 electrodes, p-type Schottky contacts with SBHs of 0.35 eV and 0.29 eV, respectively, were formed. Moreover, n-type ohmic contacts were observed when Hf2C(OH)2 and Nb2C(OH)2 electrodes were applied, and p-type ohmic contacts were formed when borophene, NbSe2, Nb2CO2, and V2CF2 electrodes were used. This work reports a systematic investigation of ML PtSe2-2D metal interfaces and serves as a practical guide for selecting electrode materials for PtSe2 FETs.

Controllable construction of red thermally activated delayed fluorescence molecules based on a spiro-acridine donor.

Red and near-infrared (NIR) thermally activated delayed fluorescence (TADF) molecules show excellent potential applications in organic light-emitting diodes (OLEDs). Due to the lack of systematic studies on the relationship between molecular structures and luminescence properties, both the species and amounts of red and NIR TADF molecules are far from meeting the requirements for practical applications. Herein, four new efficient molecules (DQCN-2spAs, TPCN-2spAs, DPCN-2spAs and BPCN-2spAs) are proposed and their photophysical properties are theoretically predicted based on first-principles calculations and thermal vibration correlation function (TVCF) theory. The results show that all molecules exhibit red or NIR emissions and they have fast radiative decay rates and reverse intersystem crossing (RISC) rates, and the excellent TADF luminescence properties are predicted. Moreover, based on spiro-acridine (spAs) as the donor unit, the combination with different acceptors can change the dihedral angle between the ground state and the excited state, the bending degree of the donor is positively correlated with the reorganization energy, and this feature can have a great influence on the non-radiative process. Furthermore, based on these theoretical predictions, experimental verifications are performed and the synthesized BPCN-2spAs is confirmed to be an efficient NIR TADF molecule. Thus, the relationships between basic molecular structures and photophysical properties are revealed, a feasible design strategy is applied and four promising red and NIR TADF molecules are proposed. All these results could contribute to the development of red and NIR TADF emitters and OLEDs.

Role of halogen effects and cyclic imide groups in constructing red and near-infrared room temperature phosphorescence molecules: theoretical perspective and molecular design.

Organic room temperature phosphorescence (RTP) has been widely investigated to realize long-lifetime luminescent materials and improvement in their efficiency is a key focus of research, especially for red and near-infrared (NIR) RTP molecules. However, due to the lack of systematic studies on the relationship between basic molecular structures and luminescence properties, both the species and amounts of red and NIR RTP molecules remain far from meeting the requirements of practical applications. Herein, based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, the photophysical properties of seven red and NIR RTP molecules in tetrahydrofuran (THF) and in the solid phase were theoretically studied. The excited state dynamic processes were investigated by calculating the intersystem crossing and reverse intersystem crossing rates considering the surrounding environmental effects in THF and in the solid phase using a polarizable continuum model (PCM) and quantum mechanics and molecular mechanics (QM/MM) method, respectively. The basic geometric and electronic data were obtained, Huang-Rhys factors and reorganization energies were analyzed, and natural atomic orbital was used to calculate the orbital information of the excited states. Simultaneously, the electrostatic potential distribution on molecular surfaces was analyzed. Further, intermolecular interactions were visualized using the molecular planarity binding independent gradient model based on Hirshfeld partition (IGMH). The results showed that the unique molecular configuration has the potential to achieve red and NIR RTP emission. Not only did the substitutions of halogen and sulfur make the emission wavelength red-shifted, but also linking the two cyclic imide groups could further make the emission wavelength longer. Moreover, we found that the emission characteristics of molecules in THF had a similar trend as in the solid phase. Based on this point, two new RTP molecules with long emission wavelengths (645 nm and 816 nm) are theoretically proposed and their photophysical properties are fully analyzed. Our investigation provides a wise strategy to design efficient and long-emission RTP molecules with an unconventional luminescence group.

Multi-resonance thermally activated delayed fluorescence molecules with intramolecular-lock: theoretical design and performance prediction.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules with narrow full width at half maximum (FWHM) have attracted much attention recently. In this work, 36 borane/amine (B/N) type MR-TADF molecules were theoretically designed by using an intramolecular-lock strategy and systematically studied based on first-principles calculations. It was found that intramolecular-lock at different positions and in different manners could induce different luminescent properties. The calculated oscillator strengths for PXZ-L2 and PTZ-L2 locking systems are weaker than that for 2DPABN (without intramolecular-lock), while the Cz-L1 and TMCZ-L1 locking could result in stronger oscillator strength. Though the calculated FWHM of all the systems with intramolecular-lock is higher than that of 2DPABN, the Cz, TMCz and DMAC locking at L1 or L2 would induce relatively small FWHM which is comparable to that of 2DPABN. Our calculation results indicate that intramolecular-lock could enhance the SOC values and decrease the energy gap between the first singlet excited state and the first triplet excited state, which is quite favorable to reverse intersystem crossing. The Cz, TMCz and DMAC locking systems could realize comparable and higher efficiency than 2DPABN, thus higher quantum efficiency could be obtained. Our calculation results indicate that the intramolecular-lock strategy is an effective method to realize the design of highly efficient MR-TADF emitters.

Exploring the luminescence properties and sensing mechanism of a turn-on TADF probe for sulfite.

Fluorescent probes with a microsecond lifetime have attracted much attention in biological detection. The luminescence properties and responsive mechanisms of a probe [DCF-MPYM-lev-H]- for detecting sulfite and its corresponding product [DCF-MPYM-2H]2- are studied based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations as well as the thermal vibration correlation function method. It is found that the luminescence efficiency of the probe increases obviously after reacting with sulfite, which is induced by increased radiative decay rates and decreased nonradiative rates. In addition, the thermally activated delayed fluorescence (TADF) properties of products are confirmed by analyzing the spin-orbital constants and energy gaps between the singlet excited states and the triplet excited states. The calculation results favor the understanding of the luminescence properties and responsive mechanism of a turn-on TADF probe for sulfite, which may provide a theoretical reference for the development of new TADF probes.

Regulating the electronic properties of the WGe2N4 monolayer by adsorption of 4d transition metal atoms towards spintronic devices.

We study the regulation of the electronic and spin transport properties of the WGe2N4 monolayer by adsorbing 4d transition metal atoms (Y-Cd) using density functional theory combined with non-equilibrium Green's function. It is found that the adsorption of transition metal atoms (except Pd, Ag and Cd atoms) can introduce a magnetic moment into the WGe2N4 monolayer. Among the transition metal atoms, the adsorption of Nb and Rh atoms transforms WGe2N4 from a semiconductor to a half-metal and a highly spin-polarized semiconductor, respectively. The half-metallic Nb-adsorbed WGe2N4 system is selected to investigate the spin transport properties, and a high magnetoresistance ratio of 107% is achieved. In both parallel and antiparallel magnetization configurations, the spin filtering efficiency reaches close to 100% in the whole bias range, and the antiparallel magnetization configuration exhibits a dual spin filtering effect with a rectification ratio of up to 104. Our study predicts that the adsorption of 4d transition metal heteroatoms is an effective method to regulate the electronic and magnetic properties of WGe2N4 towards high-performance spintronic devices.

Efficient deep red/near-infrared thermally activated delayed fluorescence emitters via molecular reconstruction: theoretical insights.

Thermally activated delayed fluorescence (TADF) molecules with deep-red (DR) and near-infrared (NIR) luminescence show great potential in biomedical sensing/imaging and telecommunications. However, developing efficient DR- and NIR-TADF molecules remains a powerful challenge, and new design strategies are highly desired. Based on 2,3-bis(4-(diphenylamino)phenyl)quinoxaline-5,8-dicarbonitrile (CNQ-TPA), two novel TADF molecules CNQ-b-TPA and CNQ-f-TPA are theoretically constructed through the design strategy of molecular bonding and molecular fusion. The photophysical properties and luminescence mechanisms of the three molecules in toluene and the crystal state are revealed with first-principles calculations and the thermal vibration correlation function (TVCF) method. Compared with CNQ-TPA, CNQ-b-TPA and CNQ-f-TPA can achieve an effective red-shift of intrinsic emission and efficient DR and NIR emission. Remarkably, molecular bonding and molecular fusion not only greatly increase the oscillator strength, but also effectively reduce the energy gap between the first singlet excited state (S1) and the first triplet excited state (T1), resulting in their high radiative and reverse intersystem crossing rate. Moreover, the charge transport properties are studied based on kinetic Monte Carlo simulations. Molecular bonding to balance charge transport is found, enabling ambipolar transport properties. Our work provides a feasible solution to overcome the design limitations of previous DR- and NIR-TADF materials and predicts good candidates for both DR- and NIR-TADF emitters.

Design of multifunctional spin logic gates based on manganese porphyrin molecules connected to graphene electrodes.

The spin-resolved transport properties of molecular logic devices composed of two Mn porphyrin molecules connected to each other via a six-carbon atomic chain were studied using the non-equilibrium Green's function combined with density functional theory. The molecules were symmetrically connected to armchair graphene nanoribbon electrodes through four-carbon atomic chains on the left- and right-hand sides. Our calculations revealed that the spin-resolved current-voltage curves depend on the initial spin setting of the transition metal Mn atoms and carbon atoms on the zigzag edges where the electrodes come in contact with the molecule. By simultaneously regulating the spin orientations of the intermediate functional molecules and the zigzag edges of the armchair graphene nanoribbon electrodes, seven spin polarization configurations were obtained. These configurations were examined in this study considering the spin-related symmetry of molecular junctions. By meticulously selecting different combinations according to the specific input and output signals, YES, NOT, OR, NOR, and XOR multifarious spin logic devices were created. The findings of this study are expected to contribute toward the extension of molecular junction functions in future spintronic integrated circuit design and further miniaturization.

A theoretical perspective of the relationship between the structures and luminescence properties of red thermally activated delayed fluorescence molecules.

Orange and red thermally activated delayed fluorescence (TADF) emitters have shown promising applications in organic light emitting diodes (OLEDs) and the bio-medical field. However, both the species and amounts of orange and red molecules are far from meeting the requirement for practical applications; this is due to the lack of systematic studies on the relationship between molecular structures and luminescence properties. Herein, the excited state dynamic processes and photophysical properties of six donor-acceptor (D-A) type orange-red TADF molecules, which possess the same acceptor, are theoretically studied in toluene by using the polarizable continuum model (PCM). Based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the thermal vibration correlation function (TVCF) method, the adiabatic singlet-triplet energy gaps, natural transition orbital properties, reorganization energies, hole and electron distributions, and the radiative and non-radiative as well as the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes are theoretically analyzed. The results indicate that remarkable geometric changes between the lowest singlet excited state (S1) and the ground state (S0) are mainly caused by the rotation of the donor unit for NAI-R2, NAI-R3 and NAI-DPAC, and the reorganization energy is mainly contributed by the dihedral angle. However, for NAI-DMAC, BTDMAc-NAI and BFDMAc-NAI, remarkable geometric changes are found in the acceptor unit with large contribution of reorganization energy by bond length. These variations bring different non-radiative energy consumption processes. Moreover, small energy gaps between S1 and the lowest triplet excited state (T1) are determined for all studied molecules and an efficient RISC process is detected. Furthermore, enhanced conjugacy in the donor unit and remarkable intramolecular interactions are determined for BTDMAc-NAI and BFDMAc-NAI, which is helpful to promote the up-conversion process. Our investigations give reasonable explanations for previous experimental measurements and the relationship between basic structures and luminescence properties is revealed, which could facilitate the development of new efficient TADF emitters.

Schottky diodes based on blue phosphorene nanoribbon homojunctions.

Diodes have been widely studied as one of the most commonly used electronic components in circuits, and it is important to find diodes with an excellent rectification performance. Herein, we investigate the electronic and transport properties of Schottky contact diodes based on zigzag hydrogenated blue phosphorene nanoribbons, by employing density functional theory combined with the non-equilibrium Green's function. It is found that the adsorption of transition metal atoms Sc/Cr/Ti and Ni on the top site of blue phosphorene nanoribbons leads to metallic and semiconducting properties, respectively. Devices consisting of the planar contact of the metallic and semiconducting nanoribbons show rectifying behavior due to the Schottky barriers of the homojunctions. The current is preferential to flow from the semiconducting side to the metallic side. The rectification ratio of the Sc-Ni device and the Cr-Ni device can reach up to 108, which is much higher than that of traditional p-n junctions of about 105-107. The high rectification ratio at low bias regions, together with the low threshold voltages and negligible reverse currents, make blue phosphorene nanoribbon homojunctions ideal rectifier diodes.

The mechanism of intramolecular halogen bonding enhanced the quantum efficiency of ultralong organic phosphorescence in the aggregated state.

Ultralong organic phosphorescence (UOP) has broad application prospects in many fields, but realizing its high quantum efficiency is still full of challenges. One of the main reasons is that the internal luminescence mechanism is unclear and theoretical investigations to reveal the inner structure-property relationship are highly desired. Herein, the internal mechanism of halogen bonding enhancing the quantum efficiency of UOP is studied through the combination of quantum mechanics and molecular mechanics methods coupled with the thermal vibration correlation function (TVCF) method. Geometric and electronic data are obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Transition properties, energy gaps, intermolecular interactions, excited state dynamics as well as Huang-Rhys factors and reorganization energies are analyzed in detail. The results show that the high phosphorescence quantum efficiency benefits from the fast intersystem crossing (ISC) process and the slow non-radiative decay process. The halogen bonding, which cooperates with the effects of aromatic carbonyl and heavy atoms, not only accelerates the ISC rate by increasing the spin-orbit coupling effect, but also restricts the molecular motion and reduces the non-radiative energy consumption. Furthermore, through wise molecular design, an efficient UOP molecule with fast ISC and slow non-radiative decay rates is proposed. This work provides an insight into realizing efficient UOP emission via intramolecular halogen bonding.