Molecular hyperpolarizabilities

Large Enhancement of Molecular Hyperpolarizabilities in Dipolar Dendrimers... 

The calculation of for the LD model also indicated an enhancement effect of molecular hyperpolarizability. The value of i g for the LD model was in good agreement with that for the BD one, indicating that the total molecular hyperpolarizability is barely affected by the covalent bonding between azobenzene monomers. We also found that the ab initio values of for the LD model were larger than the ones obtained from the sum of the hyperpolarizabiUty tensors of the individual monomers. In contrast, the ab initio value of for the LD mod-... 

Some quinones, having the ability to form intra- and/or intermolecular hydrogen bonds, exhibit high molecular hyperpolarizability and are third-order nonlinear optical (NLO) materials. Compound 39 has a %(3) of 5 x 10 11 esu at 1.9 pm, and is a third-order NLO material.23 The optoelectric properties of quinoid compounds correlate with their structures in crystals or on thin films.23... 

Moylan CR (1994) Molecular hyperpolarizabilities of coumarin dyes. J Phys Chem 98 ... 

In order to measure molecular hyperpolarizabilities the now standard D-C induced SHG experiment is used (12). Although it would be more suitable to work in the gas phase to minimize molecular interactions, high molecular weights (low vapour pressure) and chemical decomposition processes make it hardly feasible for the molecules of interest. 

Quantum mechanical models at different levels of approximation have been successfully applied to compute molecular hyperpolarizabilities. Some authors have attempted a complete determination of the U.V. molecular spectrum to fill in the expression of p (15, 16). Another approach is the finite-field perturbative technique (17) demanding the sole computation of the ground state level of a perturbated molecule, the hyperpolarizabilities being derivatives at a suitable order of the perturbed ground state molecule by application of the Hellman-Feynman theorem. 

The large molecular hyperpolarizability of the merocyanine chromophore (4,5) and the highly polar environment of the quasicrystals has prompted studies of the second order nonlinear optical properties of these materials (6). 

For obtaining the information on fabrication of noncentrosymmetric LB films with highly efficient second-order optical nonlinearity, six azobenzene-linked amphiphiles were synthesized as a model compound, and their molecular hyperpolarizabilities (3, monolayer-formation at the air-water interface, and molecular orientation and second-order susceptibilities of the azobenzene-linked amphiphiles LB films were evaluated. The molecular structures of the azobenzene-linked amphiphiles are shown in Fig.2. 

Molecular hyperpolarizabilities p of the azobenzene-linked amphiphiles were estimated using the following equation derived from the two-level model [3] ... 

Table 1. Molecular hyperpolarizabilities P of azobenzene-linked amphiphiles used in this study. 

Stark effect measurements for determination of molecular orientation and second-order molecular hyperpolarizability... 

Evaluation of second-order molecular hyperpolarizability using the quadratic Stark effect... 

The non-linear optical properties of a material are evaluated by measuring (using techniques from the field of physics) its molecular hyperpolarizability coefficient (3. 

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