**4. Conclusion**

The kinetic study of the electron-transfer reaction between ferricyphenferrocyanide and ferricypyr-ferrocyanide revealed a complex mechanism. The reactions were completed into two phases. The initial phase of the reactions lasted long enough to complete the reaction at 70% efficiency and was independent of the sensitizer-mediator concentrations. This phase kinetics has been the most straightforward, with zero order corresponding to the sensitizer and mediator in the aqueous medium. The second phase of the reactions, on the other hand, was long enough to

account for up to 30% of the total reaction time, with a first-order relationship of the rate of redox reactions on the concentration of sensitizers and mediator. In the second phase, the reactions followed an overall second order. The rate, that is second order rate constant, of the reaction was shown to be dependent on pH and the concentration terms involved, indicating that it was a rate-determining step involving interaction between ferricyphen or ferricypyr and ferrocyanide. However, as free ferrocyanide is consumed to generate monoprotonated ferrocyanide with increasing acidity, the rate of reaction in this phase slows down, indicating that this is the slow stage of the process. As a result, it has been discovered that monoprotonated ferrocyanide reduces sensitizer in the first phase of the reaction, which is a fast kinetic step in the electron transfer process. Meanwhile, the findings demonstrated that pi-conjugation in the sensitizer has a catalytic influence on the redox kinetics of the sensitizer-mediator interaction. When compared to less conjugated sensitizer that is ferricypyr, piconjugation increases the coordination compound's or sensitizer's (ferricyphen's) electron affinity, allowing it to receive electrons and oxidize the mediator more quickly.
