Synthesis and characterization of a family of nonlinear optical materials

The development of nonlinear optical (NLO) materials represents an exciting field with applications in areas such as optical signal processing and coherent laser light generation. Second-order NLO chromophore containing materials are being used as frequency doublers or electro-optical modulators while third order NLO chromophores are being designed with large two-photon absorption coefficients for upconverted lasing and imaging applications.; This dissertation describes the synthesis and characterization of a group of NLO chromophores containing aromatic heterocyclic rings as {dollar}pi{dollar}-electron donors, acceptors, and bridging groups. Thiophene, 3,4-ethylenedioxythiophene (EDOT), and diphenyl amine were used here as the electron donor groups while pyridine was used as the electron acceptor. Fluorene ring units were incorporated as aromatic {dollar}pi{dollar}-electron bridging groups with n-decyl or ethyl chains attached at the C-9 position of the fluorene in order to promote solubility in common organic solvents.; One asymmetrical chromophore was made via a three step technique in which a thiophene- and pyridine-propargyl amine reacted with a 2,7-(bisallylbromide)fluorene to form a salt. The bonds underwent a Stevens rearrangement after the addition of a base and finally were thermally cyclized to create a new phenyl ring. Consequently, a new chromophore was made resulting in a molecule with a thiophene and pyridine group separated by four phenyl rings.; Other chromophores were made with carbon-carbon bond formation via a Stille coupling process. Thiophene, EDOT, and pyridine rings were functionalized with tributyltin groups, and the resulting molecules coupled with halogenated di-n-decyl-fluorenes. Two asymmetrical chromophores were made using a thiophene and pyridine as the {dollar}pi{dollar}-electron donor and acceptor rings, respectively, and either one or two fluorene groups as the {dollar}pi{dollar}-electron bridge. Three symmetrical chromophores were also made in the same manner to yield molecules with thiophene, EDOT, or pyridine rings on both sides of a single fluorene group. Additionally, the conjugation length between the pyridine groups of the symmetrical chromophore was extended by two double bonds by reacting 4-vinylpyridine and a dibromofluorene via a Heck reaction.; A third class of chromophores was made using diphenylamine and pyridine as the {dollar}pi{dollar}-electron donor and acceptor groups, respectively, and di-n-decyl- and diethyl-fluorene as the bridging group. The electron withdrawing properties of the pyridyl group was also enhanced by quarternizing it with methyl iodide to form the iodide salt and then performing an ion exchange with sodium tetraphenylboron.; Finally, a monomer was prepared in a six step scheme by synthesizing a diphenylamine with methoxy groups, coupling that at the 2-position of diethylfluorene, converting the methoxy to hydroxy groups, and coupling 4-vinylpyridine to the 7-position on the fluorene via the Heck reaction. The monomer was then successfully polymerized with 4,4{dollar}spprime{dollar}-difluorodiphenyl sulfone using two different condensation techniques.; Electric field induced second harmonic generation (EFISH) as well as the two-photon absorption characterization of these materials were also carried out and are reported.; One material prepared in this thesis (compound 65), AF-50) was found to have the largest two-photon absorption cross section of any organic chromophore to date and shows much promise for a variety of NLO applications.