The Photophysics of Azulene and Related Compounds in Solution
Date
1995
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Degree Level
Doctoral
Abstract
Owing to their unusual spectroscopic properties, azulene and other nonalternant, aromatic molecules have been the focus of much research over the past four decades. Despite these efforts, the factors controlling the excited
state decay of such molecules remain unclear, and a comprehensive description of their photophysical properties has not emerged. The research presented in this thesis was undertaken to provide a systematic study of the excited state dynamics of azulene and related compounds in fluid media.
Time-correlated, single-photon counting was used to obtain the excited state decay rates of the S2 states of azulene and five of its derivatives. A pump-probe spectrometer with sub-picosecond temporal resolution was employed to obtain the very short population relaxation times of the nonemitting S1 states of azulene and related compounds as a function of the solvent polarity, the solvent viscosity, chemical substitution of the chromophore, and the excitation wavelength. The pump-probe method, in combination with polarization rotation, was also used to obtain information about the excitation mechanism of the laser dye a-NPO.
The electronic relaxation rates of the S2 states of azulene and its simply-substituted derivatives are individually correlated with their S2-S1 energy gaps, while the S1 relaxation rates of azulene and all of its derivatives exhibit a single, energy gap law correlation with the S1-S0 energy spacings in solvents of different polarity and viscosity. The lifetime of one azulene derivative with a sub-picosecond decay time depends on the excitation wavelength. The radiationless decay rates of the S1 states of four pseudoazulene derivatives are also consistent with an S1-S0 energy gap law correlation.
The excitation mechanism of cc-NPO is dominated by the absorption of two or four photons depending on the intensity of the exciting light. Perturbation theory can be used to accurately model the laser-molecule interactions and to predict the excitation mechanism. By combining theory and experiment, several molecular parameters of a-NPO can be obtained.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry