PHOTOCHEMISTRY OF 4,4'-BIPYRIDINE - NANOSECOND ABSORPTION AND RAMAN-STUDY OF THE HYDROGEN-ATOM ABSTRACTION FROM METHANOL AND 2-PROPANOL

The transients that are produced in the photolysis of 4,4'-bipyridine (44BPY) in methanol and in 2-propanol have been examined by use of tra nsient absorption and time-resolved resonance Raman spectroscopies in the nanosecond time range. 4,4'-Bipyridine undergoes photoreduction by these alcohols, leading to the hydrogen adduct radical 44BPYH.. The r eaction arises via quenching of the T1 state of 44BPY by the abstracti on by a nitrogen atom of a hydrogen atom from methanol (k(Q) = 1.05 X 10(5) M-1 s-1) or 2-propanol (k(Q) = 2.4 x 10(5) M-1 s-1). The 44BPYH. radical decays via disproportionation in competition with protonation by the solvent. In methanol, an additional very fast reaction of form ation of the 44BPYH. radical is observed besides the above hydrogen tr ansfer to the T1 state. It is suggested that this fast reaction result s from the double transfer of an electron and a proton in the excited S1 state of H-bonded bipyridine or bipyridine aggregates.