Chemistry of High-Energy Content Reagents

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The photochemical, photophysical, and spectroscopic properties of ion pairs formed from cationic dyes and anionic borates will be studied. The first question to be considered will be whether or not the boranyl radicals formed by one electron oxidation of borates are bound species. This will be addressed by application of time-resolved spectroscopic methods on picosecond and femtosecond time-scales. Since the lifetime of boranyl radicals is too short to permit measurement of the oxidation potential by electrochemical means, a kinetic method based on the Rehm-Weller equation will be applied to estimate their potentials. A series of borates will be prepared to investigate the effect of steric crowding in the borate upon the oxidation potential. Penetrated ion pairs will be prepared that have different encounter distances, orientation, and free energy changes for photoinitiated electron transfer reactions. With these various penetrated ion pairs, factors that control forward and back electron transfer will be analyzed. This grant from the Organic Dynamics Program supports the continuing work of Professor Gary B. Schuster at the University of Illinois. Ion pairs will be formed from positively charged dyes and negatively charged borates. The borates contain a total of four other carbon containing groups ( alkyl or aryl groups) bonded to the boron atom. These ion pairs will be irradiated with light which is absorb by the dye. An electron will be transfer from the dye to the borate, which will in turn cause an alkyl group to dissociate from boron in the form of a free radical (a carbon species with one unpaired electron). The efficiency of this reaction, which depends in part on the back-transfer of an electron to give the starting ion pair, will be studied as a function of the structure of the ion pair. These ion pairs have practical importance, since they can initiate polymerization upon irradiation with visible and infrared light. The wide co mmercial application of polymers makes these ion pairs of commercial interest.