Investigation of the Triplet State Properties of Bis(chlorophyll)cyclophane and Its Partially Metalated Derivatives
Litteken, Susan Roberta
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https://hdl.handle.net/2142/70224
Description
Title
Investigation of the Triplet State Properties of Bis(chlorophyll)cyclophane and Its Partially Metalated Derivatives
Author(s)
Litteken, Susan Roberta
Issue Date
1983
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
Bis(chlorophyll)cyclophane was originally synthesized as a model system for the light to energy conversion in green plant photosynthesis. The molecule is two synthetically linked chlorophyll macrocycles stacked center to center with the Q(,y) transition dipoles of each macrocycle perpendicular. Zero, one, or two magnesium(II) ions can be inserted into the macrocycles. The properties of the photoexcited triplet state of the cyclophanes were studied using light modulated EPR (electron paramagnetic resonance) techniques on frozen solutions at 9K.
Monomagnesiated cyclophane proved to be the most interesting of the cyclophanes. In solvent systems where the magnesium was pentacoordinate, the EPR spectrum of monometalated cyclophane contained two superimposed triplets. One triplet was attributed to the metalated macrocycle and the other triplet was attributed to the nonmetalated macrocycle. Whereas when the magnesium was hexacoordinate, the EPR spectrum of monometalated cyclophane contained only one triplet attributed to the metalated macrocycle. When the nonmetalated macrocycle of hexacoordinate monometalated cyclophane was selectively excited, the EPR spectrum still contained only a triplet from the metalated macrocycle. Thus, it was concluded that an energy transfer takes place in hexacoordinate monometalated cyclophane from the nonmetalated macrocycle to the metalated macrocycle. No evidence of energy transfer was found in the other cyclophanes.
Information about some of the triplet state properties can be obtained by comparing the EPR spectra of all the cyclophane compounds. Relative population and depopulation rates of the triplet sublevels were obtained from the spin polarization pattern of the spectra. Also an idea of the behavior of the triplet across the molecule can be obtained by comparing the values of the zero fields splitting parameters of the cyclophanes with those of monomeric compounds.
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