Luminescence enhancement

The triplet-state energy level of oxytetracycline, the excitation maximum (412 nm), lifetimes of Eu-OxTc (58 p.s) and Eu-OxTc-Cit (158 p.s), were determined. A 25-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. It s accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu(III) and citrate (C = T lO mol-E ), pH 7.2. Eor determination of citrate, the optimal conditions concentrations of Eu(HI) and OxTc are 1 0,5 (Cg = MO Huol-E-i, = 5-10-HuohE-i) at pH 7.2. 

S. Son, A. Dodabalapur, A.J. Lovinger, and M.E. Galvin, Luminescence enhancement by the introduction of disorder into poly(p-phenylene vinylene), Science, 269 376-378, 1995. 

Luminescence Enhancement During Aqueous to Organic Phase Transfer. 345... 

Such systems can undergo ion recognition when made up of a ruthenium or rhenium polypyridyl lumophore and a crown ether receptor for metal ions, similar to the ICT examples given above. There are many examples in the hterature, but one will have to sufhce in this context. Compound (3.85) is interesting because it shows significant luminescence enhancement with Pb. ... 

Cao LX, Zhang JH, Ren SL, Huang SH (2002) Luminescence enhancement of coreshell ZnS Mn/ZnS nanoparticles. Appl Phys Lett 80 4300-4302... 

Martin, N. Biinzli, J.-C. G. McKee, V. Piguet, C. Hopfgartner, G. Self-assembled dinuclear lanthanide helicates substantial luminescence enhancement upon replacing terminal benzimidazole groups by carboxamide binding units. Inorg. Chem. 1998, 37, 577-589. 

A completely new source of electrochemiluminescent compounds may have been recently discovered as well. Weak luminescence was observed from fluids extracted from tunicates, a type of marine invertebrate, and synthetic tu-nichromes (the chromophore in the tunicates) upon oxidation [66], The structure of the synthetic tunicate chromophore is shown in Fig. 13. A 10-fold enhancement of ECL is observed when the synthetic analogues of the tunichromes are complexed to Hg2+. The mechanism of the luminescent enhancement has not yet been elucidated. 

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

In a second report on the cyclen analogue 34, binding of lactate to the Tb(III) complex was found to be aided by the presence of the aza-crown when compared to the TbD03A control. Studies of 34 with benzoate and salicylate in buffered solutions at pH 7.4 showed luminescence enhancements of 12-fold (log ft = 2.9) and 135-fold (log f) = 3.9), respectively. When compared to Tb D03A, with luminescence enhancements of only 14-fold (log ft = 2.7)... 

Another related example is 52 [157], which is a tetra-substituted cyclen ligand with four quinoline receptor moieties capable of sensing protons in a similar manner to 50. The lanthanide emission was found to be switched on in highly acidic conditions, with a luminescent enhancement of over 300-fold. Luminescent enhancement was attributed to an enhancement in the population of the Si and subsequent Ti excited states of the quinoline chromophore when in acidic media. A bell-shaped pH profile was found to exist at pH 1.8-3.5, whereas at more acidic pH the emission was switched off. 

Other groups have subsequently reported anion receptors that work on the same principle. For instance, an Eu(III) complex of the bis-bipyridinephen-ylphosphine oxide ligand 86 made by Ziessel and co-workers is able to sense anions by luminescence enhancement in acetonitrile, with stability constants which follow the trend fluoride>acetate>chloride>nitrate [61]. Tsukube and co-workers have investigated the properties of the Eu(III) and Tb(III) complexes of the chiral ligand 87 [62]. Anion binding was assessed by profiling luminescence enhancement in acetonitrile, and it was found that the different metal centres provided different selectivities. The emission at 548 nm of the Tb(III) complex was increased by 5.5 times in the presence of 3 equivalents of chloride compared to 2.2 for nitrate and 1.1 for acetate. Conversely the emission at 618 nm of the Eu(III) complex was increased 8.3 times by 3 equivalents of nitrate, 2.5 times for chloride and 1.0 times for acetate. Stability constants were not reported. 

Another possibility is to take advantage of the effect of various supporting electrolytes (in a wide sense) that act as luminescence enhancers, as discussed in sect. 3.3, such as phosphoric acid. This method has been investigated in details both for lanthanides and actinides... 

Determined with lb0Tb3+. All others determined by Tb3+ luminescence enhancement bNot available. 

---