Page 21 - Photoreactive Organic Thin Films

xx PREFACE

photo-induced mass movement of polymers have also been reported.
Inasmuch as optical ordering of photoisomerizable molecules is being inten-
sively studied, its theoretical quantification helps bridge independent studies
in the areas of nonlinear optics and photochemistry.
Photoisomerization was studied from a purely photochemical point of
view in which photo-orientation effects can be disregarded. While this feature
can be true in low viscosity solutions where photo-induced molecular orienta-
tion can be overcome by molecular rotational diffusion, in polymeric envi-
ronments, especially in thin solid film configurations, spontaneous molecular
mobility can be strongly hindered and photo-orientation effects are appre-
ciable. The theory that coupled photoisomerization and photo-orientation
processes was also recently developed, based on the formalism of Legendre
Polynomials, and more recent further theoretical developments have helped
quantify coupled photoisomerization and photo-orientation processes in films
of polymer.
A number of polymers containing photoisomerizable chrornophores have
been reported, and several authors reported studies in Langmuir-Blodgett-
Kuhn azo-polymers as multilayer structures and alignment layers for liquid
crystal molecules, self-assembled monolayers, amorphous and liquid crys-
talline polymers and so on. In recent years, studies of the role of inter-
chromophore interactions and molecular addressing have been reported, and
questions have begun to arise concerning the relationship of optical ordering
processes in amorphous polymers to the Tg and polymer structure, including
the main chain rigidity, the free volume, and the nature of the connection of
the chromophore to a rigid or a flexible main-chain. These studies correlated
the optical ordering (nonpolar and polar) to the polymer structure in a series
of very high Tg (up to 350 °C) rigid or semirigid NLO polymers, and demon-
strated a new way of probing sub-Tg polymer dynamics in photoreactive
NLO polymers.
These intensive studies on POTF have been performed by a large number
of scientists from a variety of communities, including polymer scientists,
photochemists and photophysicists, chemists and chemical engineers, optical
physicists and optical engineers, and researchers in the field of organic non-
linear optics. Each of these scientists approached POTF research from the
point of view of his or her own field. This book unifies the various sub-
themes of photoisomerization research and bridges different disciplines.
Leading experts have encapsulated their work on POTF research in compre-
hensive and self-consistent chapters. Both fundamental and application issues
are discussed; and the readers, including non-specialists, can not only appre-
ciate that this book represents the largest collection of information on this
topic published in a single book, but also see and eventually acknowledge the
interdisciplinary nature of POTF research and applications. We expect this
book to be the essential reference on POTF science for both students and for
researchers in adjacent fields.

Zouheir Sekkat
Wolfgang Knoll