Photochromic transformations in solutions of 8,8′-diquinolyl disulfide and di(mercaptoquinolinato)nickel(II)

Abstract

The nature of intermediate species and their reactions were studied by laser pulse photolysis for a photochromic system consisting of 8,8´ diquinolyl disulfide (RSSR) and a planar Ni II complex di(mercaptoquinolinato)nickel(II) (Ni(SR) 2 ) in toluene and benzene solutions. Un der exposure to laser radiation, disulfide RSSR dissociates to two RS • radicals, whose spectrum has an intense absorption band with a maximum at λ = 400 nm (ε = 8400 L mol -1 cm -1 ). The radicals disappear by recombination (2k rec = 4.6•10 9 L mol -1 s -1 ). In the presence of the Ni(SR) 2 complex, coordination of the radical (k coord = 4.4•10 9 L mol -1 s -1 ) competes with recombination to form a radical complex RS • Ni(SR) 2 having an intense absorption band with a maximum at 460 nm (ε = 16 600 L mol -1 cm -1 ). This species decays in the second order reaction (2k = 4.6•10 4 L mol -1 s -1 ). Since the photochromic system returns to the initial state, the reaction of two radical complexes is assumed to produce radical recombination and reduc tion of the disulfide and Ni(SR) 2 complex. Analysis of the kinetic data showed that some RS • radicals decay in the microsecond time interval due to the reaction with the RS • Ni(SR) 2 radical complex (k = 3.1•10 9 L mol -1 s -1 ).