The Concept of Molecular Photonics

In order to understand the concept of Molecular Photonics, it is crucial for the reader to undertake a study of fundamental principles. Chapter 1 Fundamentals of Molecular Photonics includes four sections dedicated to optics, the molecular field theory, the radiation field theory, and the interactions between the molecular field and the radiation field. Fundamental principles are often treated in an introductory chapter, leading the reader to think that they are of little importance and that they can be understood with ease. This trend of relegating the fundamentals to a brief introduction is getting increasingly common in natural 

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In this chapter we will attempt to uncover the events, in recent history, that led to the formulation of the concept of Molecular Photonics. What are the research areas supported by the concept of Molecular Photonics What are the relationships between the fundamental fields described previously and Molecular Photonics These questions need to be answered. We will draw a picture of Molecular Photonics starting form several related fields (see Table 0.3). 

This situation has led an artificial distinction between the physicists approaches, dealing with the interaction between the radiation field and the molecular system, and the chemists approaches towards the study of photophysical chemistry and photochemistry. This arbitrary separation has to be destroyed to understand fully the concepts of molecular photonics. 

Science philosophers often argue about the relative merits of the analytical and synthetic approaches to scientific research. A synthetic viewpoint cannot be created without analysis, and conversely, the systemization and development of a theory necessitates analysis. Analysis is a scientific tool or method which becomes meaningful only if it derives from a synthetic view of phenomena probed by experiments. The proposed new concept of Molecular Photonics cannot escape this methodology. It may be seen as a dogma at first. But through... 

The concept of molecular electronics describes an interdisciplinary research area which deals with the questions of how molecular systems and molecular materials might find applications in electronics, photonics, and optoelectronics. We can perhaps define molecular electronics as follows it includes those processes and phenomena in which organic molecules, individually or in larger numbers, play an active role in the processing, transferring and storage of information [1-5]. 

Between 1923 and 1927, the concepts of quantum efficiency (number of photons emitted divided by number of photons absorbed by a sample) and quantum yield (fraction of excited molecules that emit) had been defined and values determined for many compounds by Vavilov (34). The quantum yield indicates the extent that other energy loss mechanisms compete with emission in an excited molecule. Although the quantum yield is influenced by the molecular environment of the emitter, for a given environment it depends on the nature of the emitting compound and is independent of concentration and excitation wavelength, at least at low concentrations (35). Tlius, it serves as another measurable parameter that can be used to identify the compounds in a sample and also, because of its sensitivity to the surroundings of the luminophore, to probe the environment of the emitter. 

Outside of a small region around the center of the Brillouin zone, (the optical region), the retarded interactions are very small. Thus the concept of coulombic exciton may be used, as well the important notions of mixure of molecular states by the crystal field and of Davydov splitting when the unit cell contains many dipoles. On the basis of coulombic excitons, we studied retarded effects in the optical region K 0, introducing the polariton, the mixed exciton-photon quasi-particle, and the transverse dielectric tensor. This allows a quantitative study of the polariton from the properties of the coulombic exciton. 

Fig. 8 Molecular orbital depiction of the concept of band-gap energies with corresponding molecular orbital transitions for the Fe(III) oxyhydroxides. The photon action spectra [134,230] for photochemical reactions [136,141,143] of the iron oxyhydroxides (i.e., a-Fe2C>3, a-FeOOH, /S-FeOOH and y-FeOOH) indicate that the most effective electron transition leading to photocatalysis or photoreduction is the O2- to Fe3+ transition shown schematically above...

We have examined the photolysis of heme groups that are incidentally photosensitive. The heme proteins form a special class of proteins yet some rather important results have come from studies from them. Do these results have general validity We will in this section drift a bit from the subject of photolysis (the rupture of a molecular bond by absorbed photon) and discuss briefly other laser excitation techniques that we believe help us understand the concepts of protein rigidity and the... 

Multifunctional materials will play an important role in the development of Photonics Technology. This paper describes novel multifunctional polymeric composites for applications in both active and passive photonic components. On the molecular level, we have introduced multifunctionality by design and synthesis of chromophores which by themselves exhibit more than one functionality. At the bulk level, we have introduced the concept of a multiphasic nanostructured composites where phase separation is controlled in the nanometer range to produce optically transparent bulk in which each domain produces a specific photonic function. Results are presented from the studies of up-converted two-photon lasing, two-photon confocal microscopy, optical power limiting, photorefractivity and optical channel waveguides to illustrate the application of the multifunctional optical composites. 

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