Quenching mechanism of the UO22+ excited state by phenols and related compounds in aqueous solutions

Quenching rate constants, k(q), of the uranyl excited state by phenolic com pounds were determined in H3PO4 1M by luminiscence techniques. A plot of lo g k(q) vs. Delta G(2) for the photo-induced electron transfer reaction rend ered a slope value of 4.0 eV(-1) which was much smaller than that predicted from the Rehm-Weller correlation (16.9 eV(-1)). This value is similar to t hose found for aromatic quenchers that fail to interact with the UO22+ grou nd state, and quench the uranyl luminescence through a non-radiative donor- acceptor complex formation.