Direct evidence of the failure of electric-dipole approximation in second-harmonic generation from a chiral polymer film

Second-harmonic generation from Langmuir-Blodgett films of a polythiophene is strongly influenced by the chirality of the polymer. The polarization dependence of the process cannot be explained in the elec.-dipole approxn. Evidence of contributions beyond elec. dipoles is obtained directly from individual second-harmonic signal

Quadratic Nonlinear Optical Properties of Correlated Chromophores: Cyclic 6,6'-Dinitro-1,1'-Binaphthyl-2,2'-Ethers

The first hyperpolarizability, , of a series of cyclic 6,6¿-dinitro-1,1¿-binaphthyl-2,2¿-ethers has been analyzed with hyper-Rayleigh scattering and electric-field-induced second-harmonic-generation and compared with the absorption data and semi-empirical calculations. The results show the critical dependence of on the conformation of the alkoxy donor and the dihedral angle of the binaphthyl unit

Traveller Specific Drugs Initiative: annual report (November 2000- December 2001): an initiative to promote the inclusion of Travellers in the National Drugs Strategy Building on Experience 2001-2008.

Second-harmonic generation was used as a technique to examine different types of chiral materials. All materials studied showed large circular-difference effects in the 2nd-harmonic response, i.e., the efficiency of the process was different for left- and right-hand circularly-polarized light. Study of various chiral materials showed that a different quant. and qual. response can be expected depending on the compn. and structure. The existence of magnetic dipole contributions to the nonlinearity of those materials is demonstrate

The symmetry of functionalized poly(propylene imine) dendrimers probed with hyper-Rayleigh scattering

In this study, different generations of a poly(propylene imine) dendrimer have been functionalized with second-order nonlinear optical chromophores. The nonlinear optical properties of these macromols. have been investigated using the hyper-Rayleigh scattering technique. The sensitivity of this technique to mol. symmetry is exploited. The measurements show, in a unique way at the mol. level, that the dendrimers in soln. form globular structures at generations with 32 and 64 4-dimethylaminophenylcarboxamide end-groups with restricted mobility of the end-group

Symmetry of functionalized poly(propylene imine) dendrimers probed with hyper-Rayleigh scattering

Hyper-Rayleigh scattering has become the technique of choice for the detn. of the first hyperpolarizabilities of nonlinear optical (NLO) mols. Moreover, by exploiting the sensitivity of this second-order NLO-technique to mol. and supra-mol. symmetry, this technique was upgraded to a powerful spectroscopic tool. The authors did this by probing the symmetry of NLO-functionalized dendrimers, measuring the first hyperpolarizability at different generations. These results are compared with measurements on side-chain NLO-functionalized linear copolymers with different degrees of NLO-functionalization along the polymer backbone. The measurements show, in a unique way at the mol. level, that the dendrimers in soln. form globular structures at generations with 32 and 64 end-groups with restricted mobility of the end-group

Synthesis and (Non)linear Optical Properties of a Series of Donor-Oligopyrrole-Acceptor Molecules,

The Pd-catalyzed cross-coupling reaction involving organostannanes (Stille reaction) is applied to prep. a series of N-t-BOC-protected D-p-A oligopyrroles. After purifn., oligomers with one to four pyrrole units inserted between a 4-nitrophenyl and a 4-methoxyphenyl group are isolated in yields between 20 and 47%. Only minor differences in the linear optical properties are obsd. for the four oligomers. The charge-transfer band around lmax = 365 nm shows a small, unexpected, hypsochromic shift, while the p-p* band around lmax = 285 nm shows a small, expected, bathochromic shift upon elongation of the mol. Their nonlinear optical properties, however, show a surprising proceeding; going from the D-p-A oligomer with one pyrrole unit to that with three pyrrole units, the hyperpolarizability, as measured by hyper-Rayleigh scattering, increases addnl. with the no. of pyrrole units within the oligomer, up to 277 * 10-30 esu in case of the trimer. On the basis of the assumption that both transitions contribute to the hyperpolarizability, a better conjugated D-p-A oligomer with a bithienyl spacer inserted between a 2-(4-nitrophenyl)-5-pyrrolyl and a 2-(4-methoxyphenyl)-5-pyrrolyl group is prepd. analogously. This mol. shows only one combined absorption at lmax = 378 nm for both the charge transfer and the p-p* band, while the hyperpolarizability is as high as 440 * 10-30 esu. These data, showing a very favorable transparency-hyperpolarizability tradeoff, are explained in terms of the contribution of two transitions that are superimpose

Quadratic Nonlinear Optical Properties of Correlated Chromophores: Cyclic 6,6'-Dinitro-1,1'-Binaphthyl-2,2'-Ethers

The first hyperpolarizability, , of a series of cyclic 6,6¿-dinitro-1,1¿-binaphthyl-2,2¿-ethers has been analyzed with hyper-Rayleigh scattering and electric-field-induced second-harmonic-generation and compared with the absorption data and semi-empirical calculations. The results show the critical dependence of on the conformation of the alkoxy donor and the dihedral angle of the binaphthyl unit

Chiral effects in second-order nonlinear optics

The chiral and nonlinear optical properties of polymeric Langmuir-Blodgett films are investigated