Date of Award

12-1-2004

Degree Type

Dissertation

University or Center

Clark Atlanta University(CAU)

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Professor Xiu Ren Bu

Abstract

Photoresponsive molecules have a broad range of potential applications, for example in optical, energy, and biomedical technologies. Fluorophores and second order nonlinear optical (NLO) chromophores are photoresponsive molecules used as signaling materials and frequency doublers or electro-optical modulators, respectively.

The research presented here describes the synthesis, characterization, and potential applications of a group of highly fluorescent molecules and NLO chromophores containing benzene, imidazole and thiophene rings. Methyl, methoxy, and dimethylamino groups were used as electron donor groups while formyl and nitro groups were used as electron acceptors.

The fluorescence properties of a series of dyes containing donor groups and a formyl group attached to a thiophenyl ring were investigated. X-ray structural determination revealed a steric crowding, which causes a molecular twist in the ground state. The fluorescence quantum yield for these fluorophores was found in the range of0.004-1.0. It was determined that these fluorescent molecules emit light from a non-polar locally excited (LE) state and a polar intramolecular charge transfer (ICT) excited state. The dye containing the dimethylamino group was characterized by dual fluorescence in moderate polar solvents. The excited state dipole moments and excited state lifetimes were found to increase as the strength of the donor group increases. A linear correlation was obtained for the Stokes shift versus the solvent polarity parameter ET(30) and the Hammett's constant σ+. Solvatochromic studies revealed a solvent polarity dependence on fluorescence properties.

Macromolecules containing selected fluorophores were synthesized. The fluorescence quantum yield of the macro-systems was found to be lower than the respective monomer. A series of NLO chromophores having donor groups (i.e., methyl, methoxy, and dimethylamino) and nitro as acceptor were synthesized. They were studied in terms of the nonlinear optical coefficient 3u and thermal stability. The chromophores containing a thiophenyl stilbene conjugation showed superior NLO properties and moderate thermal stability in comparison with their respective analogs. The synthesis of macromolecules containing selected chromophores is also reported.

Finally, preliminary synthesis and characterization of other potentially photoresponsive compounds are presented.

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