Kinetic Studies of Energy Transfer to the Geometric Isomers of Stilbene and 1,2-Diphenylpropene by Kinetic Spectrophotometry

Author: Herkstroeter, William George

Year: 1966

Degree: Dissertation (Ph.D.)

Advisor: Hammond, George Simms

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/5q92-f570

Abstract

The rate constants for triplet energy transfer from a series of photosensitizers to the cis and trans isomers of stilbene and 1,2-diphenylpropene in benzene solution at room temperature have been measured by kinetic spectrophotometry. A plot of rate constants vs. triplet excitation energies of the sensitizers shows that there is a smooth transition from diffusion controlled to immeasurably small rates. Even when the triplet of the sensitizer is appreciably less energetic than the spectroscopic triplet of the acceptor, energy transfer takes place. In accord with previous work in these laboratories, this observation is interpreted in terms of non-vertical excitation in which the acceptor is excited to a triplet having lower energy and different geometry than the spectroscopic triplet. By contrast, dibenzcycloheptenol, selected as an isoenergetic and rigid model for cis-stilbene, accepts triplet energy less efficiently than cis-stilbene from a sensitizer having less than the spectroscopic triplet energy of these molecules. Evidence that 2, 4, 6-triisopropyl-4'-methoxybenzophenone transfers triplet energy to cis- and trans-stilbene at a reduced rate because of steric hindrance indicates that factors other than the relative triplet energies of sensitizer and acceptor can be important in the process of energy transfer.

Files