Photochemistry and Photophysics

Concepts, Research, Applications

Vincenzo Balzani, Paola Ceroni, Alberto Juris

• Publisher: Wiley-VCH
• Year: 2014
• ISBN:
  9783527671045
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

This textbook covers the spectrum from basic concepts of photochemistry and photophysics to selected examples of current applications and research.
Clearly structured, the first part of the text discusses the formation, properties and reactivity of excited states of inorganic and organic molecules and supramolecular species, as well as experimental techniques. The second part focuses on the photochemical and photophysical processes in nature and artificial systems, using a wealth of examples taken from applications in nature, industry and current research fields, ranging from natural photosynthesis, to photomedicine, polymerizations, photoprotection of materials, holography, luminescence sensors, energy conversion, and storage and sustainability issues.
Written by an excellent author team combining scientific experience with didactical writing skills, this is the definitive answer to the needs of students, lecturers and researchers alike going into this interdisciplinary and fast growing field.

1
Introduction

1.1 Photochemistry and Photophysics in Science and Technology

Photochemical and photophysical processes have been intimately related to the development of man and his environment even before his appearance on the planet. Ever since the first morning of Creation, life has not been merely a chemical process but one in which light from the Sun played a significant role: thus, photochemistry. In the first instance, simple photochemical reactions caused by the Sun's rays generated organic molecules from the constituents of the primitive atmosphere on the Earth. Subsequently, a sophisticated series of photochemical and photophysical processes, now referred to as photosynthesis, made it possible for simple cells to become autotrophic, provided the necessities of life, stored solar energy in the form of fossil fuels, and still supply us with practically all our food.

From the point of view of living matter, however, photochemistry is more than the means of using the energy of light. It is also a means of sensing the environment (vision), an indicator of the time of day and the season, a source of damage to cellular constituents, and a mechanism for repairing some cellular damages. Photochemistry is also heavily involved in processes that determine the composition of matter in the interstellar space, and in the formation of atmospheric pollutants. Of course, photophysical processes also occur in nature. Suffice it to say that the world would not be colored if sunlight were completely absorbed or completely reflected by the objects that surround us, and we would not be able to enjoy fireflies or other beautiful scenes without bioluminescence.

Each of these natural processes provides a sufficient reason for a scientific interest in photochemistry and photophysics. However, photochemistry and photophysics are also important from an artificial viewpoint. Their impact in the chemical, physical, biological, and medical sciences and technologies, including nanotechnology, is being felt increasing in a spectacular manner. Photochemical methods are used for producing polymeric printing plates and printed circuits, for UV (ultraviolet) curing of surface coatings and printing inks, and for laboratory and commercial synthesis of high-value chemical compounds. Photochemical and photophysical concepts are at the basis of important applications such as protection of dyes and plastics (and also human skin) from the damaging effect of sunlight, waste water cleaning, design of fluorescent compounds for a variety of sensing applications (wind galleries, security, optical brighteners, pollutant detectors, display devices, molecular switches and logic gates, biological markers, cellular properties, and functions), creation of photochromic materials used in sunglasses, fashion clothes and optical memories, and development of laser devices and of light-powered molecular machines. Other interesting fields concern photomedicine, multiphotonic processes, solar-powered green synthesis, molecular photovoltaics, and solar energy conversion by water photodissociation. These and other topics are dealt with in the subsequent chapters of this book.

1.2 Historical Notes

Artificial photochemical reactions have been observed as long as chemistry has been studied. Most of the earlier observations, however, were accidental and remained unexplained. The first investigation was made in 1777 by the Swedish chemist Carl W. Scheele, who observed that violet light was the most effective in darkening silver chloride. But it was only in 1817 that Theodor von Grotthuss established that only the light absorbed is effective in producing photochemical change. This first general principle of photochemistry passed unnoticed until 1841, when it was restated by John W. Draper and, as a consequence, is now termed the Grotthuss–Draper law.

Photochemistry emerged from its empirical stage when modern physics established that light is radiated in discrete quanta, called photons, with an energy proportional to the frequency of the light, and that absorption corresponds to the capture of a photon by an atom or a molecule. With this concept in mind, Johannes Stark and Albert Einst...