Date of Award

6-1974

Document Type

Open Access

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Abstract

A comparison was made between spectral properties of several atomatic esters of 9- anthroic acid (9- COOAR) and the methyl ester (9-COOMe). The spectral properties observed were absorption spectra, fluorescence quantum yields (Øf) and Stokes shifts. Although all of the ester absorption spectra showed anthracene-like structure, the aromatic ester spectra were clearly more diffuse than the 9-COOMe spectrum. Certain electron delocalization pathways are available to 9-COOAR but not to 9-COOMe, thereby allowing greater carboxyl group-ring interaction for 9-COOAR, resulting in increased spectral diffuseness relative to 9-COOMe. Data are presented which show that the electronic absorption spectra of these esters are more sensitive and reliable indicators of carboxyl group-ring interaction than the infrared spectra. Excited state electron delocalization pathways available to 9-COOAR but not to 9-COOMe account for the greater Stokes shifts observed for 9-COOAR. The ¢f values for the phenyl, para-bromophenyl and methyl esters are the same within experimental error. No heavy atom effect was observed for the p-bromophenyl ester, which suggests that the excitation is localized on the anthroate portion of the molecule. Øf values for the p-nitrophenyl, β-naphthyl and p-methoxyphenyl esters are considerably less than Øf for 9-COOMe. The reduced Øf may be due to enhanced intersystem crossing and, for the latter two esters, high rates of photoreactivity may lower Øf values. Heavy atom quenching experiments were performed on 9-COOMe and several anthracene derivatives. The relatively inefficient quenching observed for 9-COOMe suggests that ∆ES1 – TX is larger for 9-COOMe than for anthracene. Quantum yields, fluorescence lifetimes and molar absorptivities were measured for 1-methyl anthroate (1 - COOMe) in cyclohexane and isopropanol. A smaller Øf for 1-COOMe was observed in the less polar solvent, which is the inverse of the solvent effect observed for Øf of 9- COOMe.

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