Luminescence behavior

Single emission at 675 (exc 455) Single emission at 575 (exc 465 nin) Figure 3.18 Au TI complexes obtained by condensation reactions and their respective luminescent behavior. 

Balch AL (2007) Remarkable Luminescence Behaviors and Structural Variations of Two-Coordinate Gold(I) Complexes. 123 1-40... 

The first photophysical investigation performed on stereochemically pure metal-based dendrimers having a metal complex as the core is that concerning the tetranuclear species based on a [Ru(tpphz)3]2+ core (tpphz=tetrapyrido[3,2-a 2, 3 -c 3",2"-h 2",3"j]phenazine) [67]. Dendrimer 45 is an example of this family. In this compound, two different types of MLCT excited states, coupled by a medium- and temperature-dependent photoinduced electron transfer, are responsible for the luminescence behavior. However, the properties of all the optical isomers of this family of compounds are very similar. This finding is also in... 

The related reaction shown in Equation (104)117 leads to a butterfly arrangement with two thallium ions bridging between two gold atoms, 127. Here, the Tl-Tl distance is 360.27 pm and is thought to contribute significantly to the physical properties of the complex. The compound shows solvent-dependent luminescent behavior in solution as well as in the solid state. 

R. F. Steiner, Varying luminescence behavior of the different tryptophan residues of papain,... 

Working with titanite, one sample has been found with luminescent behavior strongly different from the others. Suspicion was raised that its identification is not correct. In order to check it, LIBS and Raman data have been received from the same area where liuninescence spectra were determined. Figure 9. la demonstrates that breakdown spectra of titanite are really characterized by the group of UV fines at 300 nm of Ti and by many fines of Ca, the strongest ones at 393 and 396 nm. Nevertheless, such fines are absent in the LIBS of the suspicious sample, where only a strong fine of Na presents at 589 nm and its Raman spectrum (Fig. 9.1c) is totally different from those of titanite (Fig. 9.1b). Subsequent EDX and XRD analyses enabled us to identify this mineral as catapleite. 

In order to improve the luminescence behaviors and obtain better quantum yields, Zhang et al. [245] have suggested a reflux treatment by diluting w/o microemulsions of CdS nanoparticles with the same w/o microemulsions but substituting the reactant solution with H2O. The water in the w/o microemulsion droplets was removed by the co-surfactant (n-hexanol), the trap sites on the nanoparticle surface decreased improving the crystalHnity and thus the fluorescence efficiency. 

Photoinduced electron transfer from eosin and ethyl eosin to Fe(CN)g in AOT/heptane-RMs was studied and the Hfe time of the redox products in reverse micellar system was found to increase by about 300-fold compared to conventional photosystem [335]. The authors have presented a kinetic model for overall photochemical process. Kang et al. [336] reported photoinduced electron transfer from (alkoxyphenyl) triphenylporphyrines to water pool in RMs. Sarkar et al. [337] demonstrated the intramolecular excited state proton transfer and dual luminescence behavior of 3-hydroxyflavone in RMs. In combination with chemiluminescence, RMs were employed to determine gold in aqueous solutions of industrial samples containing silver alloy [338, 339]. Xie et al. [340] studied the a-naphthyl acetic acid sensitized room temperature phosphorescence of biacetyl in AOT-RMs. The intensity of phosphorescence was observed to be about 13 times higher than that seen in aqueous SDS micelles. 

Lindholm and Adamson144 report that photochemically, coordinated NH3 is preferentially lost from Cr(NH3)5NCS2 + while thermally NCS" is replaced. A study of the temperature dependence of Cr(NCS)e3- phosphorescence was reported.145 A general discussion of the luminescence behavior of coordination complexes has been given146 and a careful study of the Cr(C204)33 luminescence spectra has been reported.147... 

CH2py) = l-methyl-3-(2-pyridinylmethyl)-imidazolium] (Figure 2.57a) whose luminescent behavior has been described [307], 2-bis(trimethylsilyl)methylpyridyl [308] or 2-(dimethylaminomethyl)ferrocenyl [309] complexes. In the dinuclear derivative with the 4,5-dihydro-4,4-dimethyl-l,3-oxazol-2-yl)thien-3-yl ligand (Figure 2.57b) the gold-gold distance is 2.8450(6) A [310]. 

Similarly to the results observed in the previous case, the structural differences affected the optical properties of the complexes. While in the former a single emission was observed in the solid state, both at room temperature (440, exc. 390 nm) and at 77 (460, exc. 360 nm) the latter showed one band (510, exc. 450 nm) and one shoulder (560 nm) at room temperature, and two independent emissions (510, exc. 370 nm 550, exc. 480 nm) at 77 K. This pentachlorophenyl derivative was also luminescent in solution, displaying a band at 530 nm (exc. 345 nm), which was not present in the precursor complexes or in the pentafluorophenyl derivative. Therefore, in this case, as in the previous one, it is proposed that the TI H interaction in the solid state remained in solution and was responsible for the luminescence behavior observed in this state. 

Our motivation for offering a further consideration of excimer fluorescence is that it is a significant feature of the luminescence behavior of virtually all aryl vinyl polymers. Although early research was almost entirely devoted to understanding the intrinsic properties of the excimer complex, more recent efforts have been directed at application of the phenomenon to solution of problems in polymer physics and chemistry. Thus, it seems an appropriate time to evaluate existing information about the photophysical processes and structural considerations which may influence excimer formation and stability. This should help clarify both the power and limitations of the excimer as a molecular probe of polymer structure and dynamics. 

Combined with photoemission, DRS provides quantitative data on excitation-luminescence behavior of powdered specimens which can be used to determine photoluminescence quantum efficiencies and the extent of resonant energy transfer among the bulk and surface activators and sensitizers. 

We have seen from the above work that the nonradiative rate constants dominate the luminescence behavior of ruthenium(II) complexes. If one can increase the value of the radiative rate constant, kr, without substantial increases in knr, then emission efficiency can be improved. The radiative rate constant is, in theory at least, related to the molar absorption coefficient, epsilon187. Demas and Crosby188, made a number of assumptions and calculated radiative lifetimes based on observed epsilon values, which were in good agreement with the experimental kr values. Watts and Crosby1895 went on to comment on the possible implications of the epsilon value. 

Luminescence Behavior of Polynuclear Metal Complexes of Copper (I), Silver (I), and Gold (I)... 

Other recent work on the temperature dependence of the luminescence behavior of Os(II) diimine complexes was reported by Ogawa and coworkers in the investigation of [Os(bpy)2(4,4/-dcbpy)] and [Os(bpy)2(3,5-dcbpy)], where 4,4 -dcbpy = 4,4/-dicarboxy-2,2/-bipyridine and 3,5-dcbpy = 3,5-dicarboxy-2,2/-bipyridine. The 4,4 -dcbpy complex exhibited a decrease in the luminescence lifetime with increasing temperature and had an activation barrier of approximately 350 cm x. The luminescence lifetime of the 3,5-dcbpy complex, however, increased with increasing temperature. This surprising observation remains unexplained [14]. 

A bimetallic Os(II) complex of the macrocyclic ligand MAC1 (Scheme 2) was prepared and characterized by Venturi et al. Each Os(II) center of the complex has a [(bpy)20s(II)] fragment attached to one of the bipyridyl units of MAC1. The complex has absorption and luminescence behavior reasonably similar to that of [Os(bpy)3]2+ with an absorption maximum of 488 nm and emission with a maximum of 740 nm (trt = 59 ns, 0rt = 0.003). The complex may be used in the development of supramolecular assemblies [23]. 

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