Photophysical and photochemical behaviors

The interaction of UV radiation with nucleic acids is of great importance since it can lead to UV-induced damage in DNA with profound consequences, including photocarcinogenesis [1,2]. The nucleobases are the primary chromophores in DNA and RNA, and consequently, the photophysical and photochemical behavior of the nucleobases has been the focus of extensive theoretical and experimental work over the years [4, 6, 81, 82],... 

Dabestani, R., Photophysical and Photochemical Behavior of Polycyclic Aromatic Hydrocarbons on Silica Surfaces, Inter-Am. Photochem. Soc. News ., 20, 24-36 (1997). 

Understandably, there is an enormous richness in the photophysical and photochemical behavior of the excited states present in diimine rhenium tricarbonyl complexes. Indeed, this plethora of molecular photophysical characteristics has led to a wide range of interesting and important applications, including their use as catalysts [21-25], sensors [26-33], probes for photo-polymerization [10, 34, 35], optical switches [36 15], light-emitting materials [46-52], nonlinear optical materials [53-56], binding or photocleavage of DNA [57-61], and radiopharmaceuticals [62-66], Under the purview of this article our focus will be to cover photophysical and photochemical properties and hence other aspects, such as synthetic, catalytic, pharmaceutical, etc., will not be discussed. 

UV filter and finished product photostability are a topic for the synthetic and formulation chemists. Their use of reliable and specific assessment protocols provides an excellent screening tool for development of new ingredients and formulations. Insight into the photophysical and photochemical behavior of the substances/products under study will help to avoid errors in the design of experiments. It is also essential to a meaningful interpretation of data and helps prevent premature disqualification of substances/products, which for instance undergo equilibration when exposed. 

Photophysical and photochemical behavior of the polyacene molecules such as pyrene, anthracene, perylene adsorbed in the cages of X and Y zeolites depend on the cation and hydration degree of zeolites [1-3]. 

Several studies on CD complexes with aromatic molecules using steady-state and nanosecond spectroscopy have been reported. These studies aimed to understand the photophysical and photochemical behavior of organic guests such as fluorescence and phosphorescence enhancement, excimer/exciplex formation, photocleavage, charge and proton transfer, energy hopping, and cis-trans photo-... 

Insight into the mechanism of chemical reactions in solution is in many cases restricted by the limited experimental information available on the details of the individual reaction steps, the possible participation of reaction intermediates, and the nature of the transition state. In addition, information on the nature of the excited state, and its photophysical and photochemical behavior, are essential for the understanding of photoinduced chemical processes. Past experience has clearly shown that our understanding of complex chemical processes can benefit substantially from the application of techniques that reveal either directly or indirectly further information on the intimate chemical mechanism. In this respect, the application of extreme or nonclassical conditions, such as low temperatures and high pressures, has become a powerful tool in the elucidation of thermal and photochemical reaction mechanisms. 

Data on photophysics and photochemistry of intramolecular stilbene-amine exciplexes and reactions have been reported [34]. The obtained data indicated that the photophysical and photochemical behavior of a series of traws-(aminoalkyl) stilbenes in which a primary, secondary, or tertiary amine is appended to the stUbene ortho position with a Me, Et, or Pr linker. The tertiary (aminoalkyl) stilbenes formed fluorescent exciplexes and underwent trans cis isomerization but failed to undergo intramolecular N—H addition. The secondary (aminoalkyl)stilbenes did not form fluorescent exciplexes but underwent the addition to the stilbene double bond. Intramolecular reactions were highly selective, providing an efficient method for the synthesis oftetrahydrobenzazepines. Direct irradiation of the primary (aminoalkyl) stilbenes resulted only in trans-cis isomerization, while irradiation in the presence of the electron acceptor p-dicyanobenzene resulted in regioselective intramolecular N—H addition to the stilbene double bond. 

In this review, we restrict ourselves to metal-mediated assemblies of functional 7T-systems, which absorb light in the visible region (i.e. A. > 400 nm). Thus, materials whose color arises from metal ions or metal-ligand charge transfer (MLCT) are not included here. Self-assembhes derived from free base porphyrins, metalloporphyrins and perylene bisimide dyes have shown promising applications in artificial LH systems. Therefore, some fundamental properties of a few representative chromophores, namely meso-tetraphenylporphyrin (TPP), zinc tetraphenylporphyrin (ZnTPP), tetra-phenoxy-substituted perylene bisimide (PPBI) and bay area imsubstituted perylene bisimide (PBI), are briefly summarized herein. These properties are essential for the understanding of the photophysical and photochemical behavior of assemblies derived from such dyes. 

In fact, it is well known that Cr(lll) polypyridyl complexes are reduced to the labile Cr(ll) species upon irradiation with 351 nm laser, in agreement with their strong oxidant character in the excited state. Flash-photolysis experiments showed transient decay constants in the ps and sub-ps timescale that could be quenched by both, oxidants ([Ru (NH3)6]) and reductants (F, triethanolamine and alcohols) [39]. A very complex photophysic and photochemical behavior were described. 

Lewis, F.D., Reddy, G.D., Bassani, D., Schneider, S., and Gahr, M., Photophysical and photochemical behavior of intermolecular and intramolecular styrene-amine exciplexes, /. Photochem. PhotobioL, A Chem., 65, 205, 1992. 

Functional Cyclodextrin Systems from Spectrophotometric Studies to Photophysical and Photochemical Behaviors... 

Over the last decade, there has been increasing interest in photochemistry in constraining space. If photoactive chromophores are compartmentalized in the hydrophobic microdomains of the unimer micelles, the chromophores will be completely isolated from one another in highly constraining nonpolar microenvironments and protected from the aqueous phase. Owing to these unusual microenvironmental effects, such chromophore-functionalized unimer micelles, unlike the conventional molecular assembly systems, induce a large modification of the photophysical and photochemical behavior of the compartmentalized chromophores. 

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