Luminescent state

However, the case of luminescence of PET fibers and films is not so easily interpreted and has recently been the subject of several studies (2,7,9,21,22,23). There is general agreement that PET does have a luminescent state and that the observed emission is not merely an impurity. The origin of the fluorescence has remained the subject of debate for the past decade. 

Genotoxicity may also be tested with a Mutatox test (Azur Environmental Ltd., Berkshire, England), using a dark mutant strain of bioluminescent bacterium V. fischeri [54]. DNA-damaging substances are recognized by measuring the ability of a test sample to restore the luminescent state in the bacterial cells. The authors pointed to the sensitivity of the test to chemicals that damage DNA, bind DNA, or inhibit DNA synthesis. 

Mixed complexes of bq, pq and DMCH with bpy and phen have also been studied52,147"149,223,250. In all cases luminescent states appear to be localized with emis-... 

Luminescence from Cr + complexes, both in the solid state and in solution, is a widespread phenomenon. The great majority belong to type a) in Figure 1, where the luminescent state is 2E and the optical transitions are sharp. The well-known ruby emission is a prototype for this situation. In a weaker ligand field the situation b) in Figure 1 is approached, the T2 state becomes competitive with E as the luminescent state. The T emission, corresponding to a spin-allowed d-d transition, is vibronically broadened. Pure 2 luminescence from Cr + has been observed in halide and oxide coordinations (J ). Intermediate situations with both 2E and 2 emissions ar also known. 

Figure 7. Equilibrium geometry of luminescent state of Cr + in Cs2NaYCl6.

The nature of the photoreactive state, as opposed to the luminescing state, is still the source of some debate, as states other than the lowest triplet have been proposed to be important. Evidence that an excited singlet may be involved comes from time-resolved studies of the luminescence of some haloammine complexes, where a weak fluorescence, with a lifetime of about lOOps, was... 

Dendrimer-type ligand (32) serves as a lanthanide container to exhibit on-off switchable luminescence upon lanthanide complexation in response to external anions [56]. Because of the presence of two classes of coordination sites for the lanthanide cations at the inner and outer spheres, the dendrimer 32 exhibits two different binding modes to afford on-off lanthanide luminescence, in which outer complexation at the tetradentate tripod site offers the on luminescence state upon quinoline excitation whereas, inner complexation at the multidentate core site corresponds to the off luminescence state. Upon complexation of 32 with Yb(CF3 SO3 )3, the quite weak NIR luminescence from the Yb(III) center suggests that the Yb(III) ion is most probably located at the inner coordination sites and apart from the excited quinoline moieties. Nevertheless, addition of SCN anion to the 32-Yb(CF3803)3 system induced remarkable spectral changes around the quinoline absorption band and about ninefold enhancement in luminescence intensity at around 980 nm. As the intense Yb luminescence appeared upon quinoline excitation, the employed SCN anion promoted the tripod-Yb +... 

The NIR emission intensity of the lanthanide porphyrinate complexes follows the trend Yb > Nd > Er. This agrees with observations on other luminescent lanthanide complexes and reflects the fact that the efficiency of nonradiative decay increases as the energy of the luminescent state decreases. The emission yields of the ternary lan-thanide(III) monoporphyrinate complexes with hydridotris(pyrazol-l-yl)borate or (cyclopen-tadienyl)tris(diethylphosphito)cobaltate as a co-ligand are generally higher than those of other Yb(III), Nd(III), and Er(III) complexes because the coordination environment provided by the porphyrinate in combination with the tripodal anion effectively shields the Ln + ion from interacting with solvent (C-H) vibrational modes that enhance the rate of nonradiative decay. 

Optical measurements have been reported for [Ru(bipy)3], [Ru(bipy)2(biq)f, and [Ru(biq)3] (biq = 2,2 -biquinolyl) together with the temperature dependence (84—330 K) of the luminescence emission. The behaviour of the three complexes is rationalized in terms of states derived from a simple orbital model. A description of the photophysical and redox properties of the luminescent complexes [RuLL L ] (where L = 2,2 -bipyridyl, L = 2,2, 2"-terpyridyl, and L" = phenothiazine, N-methylphenothiazine, thian-threne, or H2O) has appeared, and this suggests that states other than the luminescent state are populated. Coupling between dissimilar ligands in the excited states of [Ru(bipy) (phen)3 f, [Ru(bipy) L3 and... 

The parent complex, cls-IrCl9(phen) , has an essentially pure MLCT emitting level. The decay constants of this state are similar to those of the MLCT emitting states of the bipy series. The luminescent state of IrCl2(5,6-dlmethylphen)2 , however, has almost complete IL character. As expected for ligand localized transitions, the radiative and nonradlative rate constants of this state are much smaller than those of the MLCT emitting states in the bipy system (Table 9). The emitting levels of the other substituted phen complexes are proposed to have fairly equal contributions from the zero-order IL and MLCT states (194). 

In photochemical reduction of CO2 by metal complexes, [Ru(bpy)3] is widely used as a photosensitizer. The luminescent state of [Ru(bpy)3] is reductively quenched by various sacrificial electron donors to produce [Ru(bpy)3] . Metal complexes used as catalyst in the photochemical reduction of CO2 using [Ru(bpy)3] are prerequisites which are reduced at potentials more positive than that of the [Ru(bpy)3] " redox couple (-1.33 V vs SCE) (72). Irradiation with visible light of an aqueous solution containing [Co (Me4(14)-4,ll-dieneNJ], [Ru(bpy)3], and ascorbic acid at pH 4.0 produces CO and H2 with a mole ratio of 0.27 1 (73). Similarly, photochemical reduction of CO2 is catalyzed by the [Ru(bpy)3] /[Ni(cyclam)] system at pH 5.0 and also gives H2 and CO. However, the quantum efficiency of the latter is quite low (0.06% at X = 400 nm), and the catalytic activity for the CO2 reduction decreases to 25% after 4 h irradiation (64, 74, 75). This contrasts with the high activity for the electrochemical reduction of CO2 by [Ni(cyclam)] adsorbed on Hg. 

By the late 1970s I had looked at the luminescence spectra of a large number of chromium(III) compounds and I was looking for new systems to study. One approach was to look at the well-known emission from uranyl compounds, but just after we started work on them Denning and colleagues solved the most pressing problem of the identity of the lowest (i.e. luminescent) state in a series of beautiful... 

Arfsten DP, Davenport R, and Schaffer DJ, Reversion of bioluminescent bacteria (Mutatox ) to their luminescent state upon exposure to organic compounds, munitions, and metal salts, Biomed. Environ. Sci., 7, 144, 1994. 

The complex anion of [Pt2(pop)4] has a strong singlet absorption band associated with a weakly luminescent state, A2 Aig (d(7 p8), which can... 

TABLE 6. Decay Rate Constants of the Metal Luminescent States and Number of Solvent Molecules Coordinated to the Metal Ion11... 

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