Current spin polarization of a platform molecule with compression effect

Using the first-principles method, the spin-dependent transport properties of a novel platform molecule containing a freestanding molecular wire is investigated by simulating the spin-polarized scanning tunneling microscope experiment with Ni tip and Au substrate electrodes. Transport calculations show that the total current increases as the tip gradually approaches to the substrate, which is consistent with the conductance obtained from previous experiment. More interestingly, the spin polarization (SP) of current modulated by compression effect has the completely opposite trend to the total current. Transmission analyses reveal that the reduction of SP of current with compression process originates from the promotion of spin-down electron channel, which is controlled by deforming the molecule wire. In addition, the density of states shows that the SP of current is directly affected by the organic-ferromagnetic spinterface. The weak orbital hybridization between the Ni tip and propynyl of molecule results in high interfacial SP, whereas the breaking of the C $\equiv$ C triple of propynyl in favor of the Ni-C-C bond induces the strong orbital hybridization and restrains the interfacial SP. This work proposes a new way to control and design the SP of current through organic-ferromagnetic spinterface using functional molecular platform.     

Spin-excited states and rectification in an organic spin rectifier

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent trans- mission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.     

D-A型二噻吩并磷杂茂衍生物分子的双光子吸收性质

在密度泛函理论理论水平上,采用响应理论方法计算了一系列2,6-donor-acceptor 二噻吩并磷杂茂衍生物分子的单、双光子吸收性质. 理论计算结果表明该系列分子都具有较大的双光子吸收截面,并且分子中心的磷原子无论被氧化还是金属配合,其双光子吸收截面几乎保持不变. 此外,还考虑了溶剂效应对分子光学性质的影响,研究表明分子能级发生了溶剂化蓝移,并且分子的单光子和双光子吸收性质随着溶剂极性表现出非单调变化.     

The theoretical studies on the two-photon absorption properties of symmetric l,4-bis{2-[4-(2-aryl)phenyl]vinyl}-2,5-bisdialkoxybenzenes

<正>On the level of the time-dependent hybrid density functional theory,the one- and two-photon absorption properties of a series of symmetric 4-bis{2-[4-(2-aryl) phenyl]vinyl}-2,5-bisdialkoxybenzenes are studied respectively utilizing the analytic response theory and the few-state model methods.The calculated results show that the planarity of the geometrical structure plays a great role in enhancing the linear and nonlinear optical abilities of the molecule.However the effect of the length of the chain linked to theπ-centre on the optical property is very little.For the investigated compounds,the A-π-A type charge-transfer molecules display more superior one- and two-photon absorption characteristics than the D-π-D type ones.Furthermore,the two-photon absorption results by use of few-state model are generally consistent with those by analytic response theory,demonstrating the reliability of the few-state model for evaluating the two-photon absorption cross section.The numerical simulations are in good agreement in tendency with the available experimental measurements.     

Theoretical verification of intermolecular hydrogen bond induced thermally activated delayed fluorescence in SOBF-Ome

Thermally activated delayed fluorescence (TADF) molecules have attracted great attention as high efficient luminescent materials. Most of TADF molecules possess small energy gap between the first singlet excited state (S₁) and the first triplet excited state (T₁) to favor the up-conversion from T₁ to S₁. In this paper, a new TADF generation mechanism is revealed based on theoretical simulation. By systematic study of the light-emitting properties of SOBF-OMe in both toluene and in aggregation state, we find that the single SOBF-OMe could not realize TADF emission due to large energy gap as well as small up-conversion rates between S₁ and T₁. Through analysis of dimers, we find that dimers with intermolecular hydrogen bond (H-bond) are responsible for the generation of TADF, since smaller energy gap between S₁ and T₁ is found and the emission wavelength is in good agreement with experimental counterpart. The emission properties of SOBF-H are also studied for comparison, which reflect the important role of H-bond. Our theoretical results agree ith experimental results well and confirm the mechanism of H-bond induced TADF.     

(E,E)-1,4-双{2''-[5''-(B,B-二甲基苯硼)-2-噻吩基]乙烯基}-苯分子双光子吸收特性的理论研究

在密度泛函水平上,利用响应函数方法,研究了分子的单光子和双光子吸收特性.计算出了该分子在低能量范围内的最大双光子吸收截面为6.47×10-47 cm4 s/photon,与实验符合的较好.研究结果表明该分子具有较强的双光子吸收特性,是较好的双光子吸收材料.     

三嗪基热活化延迟荧光发射体的第一性原理研究

Three kinds of triazine based organic molecules designed for thermally activated delayed fluorescence (TADF) emitters are investigated by first-principles calculations. An optimal Hartree-Fork (HF) method is adopted for the calculation of energy gap between the first singlet state (S1) and the first triplet state (T1). The natural transition orbital, the electronhole (e-h) distribution and the e-h overlap diagram indicate that the S1 states for the three systems include both charge-transfer and some localized excitation component. Further quantitative analysis of the excitation property is performed by introducing the index Δr and the integral of e-h overlap S. It is found that symmetric geometry is a necessary condition for TADF emitters, which can provide more delocalized transition orbitals and consequently a small S1-T1 energy gap. Artful inserting aromatic groups between donors and acceptors can significantly enhance the oscillator strength. Finally, the energy state structures calculated with the optimal HF method is presented, which can provide basis for the study of the dynamics of excited states.     

级联三能级模型下超短脉冲激光与分子相互作用的动力学研究

通过求解麦克斯韦-布洛赫方程，研究了超短脉冲激光和一维对称π共轭分子材料(4,4′-二甲氨基二苯乙烯分子)的相互作用.该分子材料具有较强的非线性光学性质，其分子的电子结构和电偶极矩是在密度泛函理论水平上利用从头计算方法得到的.研究结果表明，慢变幅近似和旋波近似不能很好地描述超短脉冲在该分子介质中的传播.在单光子共振情况下，保持入射脉冲的脉冲宽度不变，当小面积脉冲在该分子介质中传播时，二能级模型可以较好地描述脉冲激光与该分子体系的相互作用过程.但对于大面积脉冲激光，由于较明显地产生了分子的二次激发，此时分子 关键词： 超短脉冲激光 4′-二甲氨基二苯乙烯分子 三能级模型 麦克斯韦-布洛赫方程     

超短脉冲激光在硝基苯胺分子材料中的非共振传播

通过严格求解麦克斯韦-布洛赫方程,研究了超短脉冲激光与硝基苯胺分子材料的非共振相互作用.研究结果表明,当脉冲激光在该分子介质中以电荷转移态的激发能的二分之一非共振传播时,脉冲激光频谱中明显地出现了二次谐波成分,显示了该分子具有较强的双光子吸收性质.     

Solvent effects on optical properties of a newly synthesized two-photon polymerization initiator： BPYPA

Time-dependent hybrid density functional theory in combination with polarized continuum model is applied to study the solvent effects on the geometrical and electronic structures as well as one- and two-photon absorption processes, of a newly synthesized asymmetrical charge-transfer organic molecule bis-（4-bromo-phenyl）-[4-（2-pyridin-4-yl-vinyl）phenyl]-amine （BPYPA）. There exist two charge-transfer states for the compound in visible region. The two-photon absorption cross section calculated by a three-state model and solvatochromic shift of the charge-transfer states are found to be solvent-dependent, where a nonmonotonic behaviour with respect to the polarity of the solvents is observed. The numerical results show that the organic molecule exhibits a rather large two-photon absorption cross section as compared with the compound 4-trans-[p-（N, N-Di-n-butylamino）-p-stilbenyl vinyl] pyridine （DBASVP） reported previously, and is predicted to be a good two-photon polymerization initiator. The hydrogen-bond effect is analysed. The computational results are in good agreement with the measurements.