CHARGE-TRANSFER EXCITATION OF ELECTRON DONOR-ACCEPTOR COMPLEXES IN ZEOLITE MATRICES - DIRECT OBSERVATION OF RADICAL-ION PAIRS FROM PICOSECONDS TO MILLISECONDS BY DIFFUSE-REFLECTANCE LASER FLASH-PHOTOLYSIS

Laser excitation of charge-transfer complexes between pyridinium-analogous accepters and arene donors incorporated into zeolite-Y and zeolite-L generates transient radical ion pairs that can be monitored using time-resolved diffuse-reflectance spectroscopy techniques. At least three types of radical ion pairs have been distinguished kinetically with lifetimes from picoseconds to milliseconds, depending on donor and acceptor strength and on the zeolite type. As cause for the complex decay kinetics, the interactions between the radical ion pairs and the zeolite framework leading to spatial separation are discussed. Furthermore, the unique effects of coadsorbed water are described.