Transient Photoresponse of the Tris(2,2‘-bipyridine)ruthenium(II)-Catalyzed Minimal Bromate Oscillator

Abstract

The tris(2,2‘-bipyridine)ruthenium(II)-catalyzed minimal bromate oscillator under flow conditions was found to exhibit various dynamical responses to the pulsed-light perturbation in the visible region. The system in its reduced steady state exhibits excitability with a threshold in the applied light-pulse energy, while the oxidized steady state does not respond to the light pulse. The latter exhibits, however, a slow response without a threshold to the negative light pulse. The system in its oscillatory state exhibits a phase shift of oscillations upon application of a pulsed-light perturbation. The oscillation phase is mostly advanced or unaffected, depending on the phase of application of the light pulse, although a narrow region of phase delay has also been found in between. A phase portrait spanned by the redox potential and the bromide ion-selective electrode potential has been determined experimentally on the basis of which the system dynamics is discussed in detail. All these results suggest the importance of the photoproduction of extra HBrO2 upon pulsed-light illumination to induce the autocatalytic process that forces the system to experience a single turn along the limit cycle. A numerical calculation based on the Noyes−Field−Thompson model has supported the proposed features, demonstrating that the pulsed addition of HBrO2 reduces the concentration of Br- quickly. When it is reduced below a certain threshold value, the autocatalytic growth of HBrO2, as well as of the catalyst in its oxidized form, is initiated to exhibit the response corresponding to the observation.