Structure-property relationships of second-order organic nonlinear optical molecules

Chapter I introduces the field of nonlinear optical (NLO) materials, flexible and rigid chromophores, and the incorporation of thiazole and thiophene into nonlinear optical materials. Included in the later is a discussion electronic effects with regard to their effect on the hyperpolarizability.; Computational studies (ZINDO) of several thiophene and thiazole analogs (Chapter 2) of donor/acceptor stilbene compounds establish that the relative orientation of the thiazole subunit in the dipolar chromophore dramatically effects the NLO properties. In the case where the dipole of the thiazole ring opposes the molecular dipole created by the donor/acceptor substituents, diminished hyperpolarizabilities result. The NLO response of heterocyclic analogs of donor/acceptor stilbene derivatives is discussed in terms of the difference in aromatic delocalization energy between phenyl, thiophene, and thiazole, the electronic nature of the heteroaromatic rings, and conformational factors.; Chapter 3 discusses the issue of conformational flexibility in organic NLO materials. In an effort to probe the influence of conformational flexibility on NLO response, we synthesized a series of simple donor-acceptor polyenes that are either conformationally flexible, semirigid, or rigid. For each set of molecules ZINDO calculations predict a larger value of betamu for the conformationally flexible isomer than for the rigid isomer. ZINDO predicts the respective semirigid compounds to have larger hyperpolarizabilities than the rigid chrornophores. Experimental measurements display mixed results.; The fourth chapter describes the synthesis and hyperpolarizability measurements of a series of N-(4-nitrophenyl)amines, where the amine was either a dialkyl amine or a heterocyclic ring. The ring size was changed from three to seven membered, which was shown to effect the hyperpolarizability. The largenst hyperpolarizabilities were measured for compounds with larger heterocyclic rings (≥5-membered) and dialkyl amines. This behavior is discussed in terms of the pyramidalization of the amine nitrogen, conformational issues, and excited state properties.; Chapter 5 describes the measurement of solute dipole moments in dilute solution with a simple three-terminal cell. We describe, in detail, the construction of the cell and thermostating chamber. Molecular dipole moments of acetonitrile in p-xylene and p-nitroaniline in benzene were determined using the Debye equations and capacitance measurements.