Photophysical-photochromic

Ultraviolet absorption spectra were also applied in the investigations on photophysical, photochemical, and photochromic behavior of some... 

The insensitivity of so many of the photophysical and photochemical properties to proteolytic degradation down to about half of the original molecular weight is remarkable. It is particularly noteworthy when the location of the bilatriene chromophore near the N-terminus—one of the sites of preferential endogenous proteolytic attack—is taken into account and also the fact that the photochromic behavior of chromopeptides obtained by further protein degradation progressively deteriorates and is eventually lost [8b],... 

The monolayer also provides an environment of variable dielectric so that intermolecular association between photoactive molecules can readily occur. For example, molecular association of pyrene within a Langmuir-Blodgett film is clearly seen through time-resolved fluorescence measurements on the picosecond timescale [92], Attenuated total reflectance studies of dyes in cast films can similarly reveal their positions and photophysical interactions [93], Photochromism in a monolayer assembly has been attributed to excitation of ion-pair charge transfer complexes formed within the array [94]. 

C. Lenoble and R. S. Becker, Photophysics, photochemistry and kinetics of photochromic 27 -pyrans... 

The photochromism of dihydroindolizines (DHIs) - a new class of photo-chromic molecules - was discovered only in 1979.1,2 These molecules are among the few new photochromes discovered in the past 20 years.3 Their synthetic access has been exploited in detail and their photochemical and photophysical parameters have been studied in a broad sense.3 7 The potential applications are vast and compare favorably with those of the known photochromes.8 The chemistry and photochemistry of the DHIs have been described previously in several surveys.3-7 This review will serve as a short introduction to the field. It will as well include typical preparation modes for the class of dihydroindolizines as well as their aza-homologs, typical five-membered heterocycles. A new class of photochromies derived from these photochromic heterocycles (DHIs) that allows for supramolecular interactions is presented. Some typical applications that are close to commercially useful systems are discussed. 

Topics which have formed the subjects of reviews this year include theoretical studies of the photochemistry of thiiranes, photoaddition of amines to aryl olefins and arenes, the synthesis of heterocyclic compounds, photoamination directed towards the synthesis of heterocycles, selective addition of organic dichalcogenides to carbon-carbon unsaturated bonds, photocyclisation mechanisms of c/5-stilbene analogues, synthetic utility of the photocyclisation of aryl-and heteroarylpropenoic acids, photochromic diarylethenes, spiropyrans, cy-clophanes, and polycondensed aromatics," photochromic organic media, photophysics and photochemistry of P-carbolines, and the photochemical synthesis of macrocycles.Chirality switching by light has also been described. ... 

Topics that have formed the subjects of reviews this year include contemporary issues in electron transport research, dynamics of bimolecular photoelectron transfer reactions, photophysical properties of functionalised fullerene derivatives, carbon-carbon bond formation via radical ions, photoinduced electron transfer processes in ketone, aldehyde, and ester synthesis, photochemical reactions between arenenitriles and benzylic donors, photo-oxidation of conjugated dienes, photoredox reactions of aromatic nitro compounds, electron transfer-mediated photochemistry of some unsaturated nitrogen-containing compounds, reactions of 02( Ag), carbon dioxide activation by aza-macrocyclic complexes, and photochromism of chalcone derivatives. ... 

The technical improvements in physicochemical investigations of photochromic behavior combined with the synthesis of new interesting models of photochromic substances are anticipated to lead to new advances in the knowledge of the very complex phenomenon that is photochromism, regardless or independently of the various suggested photophysical mechanisms for photocoloration. 

R. Kaufman, D. Levy, and D. Avnir, Photophysical studies of the sol-gel transition in silica Structural dynamics and oscillations, room temperature phosphorescence and photochromic gel glasses,/. Non-Cryst. Solid82, 103-109 (1986). 

A. Kellmann, F. Tfibel, R. Dubest, P. Levoir, J. Aubard, E. Pother, and R. Guglielmetti, Photophysics and kinetics of two photochromic indolinospirooxazines and one indolinospironaphthopyran, J. 

The specific structural features of SPs affect the photochromic properties of these compounds. Since photophysical and photochemical properties of organic molecules depend essentially on their structure in the excited state, we shall examine the nature of the structural changes in these molecules upon photoexcitation. The nature of such changes, in turn, depends on the type of electronic transition that converts the molecule into a photochemically active state (PCAS). The converstion of SP1-SP4 molecules to a PCAS upon UV irradiation with k > 300 nm is known to be due to electronic transitions of the n-n type in molecules without EA substituents and of the nn -jt 7t type in molecules with EA substituents in the benzopyran moiety.29 These transitions are characterized by intramolecular charge transfer (ICT), mainly from the l orbital of the oxygen atom and the 7t orbital of the C(3)=C(4) bond to the phenyl group and the EA substitutents. 

The photoirradiation of (9) covalently bound to porphyrin induces irreversible cis,trans-isomerization The influence of picric acid on the photochemical tmns,c/s-isomerization of 4-(4 -dimethylaminostyryl)pyridine has been evaluated. Details about the photophysical and photochemical behaviour of trans-di-(2-naphthyl)ethene have been published. The styryl dye (10) has been synthesized and its photochemistry and photochemical properties studied. The photochromic properties depend upon the cis,trans-isomerization and also on (2 + 2)-cycloaddition processes. ... 

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