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Recently, thermally activated delayed fluorescence (TADF) molecules with through-space charge transfer (TSCT) features have been widely applied in developing organic light-emitting diodes with high luminescence efficiencies. The performance of TSCT-TADF molecules depends highly on their molecular structures. Therefore, theoretical investigation plays a significant role in designing novel highly efficient TSCT-TADF molecules. Herein, we theoretically investigate two recently reported TSCT-TADF molecules, 1′-(2,12-di-t-butyl[1,4]benzoxaborinino[2,3,4-kl]phenoxaborinin-7-yl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (AC-BO) and 1-(2,12-di-t-butyl[1,4]benzoxaborinino[2,3,4-kl]phenoxaborinin-7-yl)-9′,9′-dimethyl-9′H-spiro [fluorene-9,5′-quinolino[3,2,1-de]acridine](QAC-BO). The calculated photophysical properties (e.g. excited state energy levels and luminescence properties) for these two compounds are in good agreement with experimental data. Based on the systematic analysis of structure–performance relationships, we design three novel TSCT-TADF molecules with high molecular rigidity and evident TSCT features, i.e., DQAC-DBO, DQAC-SBO, and DQAC-NBO. They exhibit deep-blue light emissions and fast reverse intersystem crossing rates (KRISCs). Our calculations demonstrate that the nearly coplanar orientation of the donor and acceptor is critical to achieve remarkable KRISCs and fluorescence efficiencies in TSCT-TADF molecules. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescent (TADF) materials that can exhibit both high emission efficiency and efficient reverse intersystem crossing (RISC) are highly desirable for achieving high-performance electroluminescence. However, attaining these two characteristics in TADF emitters is a challenging task that requires adherence to strict design principles. Here, we report two novel TADF emitters (CF3-Pym-DMAC and Ph-Pym-DMAC) featuring an asymmetric donor–acceptor–donor (D–A–D) molecular conformation, utilizing dimethylacridine donors and substituted-pyrimidine acceptors. The presence of different substituent groups, namely trifluoromethyl and phenyl, on pyrimidine acceptors can lead to significant variations in molecular conformations, packing modes, excited-state nature and luminescence properties. Specifically, the trifluoromethyl group forms strong intra-/intermolecular C–H⋯F hydrogen bonds, resulting in a fixed molecular conformation that enhances molecular rigidity and avoids intermolecular π–π stacking. Moreover, the substitution effect regulates the excited state alignments of these TADF molecules. As a result, compared to the phenyl-substituted molecule Ph-Pym-DMAC, the trifluoromethyl-substituted molecule CF3-Pym-DMAC exhibits a significantly higher PLQY (0.91 versus 0.36) and a much larger RISC rate (5.84 × 105 s−1versus 5.50 × 104 s−1). The substitution effect on these TADF emitters ultimately results in a more than threefold increase in maximum external quantum efficiency (EQEmax: 25.0% versus 6.7%) and a substantial reduction in efficiency roll-off for the TADF-OLEDs. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) molecular structures can achieve advantages, such as high fluorescence efficiency, reduced structural relaxation and narrow emission. It still remains a challenge to design highly efficient MR structure-based TADF materials with fast reverse intersystem crossing processes and easy emission-color tuning. Herein, we theoretically investigated the recently reported TADF molecule, which has the MR structure of quinolino[3,2,1-de] acridine-5,9-dione (QAD) as the acceptor and the moiety of carbazole (Cz) as the donor, namely QAD-Cz. The calculated fluorescence quantum efficiency of QAD-Cz is as high as 96.5%, which agrees with the experimental results (99.6%) very well. Moreover, we designed two new TADF materials based on the MR-QAD structure with different electron-donating moieties, namely QAD-TPA and QAD-DPTZ. The two newly designed molecules can theoretically achieve high fluorescence quantum efficiencies (over 90%) and fast reverse intersystem crossing rates (e.g. as high as 107 s−1 for QAD-DPTZ). The calculated emission wavelength of the QAD-DPTZ molecule is 638 nm, which obviously widens the emission color range of the reported MR-QAD-based TADF materials. Furthermore, we have analyzed the aggregation effects of the QAD-DPTZ molecule and demonstrated that this novel compound can likewise exhibit excellent luminescence performance in amorphous states. [ABSTRACT FROM AUTHOR]

Developing novel lead-free perovskite materials with suitable bandgaps and superior thermal stability is crucial to boost their applications in next-generation photovoltaic technologies. High throughput screening combined with the first principles method can accurately and effectively screen out promising perovskites. Herein, we select two lead-free all-inorganic halide double perovskite materials Cs2KMI6 (M = Ga, In) from 1026 compounds with the criteria including appropriate structure factors, positive decomposition energies, and suitable direct bandgaps. We investigated the thermal and mechanical stability, geometric and electronic structures, photoelectric properties, and defect formation energies for both perovskites Cs2KMI6 (M = Ga, In). They can exhibit excellent structural formability and stability through the analysis of structure factors, elastic constants, and stable chemical potential regions. In addition, we investigate the defect effects of Cs2KMI6 (M = Ga, In) on the photovoltaic performance by evaluating the defect formation energies and transition energy levels. Based on the HSE06 functional, we calculated the energy band structures of these two compounds and demonstrate the direct bandgaps of 1.69 eV (HSE06) and 2.16 eV (HSE06) for Cs2KGaI6 and Cs2KInI6, respectively. Moreover, we predicted excellent spectroscopic limited maximum efficiencies (SLMEs) of these two perovskites with high light absorption coefficients (around 105 cm−1), for instance, the SLME of Cs2KGaI6 can reach as high as 28.39%. [ABSTRACT FROM AUTHOR]

Recently, a family of [Fe2Co2] molecular capsules that display tunable electron transfer-coupled spin transition (ETCST) behavior were reported via a smart approach through Schiff-base condensation of aldehyde-functionalized 2,2-bipyridines (bpyCHO) and 1,7-heptanediamine (H2N(CH2)7NH2). Here, three more capsule complexes {[(TpR)Fe(CN)3]2[Co(bpyC＝N(CH2)nN＝Cbpy)]2[ClO4]2}·n(solvent) (1, TpR = Tp*, n = 5, sol = 8DMF; 2, TpR = TpMe, n = 9, sol = 5MeCN; and 3, TpR = Tp*, n = 11, sol = 5MeCN), where Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate and TpMe = hydridotris(3-methylpyrazol-1-yl)borate are reported, demonstrating a successful extension of such an approach with other alkyldiamines of different lengths. Combined X-ray crystallographic, infrared spectroscopic and magnetic studies reveal incomplete electron transfer with either changing temperature or upon light exposure. [ABSTRACT FROM AUTHOR]

The certified power conversion efficiency of perovskite solar cells is gradually approaching that of crystalline silicon solar cells. Accordingly, considering the advantages of improved thermal stability and environmental friendliness of lead-free all-inorganic halide double perovskites (LFAIHDPs), they have attracted considerable attention in optoelectronic applications. Herein, we review the recent progress on LFAIHDPs via heterovalent substitution of the lead element, including their geometrical and electronic structures, synthetic processes, and applications in optoelectronic devices. Many experimental and theoretical efforts have been devoted to investigating the thermal stability, defects, and optoelectronic properties of lead-free all-inorganic halide double perovskite materials, which have been presented. Lastly, we discuss the application of machine learning strategies to predict novel perovskite structures with excellent thermal stability and optoelectronic performance. [ABSTRACT FROM AUTHOR]

It has been recognized that both the ligand fields and intermolecular interactions may greatly impact the electron-transfer-coupled spin transition (ETCST) events in switchable magnetic materials; however, the engineering of these factors within a given system is still challenging. In this article, we chose the 4,4′-substituent 2,2′-bipyridine derivatives as chelating ligands according to their increasing electron-donating strength and incremental potential for forming hydrogen bonds (bpyCHO,CH3(L1) < bpyCH2OH,CH3 (L2) < bpyCH2OH,CH2OH (L3)), and prepared three new [Fe2Co2] complexes, {[(Tp*)Fe(CN)3Co(L)2]2[ClO4]2}·Sol (1, L = L1, Sol = 4MeCN·2H2O; 2, L = L2, Sol = 3MeCN; 3, L = L3, Sol = 4MeOH; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate). X-ray crystallography studies revealed that all the complexes share similar cyanide-bridged [Fe2Co2] square compositions except for the different substituted groups of L ligands, which led to the clearly evidenced intercluster hydrogen bonds between the neighbouring hydroxyl groups in 2 and 3. As a result, 1 remained in the paramagnetic [Fe III,LS2 Co II,HS2 ] state over the whole temperature range, while 2 and 3 showed complete ETCST behaviour with the transition temperatures (T1/2) being 221 and 294 K, respectively. [ABSTRACT FROM AUTHOR]

Organic donor–acceptor (D–A) type thermally activated delayed fluorescence (TADF) materials exhibit high luminous quantum efficiencies and therefore attract considerable research interest as organic light-emitting diodes (OLEDs). Accurately calculating the photoluminescence efficiency is crucial for the design of new TADF materials. In this work, we comprehensively quantify the luminous quantum efficiencies and related photophysical process rates of dimethylacridan-based blue-color TADF emitters (AC-OSO and ACRXTN), and demonstrate that the higher reverse intersystem crossing rates (e.g. KRISC = 4.98 × 108 s−1) from T1 to S1 and the suppressed non-radiative decay rates (e.g. K Snr = 1.68 × 106 s−1) together lead to a theoretical luminous quantum efficiency of around 100%. Our calculations predict well fluorescence efficiencies observed in experiments (Φcal = 95%). In both molecules, the nonradiative rates of S1–S0 and reverse intersystem crossing rates are affected by the reorganization energies due to the twisting vibration of the donor DMAC and acceptor moiety. Our theoretical study on the TADF mechanism will be beneficial for designing highly efficient TADF based OLED materials. [ABSTRACT FROM AUTHOR]

Developing high-performance dopant-free hole transport materials (DF-HTMs) is critical to realizing stable perovskite solar cells (PSCs). Herein, a class of siloxane-terminated polymers (PBZ-Si) with low surface energy were studied as DF-HTMs in PSCs. These polymers have good film-forming properties with unique face-on orientation and suitable valence bands. More importantly, the siloxane-terminated side-chains exhibited fantastic multifunctionality, providing the polymer with sufficient solubility, increased hole mobility, passivation capability, and hydrophobicity. Furthermore, for the first time, we observed directly the preferential face-on molecular orientation of polymeric HTMs on perovskite films by grazing incidence wide-angle X-ray scattering. Finally, planar n–i–p PSCs employing PBZ-3Si with complete siloxane-terminated side chains as the DF-HTM displayed a high efficiency of 20.18%, with an unprecedented fill factor up to 85%, a record fill factor value in all n–i–p PSCs with dopant-free HTMs. Moreover, the device with PBZ-3Si showed excellent thermal and moisture stability. The devices without encapsulation retained 76% of the initial efficiency after 333 h under 85 °C and 70 ± 10% relative humidity conditions. This work proves that siloxane-terminated side-chains are essential for the rational design of polymeric DF-HTMs toward efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Organic molecules with thermally activated delayed fluorescence (TADF) and aggregation induced emission (AIE) properties have attracted increasing research interest due to their great potential applications in organic light emitting diodes (OLEDs), especially for those with multicolor mechanochromic luminescence (MCL) features. Theoretical research on the luminescence characteristics of organic TADF emitters based on the aggregation states is highly desired to quantify the relationship between the TADF properties and aggregation states. In this work, we study the 4,4′-(6-(9,9-dimethylacridine-10(9H)-yl)quinoline-2,3-dibenzonitrile (DMAC-CNQ) emitter with TADF and AIE properties, and calculate the photophysical properties in gas, solid and amorphous states by using the quantum mechanics and molecular mechanics (QM/MM) method. Our simulations demonstrate that the aggregation states enhance obviously the reverse intersystem crossing rates and transition dipole moments of the DMAC-CNQ emitter, and suppress the non-radiative rates from the lowest excited singlet state (S1) to ground state (S0). Specifically, the molecular stacking of DMAC-CNQ in solid phases can mainly restrict the geometric torsion of the DMAC moiety for decreasing non-radiative decay rates, and the torsion of the CNQ moiety for increasing the reverse intersystem crossing rates. As a result, the calculated fluorescence efficiencies of the DMAC-CNQ emitter in the crystal and amorphous states are 67% and 26% respectively, and in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A supramolecular polymer has been prepared by sequential assembly of a distyrylanthracene derivative monomer with CB[7] and CB[8], which exhibits enhanced near infrared emission in the solid state on account of aggregation induced emission and noncovalent isolation effects. The supramolecular polymer forms spherulite layers followed by surface nucleation and 2D growth, and eventually constructs pyramidal crystalline aggregates with a size of about 500 nm. The preliminary study presents the supramolecular polymers crystallization behavior which relates to the aggregation states and functionalities of polymeric supramolecular materials and is worth further investigation both in theory and experiments. [ABSTRACT FROM AUTHOR]

In the present work, we have introduced a series of stable radical-doped coordination compounds composed of donor–acceptor structures and shown to produce organic radicals in situ as a result of unconventional lone pair–π interactions in ambient conditions. Inconspicuous lone pair–π and C–H⋯π interactions were shown to play a key role in self-assembly as well as the charge transfer process, resulting in a long-lived charge-separated state able to generate organic radicals. The resultant species displayed broad-spectrum antimicrobial activity, including against multi-drug-resistant bacteria. This study unveiled the promise of reactive organic radical-doped materials as a new platform for developing antimicrobial agents that can overcome antibiotic resistance. [ABSTRACT FROM AUTHOR]

Li/CFx cells possess the highest energy density among all lithium primary batteries. Here, the electrochemical lithiation process is elucidated through high-resolution 19F NMR, in situ7Li NMR and TEM methods. Fluorinated carbon CFL (L is around 0.06 or less) is identified for the first time to be generated in the discharge process of CFx (x ≥ 0.5) besides LiF and carbon. Moreover, the morphological evolution of the formed LiF, which affects the impedance of the battery during discharge, is illustrated as crystal nuclei of LiF, with a size of around 10 nm, which keep forming and growing into crystal grains of LiF, with a size of around 200 nm, until the surface of the CFx particles is saturated by LiF and then both crystal nuclei and grains enlarged promptly towards the end of lithiation. This work reveals the electrochemical reaction mechanism of CFx and provides crucial guidance to enhance the performance of the materials. [ABSTRACT FROM AUTHOR]

A sextuple ordered interpenetrated copper-naphthalenediimide network has been constructed by combining the features of porous metal–organic frameworks and π-conjugated supramolecular aggregation. The material exhibits intrinsic semiconductive features with narrow bandgap energy (1.2 eV) and outstanding electron transport. Theoretical calculations combined with experiments indicate that the high electron conduction may originate from π–d coupling and J-aggregation. [ABSTRACT FROM AUTHOR]

Lone pair-π interaction-induced charge-transfer was successfully used for switching the conductance of a coordination network, through variation of the degree of charge transfer caused by external photostimulation. The underlying mechanism is attributed to the changes in efficient charge-carriers by photoinduced strong charge transfer, which was investigated by in situ UV-Vis absorption, ESR, and computational studies. [ABSTRACT FROM AUTHOR]

Multiscale modeling has become a popular tool for research applying to different areas including materials science, microelectronics, biology, chemistry, etc. In this tutorial review, we describe a newly developed multiscale computational method, incorporating quantum mechanics into electronic device modeling with the electromagnetic environment included through classical electrodynamics. In the quantum mechanics/electromagnetics (QM/EM) method, the regions of the system where active electron scattering processes take place are treated quantum mechanically, while the surroundings are described by Maxwell's equations and a semiclassical drift-diffusion model. The QM model and the EM model are solved, respectively, in different regions of the system in a self-consistent manner. Potential distributions and current densities at the interface between QM and EM regions are employed as the boundary conditions for the quantum mechanical and electromagnetic simulations, respectively. The method is illustrated in the simulation of several realistic systems. In the case of junctionless field-effect transistors, transfer characteristics are obtained and a good agreement between experiments and simulations is achieved. Optical properties of a tandem photovoltaic cell are studied and the simulations demonstrate that multiple QM regions are coupled through the classical EM model. Finally, the study of a carbon nanotube-based molecular device shows the accuracy and efficiency of the QM/EM method. [ABSTRACT FROM AUTHOR]

The continuous downsizing of modern electronic devices implies the increasing importance of quantum phenomena. As the feature sizes of transistors inch towards 10 nanometer, simulations including quantum effects and atomistic details are inevitable. Here we report a novel hybrid quantum mechanics and electromagnetics (QM/EM) method to model individual electronic components at the nanoscale. QM and EM models are solved in different regions of the system in a self-consistent manner. As a demostration, we study a carbon nanotube based electronic device embedded in a silicon block. Good agreement is obtained between simulation by QM/EM method and full QM treatment of the entire system. [ABSTRACT FROM AUTHOR]

Developing novel lead-free perovskite materials with suitable bandgaps and superior thermal stability is crucial to boost their applications in next-generation photovoltaic technologies. High throughput screening combined with the first principles method can accurately and effectively screen out promising perovskites. Herein, we select two lead-free all-inorganic halide double perovskite materials Cs 2 KMI 6 (M = Ga, In) from 1026 compounds with the criteria including appropriate structure factors, positive decomposition energies, and suitable direct bandgaps. We investigated the thermal and mechanical stability, geometric and electronic structures, photoelectric properties, and defect formation energies for both perovskites Cs 2 KMI 6 (M = Ga, In). They can exhibit excellent structural formability and stability through the analysis of structure factors, elastic constants, and stable chemical potential regions. In addition, we investigate the defect effects of Cs 2 KMI 6 (M = Ga, In) on the photovoltaic performance by evaluating the defect formation energies and transition energy levels. Based on the HSE06 functional, we calculated the energy band structures of these two compounds and demonstrate the direct bandgaps of 1.69 eV (HSE06) and 2.16 eV (HSE06) for Cs 2 KGaI 6 and Cs 2 KInI 6 , respectively. Moreover, we predicted excellent spectroscopic limited maximum efficiencies (SLMEs) of these two perovskites with high light absorption coefficients (around 10 5 cm -1 ), for instance, the SLME of Cs 2 KGaI 6 can reach as high as 28.39%.

Recently, a family of [Fe 2 Co 2 ] molecular capsules that display tunable electron transfer-coupled spin transition (ETCST) behavior were reported via a smart approach through Schiff-base condensation of aldehyde-functionalized 2,2-bipyridines (bpy CHO ) and 1,7-heptanediamine (H 2 N(CH 2 ) 7 NH 2 ). Here, three more capsule complexes {[(Tp R )Fe(CN) 3 ] 2 [Co(bpy CN(CH 2 ) n NC bpy)] 2 [ClO 4 ] 2 }· n (solvent) (1, Tp R = Tp*, n = 5, sol = 8DMF; 2, Tp R = Tp Me , n = 9, sol = 5MeCN; and 3, Tp R = Tp*, n = 11, sol = 5MeCN), where Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate and Tp Me = hydridotris(3-methylpyrazol-1-yl)borate are reported, demonstrating a successful extension of such an approach with other alkyldiamines of different lengths. Combined X-ray crystallographic, infrared spectroscopic and magnetic studies reveal incomplete electron transfer with either changing temperature or upon light exposure.

It has been recognized that both the ligand fields and intermolecular interactions may greatly impact the electron-transfer-coupled spin transition (ETCST) events in switchable magnetic materials; however, the engineering of these factors within a given system is still challenging. In this article, we chose the 4,4'-substituent 2,2'-bipyridine derivatives as chelating ligands according to their increasing electron-donating strength and incremental potential for forming hydrogen bonds (bpy CHO,CH 3 (L1) < bpy CH 2 OH,CH 3 (L2) < bpy CH 2 OH,CH 2 OH (L3)), and prepared three new [Fe 2 Co 2 ] complexes, {[(Tp*)Fe(CN) 3 Co(L) 2 ] 2 [ClO 4 ] 2 }·Sol (1, L = L1, Sol = 4MeCN·2H 2 O; 2, L = L2, Sol = 3MeCN; 3, L = L3, Sol = 4MeOH; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate). X-ray crystallography studies revealed that all the complexes share similar cyanide-bridged [Fe 2 Co 2 ] square compositions except for the different substituted groups of L ligands, which led to the clearly evidenced intercluster hydrogen bonds between the neighbouring hydroxyl groups in 2 and 3. As a result, 1 remained in the paramagnetic [FeIII,LS2CoII,HS2] state over the whole temperature range, while 2 and 3 showed complete ETCST behaviour with the transition temperatures ( T 1/2 ) being 221 and 294 K, respectively.