TIME-RESOLVED ESR EXAMINATION OF A SIMPLE SUPRAMOLECULAR GUEST-HOST SYSTEM - ELECTRON-SPIN EXCHANGE INTERACTION IN MICELLIZED SPIN-CORRELATED RADICAL PAIRS

The electron spin exchange interaction between micellized spin-correla ted radical pairs (SCRP) is investigated by time-resolved electron spi n resonance (TRESR) spectroscopy. On the basis of the SCRP model propo sed independently by Closs and McLauchlan, an effective exchange inter action (J(eff)) can be extracted either from a direct reading of the o bserved TRESR spectra or through spectral simulation. The results for a series of micellized radical pairs (of similar electronic and magnet ic structure) show that the J values are a function of the effective m icelle size (L(eff)) experienced by a given micellized radical pair an d also a function of the radical pair molecular structure for a given micelle size. The values of J(eff) can be systematically manipulated b y varying the size of the micelles and/or the structure of the radical pairs. The results are shown to be consistent with a simple model of the structure of the micelle which includes the relationship between t he magnitude of the exchange interaction between the fragments of the micellized radical pair and the micellar parameters such as the freque ncy of geminate pair reencounters, the relative diffusion coefficient of the fragments in the micelles, and the effective volume of the mice lle explored by the pair during the time of observation. It is shown t hat a micellized radical pair, because of interactive spin and molecul ar dynamics, constitutes a simple and useful model of a guest-host sup ramolecular structure so that variations of the micelle size and the r adical pair structure are interacting and not independent variables.