Luminescence organic ligands

The disadvantages of organic dyes (low photostability, insufficient brightness, short lifetimes, etc.) have resulted in competition from luminescent metal-ligand complexes, semiconductor nanoparticles (Quantum Dots), and conjugated polymers. These new materials show advanced performance in a variety of applications... 

The measurement of equilibrium constants is a crucial aspect in lanthanide and actinide chemistry. Several techniques are available for such determination (spectrophotometry, potentiom-etry, solvent extraction, electrospray mass-spectrometry,. ..), among which TRES is commonly used in the case of reaction studies of luminescent lanthanides with organic ligands (Richardson, 1982 Parker and Williams, 1996). The high sensitivity of TRES (see sect. 6) allows quantitative measurements of very dilute solutions, which facilitates the handling of highly radioactive materials such as Cm. 

When looking for R(III) determination, use can be made of the antenna effect already discussed in sect. 3.7, provided the lanthanide of interest is luminescent. The basic principle is to add a given organic ligand, which will ensure a high complexation constant with the lanthanide together with an efficient UV absorption and energy transfer to the R(III)... 

As it is well known, sensitization of Ln-centered luminescence can be achieved via an intramolecular energy transfer upon excitation of organic ligands, instead of using direct excitation of the weak Lnm absorption bands. This phenomenon now called antenna effect or luminescence sensitization has first been observed in 1942 by Weissman for europium(III) complexes formed with salicylaldehyde and with /3-diketonates, more particularly benzoyl-acetonate (ba, 48a), dibenzoylmethanate (dbm, 48b) and wieta-nitrobenzoylacctonatc (47a, fig. 41) (Weissman, 1942). 

At the end of the 1950 s, Crosby and Kasha reported the rather exceptional case of near-infrared luminescence of trivalent ytterbium ion in an 1 3 (Ln L) chelate occurring after intramolecular energy transfer between the organic ligand, in this case dbm (48b), and the lan-... 

Many lanthanide ions exhibit luminescence, emitting radiation from an excited electronic state, the emitted light having sharp lines characteristic of f-f transitions of a Ln + ion. As will be seen later, this can be enhanced considerably by attaching a suitable organic ligand (e.g. a /3-diketonate, phenanthroline, crown ether, etc.) to the lanthanide. 

In this article, a number of selected d-block organotransition metal compounds are introduced and their remarkable luminescence and photochemical properties are described and discussed. Emphasis is placed on the interrelationship between the nature of the transition metal centers, identity and bonding mode of the organic ligands, the photophysical and photochemical properties, and the character of the emissive states. Novel luminescent organotransition metal complexes with potential application values in different areas are also included here. Meanwhile, readers are referred to a selection of book chapters and review articles on the photophysics and photochemistry of transition metal complexes. ... 

Since the dipole strength of/-/ transitions are formally forbidden, typically, these extinction coefficients are of the order of 1 M cm an alternative path has to be used which is called luminescence sensitization or antenna effect, that is when the luminescent ion is coordinated with an organic ligand or imbedded into a matrix, then the energy absorbed will be transferred from the surrounding onto the luminescent ion and subsequently the ion emits characteristic light. 

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