A TIME-RESOLVED DIFFUSE-REFLECTANCE STUDY OF THE PHOTO-REDUCTION OF 2,2'-BIPYRIDINE IN FAUJASITIC ZEOLITES

The siting location and conformation of 2,2'-bipyridine sorbed alone a nd co-sorbed with 1,4-diazabicyclo(2.2.2)octane (DABCO) in several fau jasitic zeolites with different aluminium content were determined by a Raman spectroscopic study and Monte Carlo simulations. Theoretical an d experimental results clearly indicate a trans --> cis conformational change of the 2,2'-bpy molecule upon sorption into dehydrated Na(n)FA U (ii = 56, 85) whereas the trans conformation is retained in the pure ly siliceous zeolite FAU (n = 0). The UV photolysis of 2,2'-bpy molecu les sorbed alone generates a triplet excited state via singlet states, whereas in the case of co-sorbed DABCO, the photo-reduction of 2,2'-b py by the amine leads to the radical anion. (C) 1997 Elsevier Science B.V.