The magnetic dipole (M1) and electric quadupole (E2) responses of two-dimensional quantum dots with an elliptic shape are
theoretically investigated as a function of the dot deformation and applied static magnetic field. Neglecting the electron-electron
interaction we obtain analytical results which indicate the existence of four characteristic modes, with different B-dispersion of their energies and associated strengths. Interaction effects are numerically studied within the time-dependent
local-spin-density and Hartree approximations, assessing the validity of the non-interacting picture.
Received 29 November 2001 Published online 6 June 2002 相似文献
Regioselectivity of the photochemical [2 + 2] cyclo-addition of triplet carbonyl compounds with a series of ground state electron-rich
and electron-poor alkenes, the Paterno-Büchi reaction, is studied. Activation barriers for the first step of the triplet reaction
are computed in the case of the O-attack. Next, the observed regioselectivity is explained using a series of DFT-based reactivity
indices. In the first step, we use the local softness and the local HSAB principle within a softness matching approach, and
explain the relative activation barriers of the addition step. In the final step, the regioselectivity is assessed within
the framework of spin-polarized conceptual density functional theory, considering response functions of the system’s external
potential v, number of electronsN and spin numberNs, being the difference between the number ofα andβ electrons in the spin-polarized system. Although the concept of local spin philicity, introduced recently within this theory,
appears less suited to predict the regioselectivity in this reaction, the correct regioselectivity emerges from considering
an interaction between the largest values of the generalized Fukui functionsfss on both interacting molecules. 相似文献
Concentration quenching of the triplet state (CQTS) of a number of Pd-porphyrins in toluene is investigated. Based on an analysis
of experimental results, a conclusion is drawn that such quenching proceeds via formation of exciting complexes from molecules
in the ground and triplet states (TS). From a small value of decay rate constants of the complexes it follows that these complexes
are triplet excimers but not complexes due to collision. It is established that by increasing the concentration of porphyrins
the maxima of their phosphorescence bands shift toward large wavelengths by a value of up to 3 nm and the bands, as a consequence,
broaden by 5–7 nm. The formation of excimers is explained by enhancement of solvophobic dispersion interactions of molecules
in the TS. Relatively small changes in the phosphorescence spectra upon formation of excimers are attributable to these interactions.
The magnitude of dipole-dipole interaction of molecules in the TS is insignificant since the dipole moment of the T↭S transition
is small. On the basis of consideration of the oxidation-reduction and energy characteristics of the compounds, it is shown
that the interaction with charge transfer in the case of the CQTS of Pd-porphyrins is inefficient.
Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072,
Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 857–863, November–December, 1998. 相似文献
Conjugated polymer nanoparticles based on poly[9,9‐bis(2‐ethylhexyl)fluorene] and poly[N‐(2,4,6‐trimethylphenyl)‐N,N‐diphenylamine)‐4,4′‐diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2′‐bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye‐coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle‐dye hybrids. It is proposed that the excited state electron transfer from the electron‐rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed‐electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir‐based triplet emitting dye as the guest.
在B3LYP/6-311++G(d,p)水平对白藜芦醇顺反异构体及第一三重激发态进行了结构优化、频率计算和自然键轨道(Natural Bond Orbital,NBO)分析.在MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)水平比较了白藜芦醇顺反异构体的能量.反式白藜芦醇整个分子呈平面结构,顺式白藜芦醇两苯环之间存在约30o扭角.第一三重激发态中两苯环几乎处于互相垂直的关系,C7-H5与C8-H6键也是几乎互相垂直的关系.顺式和反式白藜芦醇C7-C8的σ键成键情况分别为sp1.53-sp1.53和sp1.59-sp1.60,C7与C8各自提供p轨道形成π键,即形成C7=C8双键.三重态中,C7-C8的成键情况为sp1.92-sp1.89,没有p-pπ键,C7、C8均还有一个2p轨道未参与杂化,NBO分析证实C7、C8的各自剩下的2p轨道均几乎独立形成了高能量的反键轨道,分别垂直于单羟基和双羟基苯环,C7-C8键长明显长于白藜芦醇顺反异构体.顺式白藜芦醇比反式白藜芦醇的自由能高约1.3-2.5 kcal/mol,反式构型是热力学稳定构型.含时密度泛函方法(Time-Dependent Density Functional Theory,TD-DFT)方法,B3LYP/6-311++G(d,p)水平计算得反式和顺式白藜芦醇最强紫外吸收峰分别在330 nm和319 nm. 相似文献
Energy up-conversion is the process by which two absorbed photons are converted in one photon of higher energy. Such a process can be conveniently performed by low-power excitation through sensitized triplet-triplet annihilation and it is now an emerging technique with possible applications in different fields, including photovoltaic devices and bioimaging. 相似文献
Exciton-coupled charge-transfer (CT) dynamics in TiO(2) nanoparticles (NP) sensitized with porphyrin J-aggregates has been studied by femtosecond time-resolved transient absorption spectroscopy. J-aggregates of 5,10,15-triphenyl-20-(3,4-dihydroxyphenyl) porphyrin (TPPcat) form CT complexes on TiO(2) NP surfaces. Catechol-mediated strong CT coupling between J-aggregate and TiO(2) NP facilitates interfacial exciton dissociation for electron injection into the conduction band of the TiO(2) nanoparticle in pulse width limited time (<80 fs). Here, the electron-transfer (<80 fs) process dominates over the intrinsic exciton-relaxation process (J-aggregates: ca. 200 fs) on account of exciton-coupled CT interaction. The parent hole on J-aggregates is delocalized through J-aggregate excitonic coherence. As a result, holes immobilized on J-aggregates are spatially less accessible to electrons injected into TiO(2) , and thus the back electron transfer (BET) process is slower than that of the monomer/TiO(2) system. The J-aggregate/porphyrin system shows exciton spectral and temporal properties for better charge separation in strongly coupled composite systems. 相似文献