The linear and nonlinear optical properties of two metalloporphyrin complexes formed by the complementary coordination of central zinc or magnesium ions to the ligand 5, 10, 15-tri-（p-tolyl）-20-phenylethynylporphyrin are theo- retically investigated by using the analytic response theory at the density functional theory level. The results indicate that the studied complexes present more symmetric geometry structures than the ligand. The charge-transfer states of the two complexes in the lower energy region are all almost degenerate but those of the ligand are well separated. The ratio of the two-photon absorption cross sections of the ligand, zinc-porphyrin and magnesium-porphyrin com- plexes is 1.0：1.5：1.8, demonstrating that the two-photon absorption capability can be greatly increased when the ligand is coordinated with a metal ion. Moreover, several physical micro-mechanisms including electron transitions and in- tramolecular charge-transfer processes are discussed to explore the differences in optical property between the ligand and two complexes.
Aggregation effect caused by the intermolecular hydrogen-bonding interactions on two-photon absorption prop- erties of （E）-4-（2-nitrovinyl） benzenamine molecules is studied at a hybrid density functional level. The geometry optimization studies indicate that there exist two probable conformations for the dimers and three for the trimers. A strong red-shift of the charge-transfer states is shown. The two-photon absorption cross sections of the molecule for certain conformations are greatly enhanced by the aggregation effect, from which a ratio of 1.0：2.6：3.6 is found for the molecule and its dimer and trimer with nearly planar structures. Namely, a 30 or 20 percent increase of the two-photon absorption cross section is observed.
The transport properties of a conjugated dipyrimidinyl-diphenyl diblock oligomer sandwiched between two gold electrodes, as recently reported by [Diez-Perez et al. Nature Chem. 1 635 （2009）], are theoretically investigated using the fully self-consistent nonequilibrium Green＇s function method combined with density functional theory. Two kinds of symmetrical anchoring geometries are considered. Calculated current-voltage curves show that the contact structure has a strong effect on the rectification behaviour of the molecular diode. For the equilateral triangle configuration, pronounced rectification behaviour comparable to the experimental measurement is revealed, and the theoretical analysis indicates that the observed rectification characteristic results from the asymmetric shift of the perturbed molecular energy levels under bias voltage. While for the tetrahedron configuration, both rectification and negative differential conductivity behaviours are observed. The calculated results further prove the close dependence of the transporting characteristics of molecular junctions on contact configuration.
This paper investigates the effect of Lorentz local field correction （LFC） on the propagation of ultrashort laser pulses in a para-nitroaniline molecular medium under resonant and nonresonant conditions by solving numerically the full-wave Maxwell-Bloch equations beyond slowly-varying envelope approximation and rotating-wave approximation. The effect of the LFC is considerably obvious when pulses with large areas propagate in the dense molecular medium. In the case of resonance, the group velocity of the sub-pulses split from the incident pulse along propagation is severely decreased by the LFC, especially for the latest sub-pulse. However, in the case of nonresonance, the influence of the LFC on the temporal evolution of the pulse is less obvious and lacks homogeneity with an increase in incident pulse area, propagation distance and molecular density.
