Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The spectroscopic and photochromic characteristics of triphenylformazan and its derivatives were investigated. These derivatives were formed by adding substituents to the phenyl group attached to the carbon atom of the formazan ring or by replacing this phenyl group with a naphthyl group. Studies of the effect of the concentration, substituent, solvent and temperature on the absorption spectra of triphenylformazan were made. Molecular mechanics calculations were performed to generate two different geometries of triphenylformazan that were used in CNDO calculations to assign the electronic transitions observed in the absorption spectra. In contradiction to what was stated in earlier investigations, the results of this work indicate that a second isomer of triphenylformazan is not formed only by irradiation but the two chelated forms exist in an equilibrium mixture. These two forms have different geometries and absorb at different wavelength in the visible region of electromagnetic spectrum. The results of the determinations of the effect of alcohols on the absorption spectra of triphenylformazans with an electron withdrawing group as O('-) or Cl lead to a better understanding of the structure of these derivatives. The mechanism of stabilization of the formazan ring in these derivative with increasing temperature is also suggested by the results obtained in this investigation. The acidity of alcohols has a strong influence on the equilibrium between the chelated (or red or closed) form and the unchelated (or yellow or open) form of the ortho-hydroxy derivative. Resonance Raman and picosecond laser spectroscopy experiments are proposed to confirm the conclusions reached in this investigation.

Pages

233

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