Chemical clock reactions with organic dyes: Perspective, progress, and applications

A chemical clock reaction is a process where a periodic change in color is observed with the progress of a reaction. Nonlinear kinetic clock reactions are associated with a visible color change caused by redox phenomena or a change in the concentration of certain dye components. The redox activities of dyes are dependent on the reaction conditions and catalyst used. This review is based on the clock reaction using organic dyes. The choice of dye was based on the properties, such as water solubility. The dyes must show distinct and different visible color variations in the oxidation and reduction state of dyes. The various dyes were tested for the following: (1) color variation; (2) redox behavior of different dyes in various catalytic systems; (3) rate determination of clock reactions with the alteration of dyes; (4) study of the interaction of dyes with the catalyst and reaction medium. Water-soluble organic dyes can be applied as a redox indicator, where the redox behavior of dyes and the nature of catalysts are responsible for the alteration of formal oxidation and reduction potential values. Catalytic modifications were carried out to control the rate of the clock reaction to identify the redox kinetics in a free solution or organized media, such as micelles and reverse micelles. The use of nanocatalysts broadened the use and application range of the clock reaction. A wide range of pH can be used to control the redox activity of dyes and the rate of the clock reaction that might significantly improve the clock cycles. The visual detection of oxidation-reduction is simple to monitor using common instruments, such as UV–vis spectroscopy. Clear and concise documents for the clock reaction from classical blue bottle experiments and their development with various catalytic systems and modern and rapid versions are also included. A brief plausible mechanism for synthesizing catalytic systems and their effect on clock reactions are discussed. The difference in the clock reactions with adsorption and degradation are also described. The importance of the clock reactions in various fields is also documented.