Superior End-Group Stacking Promotes Simultaneous Multiple Charge-Transfer Mechanisms in Organic Solar Cells with an All-Fused-Ring Nonfullerene Acceptor.

The all-fused-ring acceptor (AFRA) is a success for nonfullerene materials and has attracted considerable attention as its high optical and chemical stability expected to reduce energy loss, and power conversion efficiency (PCE) approaching 15% in constructed all-small-molecule organic solar cells (OSCs). Herein, the intrinsic role of the structure of AFRA F13 and the reason for its high PCE were revealed by comparison with those of typical fused acceptors IDT-IC and Y6. An increased degree of conjugation in F13 leads to broader and red-shifted absorption peaks, facilitating enhancement of the short-circuit current. Multiple charge-transfer mechanisms are mainly attributed to the higher Frenkel exciton (FE) state due to the multiple transition ways for acceptors in the C1-CN:F13 system. The increased number of atoms contributing to the charge-transfer (CT) state facilitated the existence of more superior stacking patterns with easy formation of CT and FE/CT states and a high charge separation rate. It was found using the AFRA is an effective strategy to enhance end-group stacking, enhancing the borrowing of oscillator strength to promote multiple CT mechanisms in the complexes, explaining the high performance of this OSC device. This work is promising to guide designing an efficient AFRA in the future.

A Theoretical Study on the Underlying Factors of the Difference in Performance of Organic Solar Cells Based on ITIC and Its Isomers.

Recently, non-fullerene-based organic solar cells (OSCs) have made great breakthroughs, and small structural differences can have dramatic impacts on the power conversion efficiency (PCE). We take ITIC and its isomers as examples to study their effects on the performance of OSCs. ITIC and NFBDT only differed in the side chain position, and they were used as models with the same donor molecule, PBDB-T, to investigate the main reasons for the difference in their performance in terms of theoretical methods. In this work, a detailed comparative analysis of the electronic structure, absorption spectra, open circuit voltage and interfacial parameters of the ITIC and NFBDT systems was performed mainly by combining the density functional theory/time-dependent density functional theory and molecular dynamics simulations. The results showed that the lowest excited state of the ITIC molecule possessed a larger ∆q and more hybrid FE/CT states, and PBDB-T/ITIC had more charge separation paths as well as a larger kCS and smaller kCR. The reason for the performance difference between PBDB-T/ITIC and PBDB-T/NFBDT was elucidated, suggesting that ITIC is a superior acceptor based on a slight modulation of the side chain and providing a guiding direction for the design of superior-performing small molecule acceptor materials.

Mechanism of symbiotic nodulation between nitrogen and peanut.

Nitrogen is critical for peanut growth and development, and symbiotic nodulation and nitrogen fixation is one of the main ways for peanut to obtain nitrogen. The influence of exogenous nitrogen on nodule nitrogen fixation involves complex regulatory mechanisms, revealing the regulatory mechanisms of nitrogen on nodule nitrogen fixation is of great significance for realizing the potential of biological nitrogen fixation. In this review, we summarize the mechanism of "Crack entry" in the formation of peanut root nodule, the mechanism of symbiotic nodulation and quantitative regulation of peanut, and the regulatory mechanism of nitrogen affecting peanut nodulation. At present, the molecular mechanism by which nitrogen affects the interaction between Bradyrhizobium and peanut, thereby regulating nodulation, is still unclear. Therefore, future research should focus on the signal exchange, nodule number regulation, and nutrient exchange mechanism of nitrogen effects on Bradyrhizobium and peanut, which would provide a theoretical basis for improving nodule nitrogen fixation efficiency and peanut yield, and reduce chemical nitrogen fertilizer application.

The combination of skeleton-engineering and periphery-engineering: a design strategy for organic doublet emitters.

The emergence and development of radical luminescent materials is a huge breakthrough toward high-performance organic light-emitting diodes (OLEDs) without spin-statistical limits. Herein, we design a series of radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) by combining skeleton-engineering and periphery-engineering strategies, and present some insights into how different chemical modifications can modulate the chemical stability and luminescence properties of radicals by quantum chemistry methods. Firstly, through the analysis of the geometric structure changes from the lowest doublet excited state (D1) to the doublet ground state (D0) states, the emission energy differences between the BN orientation isomers are explained, and it is revealed that the radical with a smaller dihedral angle difference can more effectively suppress the geometric relaxation of the excited states and bring a higher emission energy. Meanwhile, a comparison of the excited state properties in different radicals can help us to disclose the luminescence behavior, that is, the enhanced luminescent intensity of the radical is caused by the intensity borrowing between the charge transfer (CT) state and the dark locally excited (LE) state. In addition, an efficient algorithm for calculating the internal conversion rate (kIC) is introduced and implemented, and the differences in kIC values between designed radicals are explained. More specifically, the delocalization of hole and electron wave functions can reduce nonadiabatic coupling matrix elements (NACMEs), thus hindering the non-radiative decay process. Finally, the double-regulation of chemical stability and luminescence properties was realized through the synergistic effect of skeleton-engineering and periphery-engineering, and to screen the excellent doublet emitter (BN-41-MPTTM) theoretically.

Theoretical Simulations of Thermochromic and Aggregation-Induced Emission Behaviors of a Series of Red-Light Anthracene-o-carborane Derivatives.

Quantum mechanical and molecular dynamics simulations have been carried out on a series of anthracene-o-carborane derivatives (ANT-H, ANT-Ph, ANT-Me and ANT-TMS) with rare red-light emission in the solid state. The simulation of the heating process of the crystals and further comparison of the molecular structures and excited-state properties before and after heating help us to disclose the thermochromic behavior, that is, the red-shift emission is caused by elongation of the C1-C2 bond in the carborane moiety after heating. Thus, we believe that the molecular structure in the crystal is severely affected by heating. Transformation of the molecular conformation appears in the ANT-H crystal with increasing temperature. More specifically, the anthracene moiety moves from nearly parallel to the C1-C2 bond to nearly perpendicular, causing the short-wavelength emission to disappear after heating. As for the aggregation-induced emission phenomenon, the structures and photophysical properties were investigated comparatively in both the isolated and crystal states; the results suggested that the energy dissipation in crystal surroundings was greatly reduced through hindering structure relaxation from the excited to the ground state. We expect that discussion of the thermochromic behavior will provide a new analysis perspective for the molecular design of o-carborane derivatives.

Insight into the optoelectronic characteristics of diimide-based acceptors in organic solar cells by performing DFT calculation and molecular dynamics simulation.

In order to compare the main difference of two diimide derivatives on the modulation of electronic and optical properties of P3HT-based organic solar cell, the density functional theory and molecular dynamics simulations were implemented to achieve elementary data on geometrical structure, molecular orbital, open-circuit voltage, absorption spectra, energetic driving force, and interface parameter of P3HT/D1 and P3HT/D2 systems. According to the investigation, P3HT/D1 system not only exhibits higher open circuit voltage and enough energetic driving force than P3HT/D2 system, but also possesses low-lying LUMO +1 orbital which can favor the exciton separation efficiency. Moreover, on the basis of some typical interface models choose from MD simulation, the estimation of the interface rate manifests that the P3HT/D1 interface possesses the smaller charge recombination rates and larger charge separation rates than those of the P3HT/D2 interface. It is expect that this work can provide certain guidelines for the further develop the performance of organic solar cell. We hope this work can further study on non-fullerene acceptor materials as a certain guides.

Exploring what prompts ITIC to become a superior acceptor in organic solar cell by combining molecular dynamics simulation with quantum chemistry calculation.

The interface characteristic is a crucial factor determining the power conversion efficiency of organic solar cells (OSCs). In this work, our aim is to conduct a comparative study on the interface characteristics between the very famous non-fullerene acceptor, ITIC, and a fullerene acceptor, PC71BM by combining molecular dynamics simulations with density functional theory. Based on some typical interface models of the acceptor ITIC or PC71BM and the donor PBDB-T selected from MD simulation, besides the evaluation of charge separation/recombination rates, the relative positions of Frenkel exciton (FE) states and the charge transfer states along with their oscillator strengths are also employed to estimate the charge separation abilities. The results show that, when compared with those for the PBDB-T/PC71BM interface, the CT states are more easily formed for the PBDB-T/ITIC interface by either the electron transfer from the FE state or direct excitation, indicating the better charge separation ability of the former. Moreover, the estimation of the charge separation efficiency manifests that although these two types of interfaces have similar charge recombination rates, the PBDB-T/ITIC interface possesses the larger charge separation rates than those of the PBDB-T/PC71BM interface. Therefore, the better match between PBDB-T and ITIC together with a larger charge separation efficiency at the interface are considered to be the reasons for the prominent performance of ITIC in OSCs.

A theoretical exploration of the effect of fluorine and cyano substitutions in diketopyrrolopyrrole-based polymer donor for organic solar cells.

A series of polymer donor materials 1-5 based on diketopyrrolopyrrole and thiophene unit which have been widely used in organic solar cells (OSCs) were investigated based on quantum chemical calculations. The effect of fluorine and cyano substitutions in polymer donor materials was focused on. Based on the investigation on electronic structures and optical properties of the reported molecules 1 and 2 and the analysis on some parameters relevant to charge dissociation ability at donor/acceptor interface constituted by 1 and 2 with PC61BM such as intermolecular charge transfer and recombination, driving force and Coulombic bound energy, we explained why fluorine substitution can improve OPV efficiency through strengthening eletron-withdrawing ability from a theoretical perspective. Then we designed cyano-substituted polymers 3-5 with the aim of obtaining better photovoltaic donor materials. The results reveal that our attempt to design donor materials which can balance large open-circuit voltage (Voc) and high short-circuit current (Jsc) in OSCs has worked out. It is worth noting that the substitutions of fluorine and cyano groups synergistically reduce energy gap and HOMO energy level of polymers 3 and 4. Moreover, 3/PC61BM and 4/PC61BM heterojunctions show over 107 and 104 times higher than 1/PC61BM on the ratios of intermolecular charge transfer and recombination rates (kinter-CT/kinter-CR). Thus, our work here may provide an efficient strategy to design promising donor materials in OPVs and we hope it could be useful in the future experimental synthesis.

Linear headache: clinical characteristics of eight new cases.

BACKGROUND: Linear headache (LH) has recently been described as a paroxysmal or continuous fixed head pain restricted in a linear trajectory of 5-10 mm in width, linking one endpoint in occipital or occipitocervical region with another endpoint in ipsilateral nasion or forehead region. For some patients, this headache had some features resembling migraine without aura. METHODS: We made a prospective search of patients presenting with a clinical picture comprised under the heading of LH and we have accessed eight new cases. A detailed clinical feature of the headache was obtained in all cases to differentiate with cranial neuralgia, paroxysmal hemicrania, cervicogenic headache, nummular headache and migraine. RESULTS: The eight LH patients complained of a recurrent moderate to severe, distending, pulsating, or pressure-like pain within a strictly unilateral line-shaped area. The headache duration would be ranged from 1 h to 2 days or persistent for 1-6 months with recurrent worsening of headaches. For some patients, this headache had couple of features similar to that of migraine pattern, such as accompaniments of nausea, vomiting, and phonophobia, diziness, triggering factors of noise, bright night, resting after physical activity, fatigue, menstruation, and response to anti-migraine therapy. CONCLUSIONS: This description reinforces the proposal of LH as a new headache syndrome or a new variant of a previously known headache syndrome, probably of migraine.

A recurrent headache circumscribed in a coronal line-shaped area around the head: a coronal linear headache.

BACKGROUND: Linear headache (LH) has recently been described as a paroxysmal or continuous head pain restricted in a linear trajectory of 5-10 mm in width, linking one endpoint in occipital or occipitocervical region with another endpoint in ipsilateral nasion or forehead region. The sagittal line-shaped pain area of LH is close and parallel to a sagittal venous sinus, the superior sagittal sinus (SSS). For some patients, the LH had some features resembling the pattern of migraine without aura. CASE DESCRIPTION: A 45 year-old woman complained with a distinct headache for more than half years. The pain trajectory of the headache is confined to a coronal line-shaped area of 5-10 mm in width linking the two points in the bilateral temporal regions with the occipital protuberance. This coronal line-shaped pain area is close and parallel to a coronal cambered venous sinus complex, the combination of the confluences of sinus and the bilateral cavernous sinus (CS), superior petrosal sinus (SPS) linking the CS with transverse sinus (TS) and TS into which the SPS feeds. The patient had a past history of migraine without aura for 10 years and her son had a benign paroxysmal vertigo (BPV) for 12 years. Both of her coronal line-shaped headache and her son's vertigo had well response to sodium valproate. DISCUSSION AND EVALUATION: Its clinical characteristics were distinctly different from those of other two headache entities defined with topographical criteria, nummular headache and epicrania fugax, and different from other existing headache entities except for migraine without aura. CONCLUSION: The distinct coronal line-shaped headache is suggestive of a variant of LH, a coronal LH, and probably belongs to a subtype of migraine without aura as proposed for LH. This coronal LH reinforces the proposal of LH as a new headache syndrome or a subtype of a previously known headache syndrome, probably of migraine.

Linear interictal pain in epicrania fugax: a reply.

This is a reply to the comments on our article "Linear headache: a recurrent unilateral head pain circumscribed in a line-shaped area" published in JHP 2014 Jun 26; 15:45. In the comments, the authors raise a question whether the linear headache (LH) we reported be a linear interictal pain in epicranial fugax (EF), based on a case they reported. We think that the LH is not a linear interictal pain in EF based on our observations and considerations.

Linear headache: a recurrent unilateral head pain circumscribed in a line-shaped area.

BACKGROUND: A headache circumscribed in a line-shaped area but not confined to the territory of one particular nerve had ever been described in Epicrania Fugax (EF) of which the head pain is moving and ultrashort. In a 25-month period from Feb 2012 to Mar 2014, we encountered 12 patients with a paroxysmal motionless head pain restricted in a linear trajectory. The head pain trajectory was similar to that of EF, but its all other features obviously different from those of EF. We named this distinctive but undescribed type of headache linear headache (LH). METHODS: A detailed clinical feature of the headache was obtained in all cases to differentiate with EF, trigeminal autonomic cephalalgias (TACs) and cranial neuralgia. Similarities and differences in clinical features were compared between LH and migraine. RESULTS: The twelve LH patients (mean age 43.9 ± 12.2) complained of a recurrent, moderate to severe, distending (n = 9), pressure-like (n = 3) or pulsating (n = 3) pain within a strictly unilateral line-shaped area. The painful line is distributed from occipital or occipitocervical region to the ipsilateral eye (n = 5), forehead (n = 6) or parietal region (n = 1). The pain line has a trajecory similar to that of EF but no characteristics of moving. The headache duration would be ranged from five minutes to three days, but usually from half day to one day in most cases (n = 8). Six patients had the accompaniment of nausea with or without vomiting, and two patients had the accompaniment of ipsilateral dizziness. The attacks could be either spontaneous (n = 10) or triggered by noise, depression and resting after physical activity (n = 1), or by stress and staying up late (n = 1). The frequency of attacks was variable. The patients had well response to flunarizine, sodium valproate and amitriptyline but not to carbamazepine or oxcarbazepine. LH is different from EF, trigeminal autonomic cephalalgias (TACs) and cranial neuralgia, but it had couple of features similar to that of migraine. CONCLUSIONS: The clinical picture of LH might be a subtype of migraine, or represent a novel syndrome.

Ophthalmoplegia starting with a headache circumscribed in a line-shaped area: a subtype of ophthalmoplegic migraine?

Recurrent painful ophthalmoplegic neuropathy (RPON), formerly named ophthalmoplegic migraine (OM), is a rare condition characterized by the association of unilateral headaches and the ipsilateral oculomotor nerve palsy. The third cranial nerve is most commonly involved in the recurrent attacks. But it is still debated whether a migraine or an oculomotor neuropathy may be the primary cause of this disorder. Here, we report an elder patient who had a recurrent ophthalmoplegia starting with an unilateral headache circumscribed in an area shaped in a line linking the posterior-parietal region and the ipsilateral eye. And the headache had couple of features similar to that of migraine, such as past history of recurrent migraine attacks, accompaniments of nausea, vomiting, and phonophobia, response to flunarizine and sodium valproate. We may herein report a subtype of OM but not a RPON. This case report indicates that OM may exist as an entity and some OM may be wrongly grouped under the category of RPON in the current international headache classification.