Chemistry and Chemical Biology ETDs

Publication Date

11-24-1964

Abstract

The objective of this study was to gain additional insight into the phenomenon of spin-orbit coupling in molecules by examining the intramolecular mechanisms responsible for the phosphorescence of certain types of molecules. Spectrocopic investigations of a series of aromatic hydrocarbons, aromatic heterocyclics, and some of their halogen derivatives are reported. Experimental measurements included absorption spectra, total emission spectra, polarized emission spectra, obtained by the method of photoselection, and radiative lifetimes. It was found that chlorine substitution in naphthalene, quinoline, and quinoxaline has the effect of enhancing the transition probability for radiative transitions from the Blu component of the 3B3u+ lowest triplet state of the chloroderivatives of these compounds. It is shown theoretically that the only possible direct spin-orbit coupling schemes which are in agreement with the polarization data involve the Blu component of the lowest triplet state interacting with Blu states in the singlet manifold, or the ground state interacting with Ag components of the triplet manifold. Since the lowest singlet in naphthalene has Blu symmetry and is only 10,000cm-1 removed from the 3B3u lowest triplet state, compared to a calculated 25,000cm-1 separation between the ground state and the nearest 3Ag state, it is considered likely that the primary coupling scheme is 1B1u ---- 3B3u (Blu). Bromine substitution in naphthalene, quinoline, and quinoxaline seems to have the additional effect of introducing strong vibronic coupling involving a non-totally symmetric vibrational mode, and producing mixed polarization in the polarized spectra. The phosphorescence as well as the fluorescence of cinnoline and its derivatives apparently originates from an ո-π* state, rather than from a π-π* state, as in other two-ring compounds. The assignment of the lowest triplet as an ո-π* state is based on the fact that its energy is several thousand reciprocal centimeters lower than any analogous π-π* triplets, paralleling the shift of the ո-π* singlet state; and that the 1400cm-1 vibrational frequency found in all π-π* phosphorescence, is missing. An example of emission which appears to originate from an excitation dimer has been observed in 1, 4-diazaanthracene. What appears to be a similar type of emission in 9-chloro­acridine and 9, 10-diazaanthracene is believed to originate from the photoreduction products of these compounds. Similarities in the polarized spectra of naphthalene, quinoline, and quinoxaline lead to the proposal of an explanation of the origin of the phosphorescence of naphthalene, based on the breakdown of the π electron approximation.

Project Sponsors

The National Aeronautics and Space Administration

Language

English

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Glenn Arthur Crosby

Second Committee Member

Raymond N. Castle

Third Committee Member

Milton Kahn

Fourth Committee Member

Roy Dudley Caton Jr.

Fifth Committee Member

Masanobu Yamauchi

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