Synthesis,characterization, photophysical and electrochemical properties of oxygen bridged twisted heptatomic biphenyl substituted perylene diimides

The perylene diimide derivatives (s-THBPDI and d-THBPDI) bearing oxygen bridged twisty heptatomic biphenyl in the bay positions of the perylene core through acetylene bond were designed and synthesized. The photophysical properties of the functionalized dyes were investigated in solution and solid state by UV-vis and photoluminescence (PL) spectra. Their UV-vis and PL spectrum both exhibited the different concentration-dependent behaviors due to the difference of chemical structure. Moreover, cyclic voltammetry results indicated that the introduction of oxygen bridged twisted heptatomic biphenyl could decrease the LUMO energy level of the perylene diimide effectively and made it promising material in photoelectric devices.     

Ab initio configuration interaction study on electronically excited 4-dimethylamino-4′-cyanostilbene

Ab initio configuration interaction calculations have been performed to examine the electronic structures of both trans-4-dimethylamino-4′-cyanostilbene (DCS) and four types of perpendicularly twisted DCSs, trans-DCS is predominantly excited into the S₁ state out of low-lying excited states. The S₁ state is an intramolecular charge-transfer (ICT) state in which the dipole moment is about twice as large as that in S₀. The excited DCS at the 4-dimethylanilino twisted conformation, which becomes S₁ in polar solvents, has a very much larger dipole moment than that in S₁ to trans-DCS. This means that the geometrical structure of the twisted ICT (TICT) is the 4-dimethylanilino twisted form, not the dimethylamino twisted one which is well know from the TICT structure of 4-dimethylaminobenzonitrile. Received: 16 December 1998 / Accepted: 19 March 1999 / Published online: 9 September 1999     

Polarisation rotator consisting of two layers of twisted nematic LC,which shows little dependence on the initial polarisation direction and the wavelength

Performances of typical HWP (half-wave plate) or the one layer of the twisted nematic LC as the polarisation rotator are affected by the wavelength of the incident light and the initial polarisation direction of the incident linear polarisation. A new configuration that two layers of the twisted LC were aligned with the angular difference of 90°, was considered. Theoretical analysis by Jones matrix was used to derive the change of the polarisation state at the proposed configuration and to investigate the dependence on the wavelength and the initial polarisation direction. Commercial LC simulator was used to quantitatively investigate the effectiveness of the proposed configuration. Theoretical analysis and the calculated results show that the performance of the proposed configuration was less dependent on wavelength as compared with the one layer of twisted nematic LC.     

Conformation of p-terphenyl under hydrostatic pressure

The conformation of p-terphenyl (C18H14) and deuterated p-terphenyl (C18D14) has been investigated, using high-pressure infrared spectroscopy at liquid-helium temperatures. First-principles calculations, together with the experimental results, were performed to determine the structure of p-terphenyl in the twisted conformation. At low temperatures and pressures, p-terphenyl belongs to the C2 point group of symmetry. In this configuration, the central ring is twisted with respect to the plane of the outer rings. The symmetry of the molecule is nearly C2h, consistent with previous x-ray diffraction measurements.     

Absorption and fluorescence of PRODAN in phospholipid bilayers: a combined quantum mechanics and classical molecular dynamics study

Absorption and fluorescence spectra of PRODAN (6-propionyl-2-dimethylaminonaphthalene) were studied by means of the time-dependent density functional theory and the algebraic diagrammatic construction method. The influence of environment, a phosphatidylcholine lipid bilayer and water, was taken into account employing a combination of quantum chemical calculations with empirical force-field molecular dynamics simulations. Additionally, experimental absorption and emission spectra of PRODAN were measured in cyclohexane, water, and lipid vesicles. Both planar and twisted configurations of the first excited state of PRODAN were taken into account. The twisted structure is stabilized in both water and a lipid bilayer, and should be considered as an emitting state in polar environments. Orientation of the excited dye in the lipid bilayer significantly depends on configuration. In the bilayer, the fluorescence spectrum can be regarded as a combination of emission from both planar and twisted structures.     

Molecular self-assembly inhibition leads to basket-shaped cyclophane formation with chiral dynamics

Planar perylene derivatives form macrocyclic dimers and concatenated dimer-dimer rings under the action of molecular self-assembly. If this underpinning principle is true, highly twisted perylene derivatives should be more frustrated toward formation of multimeric cyclic compounds such as macrocyclic dimers and concatenated dimer-dimers because of perturbation resulting from intermolecular pi-pi stacking. Indeed, 1,6,7,12- tetraphenoxy-substituted perylene is highly twisted and undergoes unimolecular cyclization rather than bimolecular or multimolecular cyclization. The resulting monocyclic monomer exhibits interesting conformation switching from one chiral structure (left-handedness) to another chiral structure (right-handedness) at room temperature. NMR studies of conformational dynamics reveal that such configuration change between the two enantiomers can be frozen at low temperature (-45 degrees C). An activation enthalpy barrier of 13.4 +/- 0.5 kcal.mol-1 for twisting the perylene plane in order to convert from one enantiomer to the other has been found.     

Synthesis and crystal structure of aqua(diaminobithiazole) (iminodiacetato)nickel(II) hydrate

Crystals of the title compound, [(C₆H₆N₄S₂)(C₄H₅NO₄)(H₂O)Ni]·H₂O, consist of the Ni(II) complex and lattice water. The Ni(II) complex adopts a distorted octahedral coordination geometry formed by an iminodiacetate anion (IDA), a diaminobithiazole (DABT) and a coordinated water molecule. A twisted configuration of DABT is the distinguishing feature in the complex, the dihedral angle between thiazole rings of DABT being 20.04(8)°. An aromatic stacking interaction occurs between thiazole rings from neighboring complex molecules, and is considered as the reason for the twisted configuration. The tridentate IDA dianion chelates to a Ni(II) atom in afacialconfiguration. A hydrogen bond network holds the complex molecules together to form a supramolecular structure.     

Dynamic Chirality Control of tropos DPCB‐digold Skeleton by Chiral Binaphthyldicarboxylate

The planar 3,4‐diphosphinidenecyclobutene (DPCB) can be remarkably twisted into a C₂‐type helical structure by dual coordination of a AuCl moiety. A prompt chirality control of the twisted DPCB skeleton ligated by the digold units affords the enantiopure structure by exchanging the chloride ligands for chiral [1,1′‐binaphthalene]‐2,2′‐dicarboxylate. The chirality of the diaurated 2,2′‐bis(diphenylphosphanyl)‐1,1′‐biphenyl (BIPHEP) system can be controlled prior to that of DPCB. Mixing of a DPCB‐bis(chlorogold) complex with the chiral silver salt dynamically leads to a single diastereomer, which was characterized by the ³¹P NMR spectrum and the CD couplet patterns in the visible (DPCB) area. The absolute configuration of the singly induced helical structure was assigned by the theoretical CD spectra determined by TD‐DFT calculations. Intramolecular alkoxycyclization of hexa‐4,5‐dien‐1‐ol catalyzed by the asymmetric DPCB‐digold structure were also attempted.     

具有荧光发射能力有机化合物的光物理和光化学问题研究

有机化合物的结构、构象和环境效应对发光化合物的荧光发射具有重要的影响.本文从化合物激发态的衰变过程出发,侧重于过程的光化学与光物理问题对发光行为和机制进行讨论.如:化合物分子结构的受阻和桥键化对发光的影响;光激发下的光诱导电子和电荷转移及其相互转化;化合物扭曲的分子内电荷转移(TICT);溶剂分子和发光化合物分子间不同的相互作用及对发光的影响;在发光过程中存在着最佳的发光构象等.对于这些问题的研究和掌握,将有利于设计和合成具有高荧光量子产率的发光化合物,更好地解释在研究中出现的种种现象和在实际工作中应用它们.文章还引用了大量发光化合物作为实例,对工作中所得的结果进行了详细讨论.     

Large size, high efficiency fiber-shaped dye-sensitized solar cells

A high-efficiency dye-sensitized solar cell prototype has been designed and fabricated, in which the working electrode and counter electrode are in direct contact and singly twisted. The cell is sealed in a capillary. In this solar cell configuration, the area ratio between the counter and working electrode is extremely low which allows the independent adjustment of electrolyte volume and the distance between counter electrode and photo-anode. Also it is more easily sealed compared to planar solar cell. The effects of TiO(2) film thickness, twisted pitch of counter electrode and length of device have been investigated. Our results indicate that this novel configuration has demonstrated excellent modularization function, three dimensional light harvesting capacities and the relative independence of incident light angles due to the symmetry structure. The power conversion efficiency of one cell of 9.5 cm in length can reach up to 5.41% at standard test condition (100 mW cm(-2)) and the power output may double under intense diffuse illumination. As far as we know, this is the longest and most efficient fiber-shaped dye-sensitized solar cell consisting of liquid electrolyte. The longer the fiber-shaped solar cell is, the more suitable it is for woven solar power textile if it is encapsulated in transparent flexible plastic capillary.     

Instability of two–dimensional structure of dichalcogenin and dipnictogenin octa–heterocyclic systems with 1,2–C6X2(X = O,S, Se,Te, N,P) unsaturated rings

Structural Chemistry - The planar configuration and twisted structures of the dichalcogenin (DCG) and dipnictogenin (DPG) octa–heterocyclic systems with 1,2–C6X2 ring in their main...     

X射线单晶衍射研究系列功能七元杂环桥联联苯构象

含有七元杂环桥联联苯的π-共轭聚合物是重要的宽禁带光电材料, 其发光性质决定于两苯环间扭曲角. 利用X射线单晶衍射仪确定了系列功能的七元杂环桥联联苯化合物的晶体结构, 比较了桥联原子, 6,6位取代基及分子间弱氢键对这类桥联联苯扭曲构象的影响. 桥联键是—CH2—O—CH2—和—CH2—S—CH2—的七元杂环桥联联苯两苯环间的扭曲角分别为39°和51°, 在6,6位上含有不同取代基的双氧桥联七元杂环桥联联苯的扭曲角存在5°的差异. 在双氧桥联的七元杂环桥联联苯的二聚物中, 桥联的氧原子与非桥联的苯亚基-苯亚基2,2’位置上的两个氢原子之间形成的氢键网络结构导致中心联苯呈现平面构象, 但氢键并没有改变桥联联苯的构象. 七元杂环桥联联苯的构象主要由桥联原子决定, 同时分子间相互作用亦能轻微调控这类桥联联苯的扭曲角.     

(2Z)-3-(5-Hydroxy-4-oxo-4H-chromen-3-yl)acrylonitrile

The title compound, C₁₂H₇NO₃, consists of a chromone moiety substituted in position 3 with an acrylonitrile group in a Z configuration. The two planar groups are twisted with respect to one another. The only significant hydrogen bond in the structure is an intra­molecular O—H·O bond. π–π contacts connecting aromatic groups and C—H·O inter­molecular weak inter­actions lead to a supramolecular layer arrangement.     

Anchoring effects on the electrically controlled optical band gap in twisted photonic liquid crystals

We study a one-dimensional twisted photonic liquid crystal (TPLC), consisting of various nematic liquid crystal cells adopting a twisted configuration intercalated by isotropic dielectric layers, submitted to a dc electric field (E^dc ) aligned along the periodicity axis. We write the corresponding Euler–Lagrange equations describing the nematic layer configuration. By assuming arbitrary anchoring quasi-planar boundary conditions, we calculate the equilibrium textures for the nematic, parametrized by the two types of strength of its interaction (polar and azimuthal) with the plane walls. We write the electromagnetic equations in a 4?×?4 matrix representation and using the transfer matrix formalism, we obtain the transmittance and reflectance coefficients for normal incidence as functions of the external electric field and anchoring strengths. We have observed a remarkable dependence of the electric field on the transmission and reflection spectra in opening and closing band gaps.     

Fast polarisation-insensitive optical shutter supported by backflow in dichroic dye-doped dual-frequency liquid crystal

This paper describes a novel implementation of a dual-frequency liquid crystal optical shutter of the guest–host type. The transmissive state of the filter is obtained by applying a low-frequency electric field that brings the dichroic dye in a homeotropic orientation. The light-absorbing state is realised by a twisted planar configuration for which the absorption is quasi-independent of the polarisation. Switching between the two states occurs in about 1 ms and the devices show no scattering for wavelengths inside or outside the absorption band of the dichroic dye. Simulations and experiments reveal how a twisted state is obtained through the backflow phenomenon.     

STN-gels in fast passive matrix displays

Liquid crystalline physical gels have been prepared in a super twisted nematic configuration. These gels show a remarkable increase in switching speed from the in field to out of field relaxation. We explore whether these gels might be used in fast passive matrix displays.     

STN-gels in fast passive matrix displays

Liquid crystalline physical gels have been prepared in a super twisted nematic configuration. These gels show a remarkable increase in switching speed from the in field to out of field relaxation. We explore whether these gels might be used in fast passive matrix displays.     

Orientational transition in the cholesteric layer induced by electrically controlled ionic modification of the surface anchoring

A reorientation of cholesteric liquid crystal with a large helix pitch induced by the electrically controlled ionic modification of the surface anchoring has been studied. In initial state, the cholesteric helix is untwisted completely owing to the normal surface anchoring specified by the cations adsorbed at the substrates. As a result, the homeotropic director configuration is observed within the cell. Under the action of DC electric field, one of the substrates becomes free from the layer of surface active cations, therefore, setting the planar surface anchoring. The latter, in turn, leads to the formation of the hybrid chiral structure. The threshold value and dynamic parameters have been estimated for this process as well as the range of control voltages, which do not allow the electrohydrodynamic instabilities. The twisted hybrid director configuration observed in the experiment has been analysed by means of the simulation of polarisation change of light propagating through the cholesteric layer with asymmetric (planar and homeotropic) surface anchoring on the cell substrates.     

On the influence of porphyrin pi-pi stacking on supramolecular chirality created in the porphyrin-based twisted tape structure

Achiral porphyrin derivatives 1-M form twisted supramolecular assemblies and the pitch of the twisted tape structure can be altered by changing the central metal.     

Transient resonance cars study on the photoisomerization process of bis-dimethylaminoheptamethine perchlorate (BMC)

Photoisomerization of bis-dimethylaminoheptamethine perchlorate (BMC) is investigated by nanosecond time-resolved CARS. During the excitation pulse, the CARS spectrum of a short-lived transient is observed. The kinetic and the spectral behaviour of this transient is consistent with a twisted S₁ configuration being highly populated by simultaneous action of trans—cis and cis—trans photoisomerization. The CARS spectrum due to efficient generation of only one photoisomer configuration is obtained. Results from normal coordinate calculations suggest that a 1,2 mono-cis photoisomer has been generated.