Hologram recording and the electrooptic effect in azobenzene derivative polymers and azobenzene derivative-cobalt polycomplexes

The electrooptic effect and the kinetics of recording/erasing the hologram of a plane wavefront in films of the 4-methacryloxy-(4′-carboxy-3′-oxy)azobenzene-cobalt polycomplex and 4-carboxy-3-oxy-3′-carboxy-4′-oxyazobenzene-cobalt polymer are studied. The electrooptic properties of the films depend on the reorientation of the polarized-light-induced dipole moments of azobenzene groups in an external electric field and, eventually, on forces acting on the azo groups and metal ions. It is found that the characteristic times of the electrooptic effect and holographic grating formation are longer in the polymer with an intrachain coordination of the metal ions.     

共轭高分子链中极化子间相互作用对电荷迁移率的影响

基于综合考虑了电子与声子以及电子与电子相互作用的理论模型,采用数值方法计算了在外电场作用下共轭高聚物分子中电荷的迁移率,讨论了大小极化子共存并相互作用对分子链内电荷迁移率的影响。研究发现,电荷迁移率明显受大小极化子的载荷性质的影响,当大小极化子具有相同电性时,在低电场范围内,分子内电荷迁移率由大极化子运动性质主导,而在高电场范围内,分子内电荷迁移率由小极化子主导;另一方面,当大小极化子具有相反电性时,电荷迁移率只由大极化子运动性质主导,与电场强度无关。此外,还讨论了电子与电子相互作用对电荷迁移率"的影响。     

Anisotropic models of polymer ferroelectrics

The phase transitions to an ordered state in three-dimensional polymer systems that consist of flexible and rigid segments with intrachain and interchain orientational-deformational dipole interactions are considered. The statistic properties of the proposed models correspond to the Gaussian and spherical approximations that are used to describe the behavior of anisotropic Heisenberg ferroelectrics and ferromagnets. In the three-dimensional models under consideration, there exists a critical point T _c where a secondorder phase transition from an isotropic state to a state with long-range orientational order occurs. The laws of variation in the temperature T _c as a function of anisotropy of the interactions are established by analytical methods. The temperature dependences of the long-range dipole order parameter for a given chain bending are calculated and the results are compared with the experimental data obtained by the piezoelectric pressure step (PPS) method for thick ferroelectric PVDF and P(VDF-TrFE) polymer films.     

Phase diagram of the frustrated spin ladder with the next nearest intrachain couplings

By the density matrix renormalization group method, the phase diagram of the frustrated spin-1/2 ladder with the next nearest intrachain and ferromagnetic interchain couplings is obtained. According to our results, the two-rung entanglement is shown to be more sensitive than order parameters for determining phase boundary in such a frustrated spin ladder model. Furthermore, the additional next nearest intrachain coupling is found to enhance the intermediate columnar dimerized phase evidently.     

The effect of intermolecular interactions on photoluminescence of a porphyrin side-chain polymer

Photoluminescence properties and exciton decay dynamics in a porphyrin side-chain polymer, poly[porphyrin acrylate- acrylonitrile (abbreviated p[(por)A-AN]), have been investigated by femtosecond time-resolved photoluminescence spectroscopy. All the luminescences of p[(por)A-AN] films are due to the emissive decay of the photoexcited singlet excitons in the porphyrins. The luminescence efficiencies and lifetimes are increased for samples from pure films to dilute blend films. However, they are increased as the intrachain concentration of the porphyrin sidechain groups is decreased. The intrachain rotation motions of porphyrin sidechain groups result in the initial ultrafast luminescence decays, which are much faster than those due to the interchain interactions. All the samples show no significant red-shift and broadening of the transient luminescence spectra. The interchain and intrachain nonradiative exciton relaxation processes may play an important role in the luminescence dynamics in the p[(por)A-AN] films. The possible origin of different intrachain and interchain dynamic behaviours in p[(por)A-AN] films is discussed.     

Gap Caused by Strong Pairing in the Ladder Model of DNA Molecules

By directly diagonalizing the Hamiltonian of the ladder model of deoxyribonucleic acid （DNA） molecules, the density of states is obtained. It is found that DNA behaves as a conductor when the interchain hopping is smaller than twice the intrachain one, otherwise, DNA behaves as a semiconductor.     

共轭聚合物中链内无序效应对极化子输运的影响

基于扩展的Su-Schrieffer-Heeger紧束缚模型, 利用非绝热动力学方法研究了链内无序效应对共轭聚合物中极化子输运机制的影响. 研究发现, 极化子的输运由外加电场和链内无序效应共同作用的结果所决定. 在一般情况下, 链内无序效应不利于极化子的输运, 但随着电场强度的增大, 无序对极化子输运的影响减小. 关键词： 共轭聚合物 极化子输运 链内无序     

High intrachain hole mobility on molecular wires of ladder-type poly(p-phenylenes)

We have studied the high-frequency (34 GHz) mobility of positive charge carriers on isolated ladder-type polymer chains in dilute solution. We find that the high-frequency mobility is limited by the chain ends on chains as long as 35 monomers. The intrachain motion of charge carriers can be described by one-dimensional diffusion between infinitely high reflecting barriers, representing the chain ends. Our data indicate that the intrachain mobility for ladder-type polymer chains is close to 600 cm(2)/V s. With this high mobility the ladder-type polymer is a promising candidate for future use as an interconnecting wire in molecular electronics.     

On the state space of the dipole ghost

A particular representation of SO(4, 2) is identified with the state space of the free dipole ghost. This representation is then given an explicit realization as the solution space of a 4th-order wave equation on a spacetime locally isomorphic to Minkowski space. A discrete basis for this solution space is given, as well as an explicit expression for its SO(4, 2) invariant inner product. The connection between the modes of dipole field and those of the massless scalar field is clarified, and a recent conjecture concerning the restriction of the dipole representation to the Poincaré subgroup is confirmed. A particular coordinate transformation then reveals the theory of the dipole ghost in Minkowski space. Finally, it is shown that the solution space of the dipole equation is not unitarizable in a Poincaré invariant manner.     

Temperature dependence of the energy of point dipole interaction with the surfaces of solids

The effect of temperature on the energy of the interaction of mirror image forces of a point dipole with the surfaces of metals and dielectrics is considered. It is shown that as a dipole approaches a surface and/or the temperature falls, the chaotic motion of the dipole axis becomes more and more ordered, establishing the conditions for the dependence of the dipole interaction energy not only on the distance to the surface but also on the temperature.     

The solution of a wedge disclination dipole interacting with an annular inclusion and the force acting on the disclination dipole

The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole centre is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force increases （or the attraction force reduces） with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special eases.     

聚(9,9-二辛基芴)和聚(9,9-二辛基芴-共-苯并噻二唑)的光物理特性的理论和实验研究

通过比较分析聚(9,9-二辛基芴)(PFO)和聚(9,9-二辛基芴-共-苯并噻二唑)(F8BT),对半导体聚合物的光物理特性进行了系统研究. 量子化学计算显示,苯并噻二唑单元的引入促进了链内电荷转移(ICT),调节了聚合物的电子跃迁机制. 瞬态吸收测定表明,在单分散系统中的受激PFO衰减时主要表现为链内激子弛豫.在F8BT溶液中,ICT状态出现,并参与到激发态的弛豫过程中. 凝聚相中PFO和F8BT的弛豫过程加速和显示了在高激发强度下具有显著的激子湮灭行为. 在相同的激发强度下,F8BT的平均寿命长于PFO,有助于实现良好的电荷离域.     

Effects of interchain coupling on photoexcitation in two coupled polymer chains in the presence of an electric field

Within an extended Su-Schrieffer-Heeger model including interchain interactions and the extended Hubbard model (EHM), the dynamical relaxation of photoexcitations in the presence of an external electric field is investigated using a nonadiabatic evolution method. Under the action of the interchain interactions both intrachain excitons and interchain excitons are generated after photoexcitation in two coupled polymer chains. Our results show that the field required to dissociate the excitons depends sensitively on the strength of the interchain coupling. As the interchain coupling strength increases, the dissociation field decreases. By analyzing the relation between the yield of intrachain and interchain excitons and the interchain coupling strength, we explain the dependence between the dissociation field and the strength of the interchain interactions. The theoretical results are expected to provide useful predictions concerning which polymers with properly strong interchain interactions are likely to be most suitable for use in organic solar cells.     

Coulomb effects on the Peierls transition

The influence of the intrachain Coulomb interactions on the Peierls transition is examined. The change of the form of the electronic polarizability at twice the Fermi wavevector, to a power law divergence in the presence of Coulomb interactions, is found to enhance the mean field transition temperature for the Peierls transition.     

The Orientation of the Phosphorescence Dipole Moment of Erythrosine B Within Its Molecular Frame

For an unequivocal interpretation of time-resolved phosphorescence depolarization measurements on dye molecules in biophysical systems, the orientation of the transition dipole moments within the frame of the dye has to be known. The goal of this work is to find the orientation of the phosphorescence dipole moment of erythrosine B within its molecular frame. To this end, we first determine four difference angles, exciting a molecule in two of its absorption bands and measuring the fluorescence and phosphorescence anisotropy for each excitation wavelength. The next step is to position the transition dipole moments within the molecular frame, combining the results of angle-resolved fluorescence depolarization measurements with the measured difference angles. It is shown that the phosphorescence dipole moment is tilted out of the plane of the molecule. Additionally, we find that the phosphorescence dipole moment is located above the fluorescence dipole moment and not above the absorption dipole moment. This induces an extra difference angle between the absorption and the phosphorescence dipole moments which in the past has been interpreted erroneously as a larger tilt out of the plane of the molecule.     

Dipole effects and the work functions of the single crystal LaB6

Both the interior dipole structure normal to the polar surface of a crystal and any dipole layer at the surface itself contribute to the surface work function. For LaB₆, the structures of the unreconstructed (100), (110) and (111) faces or the reconstructions believed to characterize the (110) and (111) surfaces would produce dipole layers and differences in work function among these surfaces which are at least an order of magnitude greater than the differences which have been measured. Modification in ionic charge at sites making up the outermost surface dipole layers can markedly affect the dipole contribution to the work functions and it is argued that such charge modification may occur as a general phenomenon in ionic crystals.     

Subwavelength displacement of the far-field image of a radiating dipole

The field lines of the Poynting vector for light emitted by a dipole with a rotating dipole moment show a vortex pattern near the location of the dipole. In the far field, each field line approaches a straight line, but this line does not appear to come exactly from the location of the dipole. As a result, the image of the dipole in its plane of rotation seems displaced. Secondly, the image in the far field is displaced as compared with the image of a source for which the field lines run radially outward. It turns out that both image displacements are the same. The displacements are of subwavelength scale, and they depend on the angles of observation. The maximum displacement occurs for observation in the plane of rotation and equals lambda/pi, where lambda is the wavelength of the light.     

Physical model and the associative memory of a cytoskeleton microtubule as a system of dipoles

A physical model of the conformational degrees of freedom of a cytoskeleton microtubule represented as a system of interacting dipoles is elaborated, characteristic physical quantities are estimated, and a phase diagram of the ferroelectric state of the microtubule at T = 0 is constructed. The presence of frustrated couplings J _ij between the dipoles appears to be the most important feature of the disordered dipole system of the microtubule, owing to which the ground state of the dipole system splits into a large number of lower energy states. The dynamics of the dipole system is determined by the relaxation of the dipole-dipole interaction energy. After the dipole system has evolved to its final state, the input image is associated with one of reference images stored earlier; hence, the dipole system of a microtubule can be viewed as a distributed system with associative memory.     

Direct determination of the sign of the NO dipole moment

We report a novel approach for determining the sign of permanent dipole moments, using nitric oxide [NO(v=0)] as an example. State-selected NO (j=|m|=|Omega=1/2) molecules are focused using a hexapole and oriented in a strong dc electric field. The angular distributions of ionic fragments resulting from extreme ultraviolet single-photon and multiphoton dissociative ionization at 400 and 800 nm are measured and indicate that the dipole moment is negative (corresponding to N-O+). The experiments thus rule out an error in the sign of the dipole of NO as the possible source of a remarkable discrepancy between previous theoretical and experimental work on orientation effects in bimolecular collisions involving oriented NO.     

Influence of damping on the excitation of the double giant resonance

We study the effect of the spreading widths on the excitation probabilities of the double giant dipole resonance. We solve the coupled-channels equations for the excitation of the giant dipole resonance and the double giant dipole resonance. Taking Pb+Pb collisions as example, we study the resulting effect on the excitation amplitudes, and cross sections as a function of the width of the states and of the bombarding energy. Received: 13 July 1999