Preface

When you are in total darkness, the appearance of even a faint light conjures feelings of security and hope. Everyone has experienced this magical sensation at some point of their life when, for example, a candle is lit at night. It is a primal feeling, probably related to the instinct for survival. We are drawn to the light, take comfort in it and associate it with a sense of wonder and beauty. This book is filled with stories about beautiful reactions and experiments that produce light in the dark. Usually in electrochemistry, we measure potentials and currents and largely draw our conclusions from these abstract variables. But there is a special kind of electrochemistry where the final product of the reaction is light. It is called electrogenerated chemiluminescence and the materials and methods associated with it are now sufficiently well understood that everybody can experience it in their own laboratory. But be warned, the beauty of this phenomenon may cause you to be drawn into this intriguing research field like a moth to a flame. This was the case for some of the contributors of this book. In addition, it may remind you of a similar feeling that you had as a child running up a hill and trying to catch a firefly in your hands, watching its regular light emission and letting it fly again.

Electrogenerated chemiluminescence, also called electrochemiluminescence (ECL), is the generation of light triggered by an initial electrochemical reaction. Electron-transfer is at the core of the ECL phenomenon since it occurs at the electrode surface to initiate the process and also later to generate the excited state of the luminophore. The modern history of ECL started in the mid-1960s with the electrochemical investigation of radical ions of aromatic hydrocarbons in organic solvents. Studying the highly exergonic recombination reactions of these radical ions helped us to understand some of the most fundamental questions relating to electron-transfer and opened a new era for ECL. Over the last five decades, the topic underwent a continuous transformation from studying mostly fundamental aspects without apparent practical applications to the development of powerful and ultrasensitive analytical methods, which have been successfully commercialized in the healthcare diagnostic market for the detection of biomarkers in body fluids. Indeed, if you consider the terms ‘electrochemistry of aromatic hydrocarbons in organic solvents’, it does not suggest a priori a fashionable research area with societal impact, as it is often required nowadays by the funding agencies. On the one hand, it is a perfect example of how difficult it is to evaluate a grant proposal and to envision the outcomes of the fundamental research with a short-term view using a simple linear extrapolation from current knowledge. On the other hand, it illustrates the importance of supporting the fundamental aspects of research.

Complexity and beauty from both electrochemistry and photophysics crystallize in the ECL process. Indeed, this light-emission phenomenon intimately combines the orthogonal modalities of electrochemical stimulation and optical detection. Due to its interdisciplinary nature and also to its remarkable intrinsic properties, ECL attracts growing interests in diverse scientific fields. In addition, ECL is an ideal area for students to gain multidisciplinary scientific training because they will learn techniques, methods, concepts, tools in electrochemistry, photophysics, photochemistry, simulation, analytical chemistry, bioassays, etc. The duality of ECL where we wish to master the electron and the photon opens exciting possibilities and implies also that the toolbox must be very diverse.

Looking at the past and present of ECL, it is clear that it is a research field that continues to expand rapidly towards new horizons by exploiting all facets of electrochemistry and spectroscopy such as nanoelectrodes, bipolar electrochemistry, polarization, microscopy, photonics, plasmonics, etc. The aim of this book is to provide a modern global view of ECL, which is accessible to students and researchers in the physical, chemical, materials and biological sciences. This work covers the fundamental aspects of ECL as well as its analytical and imaging applications. I wish to thank all of my co-authors for their enthusiasm and contributions. I hope that the readers will find this book useful and instructive whilst motivating them to explore this fascinating and important interdisciplinary field further.

Neso Sojic