Heavy Atom Effect on the First Hyperpolarizabilities of Squaric Acid Homologues Studied by Ab Initio and DFT Methods

We have calculated the first hyperpolarizabilities of four squaric acid homologue molecules: 3,4-dithiohydroxy-3-cyclobutene-1,2-dione (OSSQ), 3,4-dithiohydroxy-3-cyclobutene-1, 2-dithione (SSSQ), 3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone (SeSSQ) and 3,4-dithiohydroxy- 3-cyclobutene-1,2-ditellurone (TeSSQ). The correlation effect was investigated at the second-order Mller-Plesset (MP2) perturbation and density functional theory (DFT) levels. The frequency disper- sion and solvent effect were considered to compare the theoretical values with the experimental observations. Based on all of these studies, it is worthy to point out that the heavy atom effect dis- covered for furan homologues is an influence on the first hyperpolarizabilities of squaric acid homologues.

Theoretical Studies on the First Hyperpolarizabilities of One-dimensional Donor-bridge-acceptor Chromophores and New Applications of BLA in Determining Molecular First Hyperpolarizabilities

We present a quantum-chemical analysis of the relationship between the bond length alteration （BLA） and the static first hyperpolarizability of a series of one-dimensional （1D） chromophores with donor-bridge-acceptor （D-B-A） structures. The calculated results show that the parameter BLA can be considered as an indicator to evaluate the molecular first hyper- polarizability. Along the direction of molecular ground-state dipole moments, the evolutions of BLA can be classified into three categories： the first is a non-monotonic line, which represents most chromophores; the second is monotonic increasing; and the third, contrarily, is monotonic decreasing. On the whole, the first hyperpolarizabilities of these studied chromophores are the monotonic functions of BLA along the direction of dipole moments. Therefore, the first hyperpolarizability of these 1D chromophores can be preliminarily evaluated in terms of the development of BLA without a rigorous computation. In other words, one can roughly estimate the relative magnitude of the first hyperpolarizability according to the optimized geometry.

Theoretical Studies on the First Hyperpolarizabilities of One-dimensional Donor-bridge-acceptor Chromophores

The ground-state dipole moments and second-order nonlinear optical （NLO） properties of a series of one-dimensional （1D） chromophores with donor-bridge-acceptor （D-B-A） structures have been investigated by using the second-order MФller-Plesset （MP2） and density functional theory （DFT） methods with the basis set of 6-31＋G（d）. According to the calculated results, the relationship between the molecular static first hyperpolarizability （βμ） and the directions of electron transition has been summarized. In terms of the sign of βμ, these 1D organic chromophores were classified into two categories： type Ⅰ with negative βμ and type Ⅱ bearing positive βμ. The analyses show that the remarkable difference of the first hyperpolarizabilities between Ⅰ and Ⅱ chromophores is associated mainly with the electrostatic interaction between terminal groups and the transport electrons in excited states. Moreover, different from the popular viewpoint, the obtained results also show that most of this series of 1D D-B-A molecules are more charge-separated in the ground states than in the excited states. As a whole, this theoretical investigation, to some extent, can be considered as a useful reference in designing the NLO chromophores with large first hyperpolarizabilities.

Lithium Salt of NH_2-substituted Graphene Nanoribbon with Twofold Donor-acceptor Framework: Large Nonlinear Optical Property

Based on graphene, a new class of second-order nonlinear optical（NLO） material, the lithium salt of NH2-substituted graphene nanoribbon with the twofold donor（D）/acceptor（A） mode, was reported. Eight stable 2Li-2NH2-GNR lithium salts, especially cis lithium salts, display considerably large β0 values. The combination of NH2-substituting and cis Li-doping makes β0 greatly increased from 0（GNR） to 1.2×105―2.9×105 a.u.（cis-2Li- 2NH2-GNRs）. Our largest β0 value（2.9×105 a.u.） for cis-2Li-1,3-2NH2-AGNR is comparable to the record value of 1.7×105 a.u. for a long donor-acceptor polyene.

Second-order Nonlinear Optical Properties of a Series of Az-ulene Derivatives

The first hyperpolarizabilities of a series of novel azulenic-barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolariza-bilities of chromophores holds the same tendency as the experimental results. In addition, the static first hyperpo-larizability 0 of molecules was calculated by means of the Sum-Over-States (SOS) expression and the two-level formula respectively. The results show that these molecules possess large static first hyperpolarizabilities and the 0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the 0 value.

Structures and Nonlinear Optical Properties of Lithium-adsorbed Polycyclic π-Conjugated Pentacene Systems

Structures and nonlinear optical（NLO） properties of eleven new Lin-Pm（n=1-5） species were investigated in detail with the help of ab initio computation, in which one to the maximum five Li atoms are doped over the polycyclic π-conjugated pentacene. These Li-doped pentacene systems exhibit large adsorption energies（ca. 107.0--141.3 kJ/mol） and considerable first hyperpolarizabilities（even up to 4.1×10^4 a.u.）, where the number of Li atoms, the doping site, and the distance between the neighboring Li atoms have important impacts on the flo value. In the doped pentacene systems with less Li atoms（one or two）, the improvement of β10 value can be attributed to the simple transfer of the charge from Li atom to pentacene. Differently, doped more Li atoms（three to five） can cause not only charge transfer but also excess electron, and this cooperation can endow the doped systems with the much larger first hyperpolarizabilities. These fascinating findings are advantageous for the design of new NLO materials based on the intriguing polycyclic π-conjugated systems.

Finite field study on nonlinear optical properties of substituted ketene N,S-acetals

The nonlinear optical properties of title compounds calculated by AM1/finite field (AM1/FF) approach are discussed based on their crystal parameters. The origins of large molecular first hyperpolarizahilitiesβ and good transparency of the compounds are explained well through the aromatic character enhancement in the excited state and the short conjugation length in the ground state. Results show that the difference ofβ values obtained by two experimental methods (Solvatochromic and Hyper Rayleigh Scattering) is due to the molecular quasi-two-dimension character and the octupolar components’ contribution. The calculation has also demonstrated that the change ofγ xxx caused by different donor substituents is linearly related with the Hammett substituent constant σ+.