Pure Appl. Chem., 2005, Vol. 77, No. 6, pp. iv
Preface
Photochemistry is a mature science. A characteristic hallmark of a consolidated
scientific discipline is that it increasingly broadens its scope of interests
from an initial central core toward the periphery where it interacts with
other areas. Most of the current scientific research is characterized by
an enriching multidisciplinarity, focusing on topics that combine backgrounds
from different fields. In this way, the largest advances are taking place
at the interphase between areas where different fields meet.
This multidisciplinarity is, I believe, also a characteristic feature of
the current situation for photochemistry. Thus, photochemistry was initially
focused on the understanding and rationalization at a molecular level of
the events occurring after light absorption by simple organic compounds.
Molecular organic photochemistry constituted the core of this discipline,
and it largely benefited from advances in the understanding of the electronic
states provided by quantum mechanics. Later, photochemistry started to grow
toward areas such as photobiology, photoinduced electron transfer, supramolecular
photochemistry, and photochemistry in heterogeneous media, always expanding
its sphere of interest.
This context of increasing diversity in topics and specialization is reflected
in this issue of Pure and Applied Chemistry. The contributors correspond
to some of the plenary plus two invited lectures of the XXth IUPAC Symposium
that was held 17ñ22 July in Granada, Spain. The program included plenary
and invited lectures and oral contributions grouped in 13 sections covering
femtochemistry, photochemistry of biomacromolecules, single-molecule photochemistry,
and computational methods in photochemistry to nanotechnology, among others.
These workshop titles give an idea of the breadth of themes that were included
in this symposium. While it is obvious that the list of contributions correspond
to different subdisciplines in photochemistry, all of them have a common
scientific framework to rationalize the facts.
The purpose of the symposium was to present an overview of the current status
of some research fronts in photochemistry. This issue begins with the 2004
Porter Medal Lecture awarded jointly by the Asian, European, and Interamerican
Photochemical Societies that was given to Prof. Graham Fleming (University
of California, Berkeley) for his continued advances in photosynthesis. Prof.
Flemingís studies have constituted a significant contribution to the understanding
of the interplay between the structure of photosynthetic centers of green
plants and the mechanism of energy migration toward the photosynthetic centers.
These events take place in a very short time scale and are governed by the
spatial arrangement of the constituents.
Continuing with photobiology, the second article by Prof. Jean Cadet (Grenoble
University) describes the type of photochemical damage and photoproducts
arising from DNA UV irradiation. Knowledge of these processes is important
for a better understanding of skin cancer and the possibilities for DNA
repair. Closely related with DNA damage occurring upon irradiation, the
article by Prof. Tetsuro Majima (Osaka University) provides an account of
his excellent work on photosensitized oneelectron oxidation of DNA.
The concept of "conical intersection", developed initially by Robb and Bernardi
to rationalize the relaxation of excited states, led to the foundation of
computational photochemistry, which has proved to be of general application
to photochemical reactions. In this issue, Prof. Massimo Olivucci (University
of Siena) shows that quantum chemical calculations can also be applied to
photochemical reactions occurring in photobiology and, in particular, to
the problem of vision. These calculations are characterized by the large
number of atoms that are included and the fact that they have to estimate
at a high calculation level and with high accuracy the energy of states
differring in a few kcal mol-1.
The next article corresponds to one of the two invited lectures included
in this issue. The one given by Dr. Virginie Lhiaubet-Vallet (Technical
University of Valencia) in the workshop Photophysical and Photochemical
Approaches in the Control of Toxic and Therapeutic Activity of Drugs describes
the enantioselective quenching of chiral drug excited states by biomolecules.
Moving from photobiology to free radical polymerization with application
in microlithography, the article by Prof. Tito Scaiano (University of Ottawa)
reports among other probes an extremely elegant approach to detect the intermediacy
of radicals in photochemical reactions based on a silent fluorescent molecular
probe containing a free nitroxyl radical.
Solar energy storage is a recurrent topic and a long-desired application
of photochemistry. In her comprehensive contribution, Prof. Ana Moore (Arizona
State University) summarizes the continued seminal contribution of her group
to the achievement of an efficient solar energy storage system based on
the photochemical generation of long-lived charge-separated states. Another
possibility of solar energy storage consists of water splitting. In his
article, Prof. Haruo Inoue (Tokyo Metropolitan University) deals with artificial
photosynthetic methods based on the use of ruthenium porphyrins as photosensitizers
for the two-electron oxidation of water with formation of dioxygen.
Also in applied photochemistry, Prof. Luisa De Cola (University of Amsterdam)
reports on intramolecular energy transfer in dinuclear metal complexes having
a meta-phenylene linker. The systems described by Prof. De Cola have potential
application in the field of light-emitting diodes, since most of the complexes
described exhibit electroluminescence. The second invited lecture is by
Dr. Alberto Credi (University of Bologna), one of Europeís most promising
young photochemists. In his interesting article, the operation upon light
excitation of a rotaxane molecular machine is described. A macro-ring acting
as electron donor moiety in a charge-transfer complex is threaded in a dumbbell-shaped
component having two viologen units with different redox potential. Light
absorption produces the cyclic movement of the macro-ring from one viologen
station to the other.
The last two contributions fall within the more classic organic photochemistry
realm. Prof. Axel Griesbeck (University of Cologne) describes the multigram
synthesis of antimalarial peroxides using singlet-oxygen photosensitizers
adsorbed or bonded to polymer matrices. The last contribution comes from
Prof. Heinz Roth (University of Rutgers), who has worked during his entire
career in the fields of organic photochemistry and radical ion chemistry.
Prof. Roth has summarized his vast knowledge in radical ion chemistry, reviewing
the mechanism of triplet formation arising from radical ion pair recombination.
This mechanism for triplet formation is currently gaining a renewed interest
owing to the potential applicability to the development of phosphors.
I hope that the present selection will be appealing and attractive for a
broad audience of readers interested in photochemistry and will give readers
an idea of the state of the art of some current topics in this area.
Hermenegildo García
Conference Editor