Photochemistry

Photochemistry
Masohe · CC BY-SA 4.0 · source
Name	Photochemistry
Field	Chemistry, Physical chemistry, Physics
Notable practitioners	Albert Einstein, Gerty Cori, Gerhard Herzberg, Ahmed Zewail, Niels Bohr, Robert Mulliken, Linus Pauling

Photochemistry Photochemistry examines chemical transformations induced by electromagnetic radiation, especially visible and ultraviolet light. It connects experimental methods, theoretical models, and technological implementations developed across institutions such as the Max Planck Society, Massachusetts Institute of Technology, and Royal Society laboratories. Work in the field has been recognized by awards including the Nobel Prize in Chemistry and has influenced projects at organizations such as Bell Labs, Lawrence Berkeley National Laboratory, and NASA.

Introduction

Photochemistry arose from early studies by investigators at establishments like the Royal Institution and the French Academy of Sciences, where researchers correlated light with chemical change. Seminal contributors include John Herschel and Humphry Davy in observational experiments and theoreticians from the University of Göttingen and Harvard University who framed foundational concepts. The discipline bridges laboratories at universities such as University of Cambridge and industrial research centers like DuPont and General Electric, driving advances in spectroscopy, catalysis, and materials.

Fundamental Principles

Photochemical processes are governed by quantum transitions between electronic states described by models from Niels Bohr and developed by theorists at the Institute for Advanced Study and Columbia University. Absorption follows selection rules connected to molecular symmetry analyzed using group theory from École Normale Supérieure mathematics programs and computational methods from groups at Stanford University. Key concepts include electronic excitation, intersystem crossing, internal conversion, and photophysical relaxation pathways explored by scientists at ETH Zurich and University of California, Berkeley. Energy transfer mechanisms such as Förster resonance energy transfer trace to work influenced by researchers affiliated with Max Planck Institute for Biophysical Chemistry and Rockefeller University. Quantum yields, actinometry, and Franck–Condon principles link to spectroscopy techniques developed at institutions like Imperial College London.

Experimental Techniques and Instrumentation

Experimental photochemistry employs lasers from manufacturers and labs connected to Lawrence Livermore National Laboratory and Rutherford Appleton Laboratory for time-resolved experiments. Ultrafast spectroscopy using femtosecond pulses pioneered by groups at California Institute of Technology and University of Glasgow enables pump–probe studies; transient absorption, fluorescence upconversion, and time-correlated single-photon counting are implemented in centers such as Argonne National Laboratory. Steady-state photolysis chambers and actinometers used in laboratories at Scripps Research and Johns Hopkins University quantify photon flux and quantum efficiency. Instrumentation also integrates cryostats from companies collaborating with CERN and monochromators designed with input from National Institute of Standards and Technology. Computational spectroscopy combines methods developed at Princeton University, University of Oxford, and Tokyo Institute of Technology to simulate excited-state potential energy surfaces.

Types of Photochemical Reactions and Mechanisms

Photochemical transformations include photoinduced electron transfer studied by groups at IBM Research, photodissociation investigated at facilities like Los Alamos National Laboratory, and photoisomerization characterized in work from ETH Zurich and University of Basel. Chain reactions, such as those exploited in industrial processes at BASF and Shell, rely on radical initiation via photolysis. Photocycloadditions, exemplified by [2+2] reactions explored by researchers at University of Chicago, and Norrish-type cleavage mechanisms analyzed by teams at University of Leeds illustrate mechanistic diversity. Sensitization and quenching phenomena were elucidated in collaborations involving DuPont and academic groups at McGill University.

Applications and Technologies

Practical outcomes include photovoltaic devices advanced by consortia at MIT, Stanford University, and National Renewable Energy Laboratory; photocatalytic water splitting efforts coordinated with Toyota Research Institute and Oak Ridge National Laboratory; and photodynamic therapy developed in clinical research at Mayo Clinic and Memorial Sloan Kettering Cancer Center. Photoresists and photolithography underpin semiconductor fabrication at firms like Intel and TSMC and were refined alongside tools from ASML. Photochemical synthesis enables fine-chemical routes used by Pfizer and Roche, while light-driven molecular machines reflect work awarded by the Nobel Prize in Chemistry and carried out at University of Groningen and The Scripps Research Institute.

Environmental and Biological Photochemistry

Photochemical processes shape atmospheric chemistry studied by researchers at NASA Goddard Space Flight Center, European Space Agency, and institutes such as National Oceanic and Atmospheric Administration. Photolysis of pollutants, ozone photochemistry, and smog formation were characterized in campaigns organized with participation from World Meteorological Organization and Environmental Protection Agency. In biology, photoreceptors and photosystems were resolved by structural biology teams at Max Planck Institute for Chemical Energy Conversion and Salk Institute; processes like photosynthesis and DNA photodamage have been explored by investigators affiliated with Rockefeller University and University of California, San Diego. Photochemical remediation and light-driven sterilization are implemented in programs at World Health Organization and municipal water facilities coordinated with UNICEF.

Category:Chemistry