Part I. Radiationless Transitions in Organic Systems: Determination of Intersystem Crossing Yields in Fluid Solution. Part II. Intramolecular Energy Transfer Between Non-Conjugated Chromophores in Some Model Compounds

Citation

Lamola, Angelo Anthony (1965) Part I. Radiationless Transitions in Organic Systems: Determination of Intersystem Crossing Yields in Fluid Solution. Part II. Intramolecular Energy Transfer Between Non-Conjugated Chromophores in Some Model Compounds. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/b837-bk69. https://resolver.caltech.edu/CaltechETD:etd-09262002-115009

Abstract

PART I

The efficiency of reaching the lowest triplet state after excitation into low excited singlet levels was determined for benzene, naphthalene, and other polycyclic aromatic hydrocarbons as well as for a number of carbonyl compounds and amines in fluid solution at room temperature. The determinations were accomplished by a chemical method in which the compound in question is used as a photosensitizer for the cis-trans isomerization of suitable olefins. Conditions are such that olefin molecules quench all triplet sensitizer molecules; the olefins subsequently undergo geometric (cis⇌trans) isomerization. The details of the isomerization reaction are known and a simple determination of the quantum yield for the sensitized isomerization leads directly to the quantum yield of sensitizer triplets.

From the data, intersystem crossing rates are estimated, as well as efficiencies and rates of radiationless triplet-to-ground-state transitions. Some information concerning the mode and importance of radiationless first-excited-state-to-ground-state transitions is also included, as well as a discussion of the results in terms of present theoretical treatments of radiationless transitions.

PART II

Intramolecular transfer of both singlet and triplet electronic excitation in the Leermakers' Compounds, 4-(1-naphthylmethyl) -benzophenone (LI), 1-(1-naphthyl)-2-(4-benzoylphenyl)ethane (LII), and 1-(1-naphthyl)-3-(4benzoylphenyl)propane (LIII) occurs and has been studied in some detail. In addition to emission spectroscopy, chemical methods for detecting, characterizing, and counting molecules in triplet states were employed.

In all three compounds, totally efficient transfer of triplet excitation from the benzophenone groups to the naphthalene moieties occurs, and at nearly the same fast rate (k > 10¹⁰ sec⁻¹).

Transfer of singlet excitation from the naphthalene moiety to the benzophenone group is about 90% efficient in LI, 75% efficient in LII, and 85% efficient in LIII. The rate of the singlet energy transfer (k ~ 10⁷ - 10⁸ sec⁻¹) are much slower than the rate of the triplet excitation transfer. The fluorescent emissions from the Leermakers' Compounds exhibit a quite different spectrum than that from 1-methylnaphthalene, and significant bathochromic and hyperchromic effects are noted in the absorption spectra of the compounds. The nature of singlet excitation transfer in the Leermakers' Compounds is quite complex, and large stereochemical effects no doubt exist. A discussion of the results in terms of the several presently accepted mechanisms for electronic energy transfer is included

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