Preface

*Recent Advances in Chemical Kinetics* provides insight into different aspects of chemical reactions. Over six chapters it covers both basic and advanced topics, including solvent catalysis, customized flow reactors, p-conjugation in kinetics, kinetics of autoxidation, molecular chameleon for cations and anions, and internal clocks of atoms.

Chapter 1, "Solvent Catalysis in the Sensitizer-Mediator Redox Kinetics", describes the effect of solvents as an important aspect of the sensitizer-mediator interaction in the reaction medium. It discusses The catalytic role of a small-volume fraction of organic solvent in the aqueous electron transfer kinetics of a few putative sensitizermediator reactions is discussed in this chapter. It also investigates the reduction of dicyanobis(2,2'-dipyridyl)iron(III) and dicyanobis(1,10-phenanthroline)iron(III) in binary solvent media, including dilute tertiary butyl alcohol (TBA)-water and dilute 1,4-dioxane-water, the reduction of dicyanobis(2,2'-dipyridyl)iron(III) and dicyanobis(1,10-phenanthroline)iron(III) was investigated.

Chapter 2, "Process Intensification in the Customized Flow Reactors", discusses the design, development, and characterization of continuous flow reactors through RTD studies. It also provides an overview of dimensionless numbers and their influence on the flow reactors, effect of kinetic parameters on batch and flow systems, estimation of various thermodynamic properties to assist equipment design, process intensification of continuous flow reactors to achieve maximum performance, validation of reactors using well-known reaction system and listing out advantages of flow reactors over batch processes.

Chapter 3: "Catalytic Behavior of Extended π-Conjugation in the Kinetics of Sensitizer-Mediator Interaction", discusses the catalytic effect of extended π-conjugation on the electron transfer process between ferricyphen-ferrocyanide and ferricypyr-ferrocyanide in an aqueous medium. Ferricyphen and ferricypyr may be feasible options for the sensitizer in dye-sensitized solar cells due to their high reduction potential, stability, capability as an outer-sphere oxidant, and photosensitivity. This chapter compared the ability of competent putative sensitizers to oxidize the likely mediator in water.

Chapter 4: "The Kinetics of Autoxidation in Wine", explains how tartaric acid can be oxidized in the presence of iron without peroxide in the air. This chapter explores the theoretical considerations of iron complexes formation, oxygen activation, an autoxidative mechanism, and experimental measurements of tartaric acid oxidation as the basis of autoxidation in wine. It discusses the role of iron complexes in the activation of oxygen, the formation of reactive oxygen species, and the initiation of autoxidation, which are crucial for understanding wine oxidation kinetics. Mechanisms based on hydroxyl radicals versus the ferryl species are likely to have different oxidation products of wine components based on pH effects.

Chapter 5: "The ESIPT-Steered Molecular Chameleon for Cations and Anions Based on Alizarin and Alizarin-S: A Comparative Study", deals with the chemosensing properties of Alizarin (A3) and Alizarin S (AS3) toward anions and cations in acetonitrile (CH3CN). The absorption and fluorescence properties of the two molecular entities were investigated in CH3CN. Based on the excited state intermolecular proton transfer system (ESIPT), the probes were able to collectively discriminate specific cations (Cu2+, Zn2+, Ni2+, Fe3+, Fe2+) and anions (F− , CN− , OH− , AcO− and N3 − ) via colorimetric observations and spectrometric activities. The simultaneous fluorescence effects were ascribed to the deprotonation activities experienced by A3, as excess anion quantities were added. The sulfonyl electron withdrawing group had an effect in the Alizarin structure, towards the discrimination of anions and cations, both colorimetrically and fluorometrically.

Chapter 6: "Perspective Chapter: Slowing Down the "Internal Clocks" of Atoms – A Novel Way to Increase Time Resolution in Time-Resolved Experiments through Relativistic Time Dilation", discusses how to achieve 2–3 orders of magnitude higher time resolutions than is possible with laser and electron compression technology. The proposed novel method is designed to slow down the "internal clock" of the sample.

I would like to thank the staff at IntechOpen for their cooperation throughout the process of publishing this book.

> **Dr. Muhammad Akhyar Farrukh** Professor, Faculty of Science and Technology, Department of Basic and Applied Chemistry, University of Central Punjab, Lahore, Pakistan

> > **1**

**Chapter 1**

**Abstract**

**1. Introduction**

*Rozina Khattak*

Solvent Catalysis in the

Sensitizer-Mediator Redox Kinetics

The sensitizer-mediator redox reaction is a vital component of the dye-sensitized solar cells (DSSCs). The efficiency and stability of dye-sensitized solar cells are aided by the kinetics of this redox process. Several reaction parameters influence the kinetics of a reaction, and if those parameters are controlled, the rate of the process and its results can be controlled. One of the most important aspects of the sensitizer-mediator interaction is the reaction medium. Aqueous DSSCs are unquestionably a good replacement when it comes to taking a green approach to avoiding toxic, flammable, and volatile organic solvents and their mixtures, which are commonly used in DSSCs and are known to harm the environment while also reducing the lifetime and stability of the DSSCs. The catalytic role of a small volume fraction of organic solvent in the aqueous electron transfer kinetics of a few putative sensitizer-mediator reactions is discussed in this chapter. In binary solvent media including dilute tertiary butyl alcohol (TBA)-water and dilute 1,4-dioxane-water, the reduction of dicyanobis(2,2′ dipyridyl)iron(III) and dicyanobis(1,10-phenanthroline)iron(III) was investigated. The reactions were carried out in a 10% TBA or dioxane to water media with a volume-volume fraction of both solvents using iodide as a reducing agent. The effect

of several parameters on the rate constant was also calculated and analyzed.

**Keywords:** dye-sensitized solar cells, solvents, kinetics, redox reaction, catalysis

In the kinetics of reactions, particularly redox reactions, the solvent has a significant effect. Redox reactions occur when two responding entities exchange electrons. The electron giver, or reducing agent, is the one who contributes the electron; the electron acceptor, or oxidizing agent, is the one who accepts the electron. The donation and reception of electrons alter the oxidation states of the reactants since electrons are such small charged particles. As a result, the solvent plays an important role in electron transfer reactions. A few of the most influential characteristics that govern redox reactions include solvation, viscosity, and hydrogen bonding [1]. The solvent organizes and reorganizes itself around the reactants and products before and after the electron transfer event. Similarly, the solvent organizes and reorganizes around the reactants during the production of the transition state [2]. According to the transition state theory of reactions in solution and the double sphere model, the rate constant is related to the dielectric constant of a medium using the following expression [3].
