Ground-state dipole moments measurements

In this study we have described theoretical calculations, syntheses, optical spectra, ground-state dipole moment measurements, and measurements of molecular second-order hyperpolarizability coefficients (/J) for new stilbene and azobenzene derivatives containing a methylsulfonyl group as the electron acceptor. We have shown that theoretical calculations can be used to predict the ratio of molecular hyperpolarizabilities between similar compounds, and that these gas phase calculations underestimate /J, probably as a result of the valence basis set used in the calculations. 

Attention should be paid to the fact that the electron motion from a donor to an acceptor or within spread-conjugated ion-radicals generates measurable electromagnetic radiation. In other words, there is one specific way to reveal intramolecular electron motion or intermolecular electron transfer in charge-transfer complexes. To probe electron transfer in this manner, the only fundamental requirements are that the molecule can be oriented in the external magnetic field. This takes place most easily if the species considered has a ground state dipole moment. On photoexcitation, there... 

The second experimental measure of the orientation of the dipole moment in the ground state of the bases was made by Seibold and Labhart405 for uracil and thymine. The direction of the ground state dipole moment with respect to the transition moment in the lowest excited singlet state has been determined from the influence of an... 

This paper summarizes the theoretical analysis of some new molecules with methylsulfonyl group as the electron acceptor group, describes the syntheses of new stilbene and azobenzene systems, and presents the measurements of their optical spectra, ground-state dipole-moments, and molecular hyperpolarizability coefficients, p. We compare theoretical and experimental results and comment on the potential usefulness of these chromophores as components for NLO materials. The incorporation of sulfonyl-containing chromophores into polymers, and the NLO properties of the resulting materials, will be discussed in our forthcoming paper (9). 

The measurement of ground-state dipole moments may help to establish the validity of the theoretical calculations. We measured two representative compounds, X, and XI (see below), where diallyl derivatives were used to increase solubility in nonpolar solvents (e.g., CC14). 

We have also measured the ground-state dipole moment of DANS (VII), in CHCI3, and obtained the value 7.6 D. This, indeed, was an encouraging result since it further supported the credibility of our molecular design approach that was developed to speed up the search for new NLO materials. 

Dipole moments have been measured in the ground and excited states for three derivatives of compound (1) <83CPL58>. Ground-state dipole moments are shown in Figure 4. The ground-state dipole moment of the parent structure (1) has been found experimentally to be 4.87 x 10-30 C m (1.46 D) <81JPC3181>. 

Also, Aaron, Parkanyi and co-workers ([25] and references therein) measured the ground-state dipole moments of BPHT derivatives (compounds 2-8) in dioxane with a dipole meter at 20 °C (Table 5). While the dipole moments of compounds 5 and 8 were lower than that of phenothiazine (1), the remaining derivatives displayed higher ground-state dipole moment values, ranging between 3.4 and 5.53 D. 

W.E. Ernst, S. Kindt, K.P.R. Nair, and T. Torring, Determination of the ground state dipole moment of CaCl from molecular-beam laser-microwave double resonance measurements, Phys.Rev.A 29 1158... 

In this next section the dipole magnitude and directionality from MM3(2000) is compared to results obtained by MM3(96), Hartree-Fock and Mdller-Plesset minimized structures (calculated using GAUSSIAN94),77 as well as experimental dipole moment measurements.78 For the molecular mechanics geometry optimizations, full matrix energy minimizations were carried out, and ground state structures were verified by the vibrational... 

The experimental data reported in the Table for gas phase have been extracted from measurements in dioxane solution by applying the Onsager reaction field model to eliminate the solvent effect [37], By contrast, the cyclohexane experimental dipole moments have been obtained from those reported in Ref. [37] re-including the proper reaction field factors. Once recalled these facts, we note that the observed solvent-induced changes on both ground and excited state dipole moments are quantitatively reproduced by the calculations. 

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