Luminescent effect

Most dyes and pigments owe their colour to the selective absorption of incident light. In some compounds, colour can also be observed as a result of the emission of visible light of specific wavelengths. These compounds are referred to as luminescent. The most commonly encountered luminescent effects are fluorescence and phosphorescence. The transitions which can occur in a molecule exhibiting either fluorescence... 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

The imidazopyrazine substructure occurs in luciferins from a wide range of organisms living in the sea and in ostracod crustaceans, e.g. Cypridina. The chemistry of the luminescent effect in these systems involves reaction with oxygen to form a stable cyclic dioxetanone, similar to the hrefly luciferin as indicated in (3.108). 

The photophysical effects and mechanisms described in general terms in the above sections will now be illustrated with the aid of findings and interpretations from the world of dendrimers. Since straightforward luminescence effects are also mentioned elsewhere in this book in the context of syntheses (Chapter 2) and the individual types of compounds (Chapter 4) and are, moreover, considered as part of more complex events in Section 5.2, just a few characteristic examples of fluorescence and phosphorescence of dendrimers will be presented The adjacency of many groups in a molecule may lead to the occurrence of complex processes, which sometimes make it difficult to draw precise conclusions, but may sometimes also be useful and amenable to optimisation for various applications. 

While investigating the nature of cathode rays produced in a Crookes mbe that he had covered with a shield of black cardboard, ostensibly to prevent the cathode rays from escaping, Roentgen (Fig. 3.17) observed in 1895 the luminescent effect on a... 

Working with hydroxyethyl cellulose the same author showed that gas removal starts concomitantly with cavitation, the fact proved by the luminescence effect. Figure 3.389 [1147, 1148],... 

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