Dimer fluorescence

Zhu H, Clark SM, Benson SC, Rye HS, Glazer AN (1994) High-sensitivity capillary electrophoresis of double-stranded DNA fragments using monomeric and dimeric fluorescent intercalating dyes. Anal Chem 66 1941-1948. 

A typical emission trace for XeF is shown in Figure 5a, for 500 Torr of xenon and 0.50 Torr of SF. This curve has several components a X-ray signal, dimer rare gas fluorescence and ionic recombination formed exciplex fluorescence. The X-ray signal followed the time profile of the 3 ns. electron pulse, and was typically only a few percent of the total emission signal. The first emission peak was also observed in irradiated pure xenon, at all wavelengths across and outside the XeF emission spectrum, and was therefore assigned to the broad xenon dimer, Xe2 fluorescence. The decay of the dimer fluorescence was typically complete within several hundred nanoseconds, and its intensity varied greatly with the xenon pressure. The second peak in the emission curve was dose-dependent, and only observed across the known XeF ... 

By addition of a dissociative thermal electron capturing gas such as CH2Brj, which quantitatively produces the atomic Br anion, the three body recombination process for an anion can be determined in isolation of any two-body mutual neutralization reactions. For irradiated xenon-CH2Br2 gas mixtures, the total emission at 282 nm was foxmd to consist of X-rays, xenon dimer fluorescence, and XeBr (B,C) exciplex fluorescence formed from both ionic recombination and xenon excited-state reaction [67]... 

As for XeF the X-ray component for irradiated Xe/CH2Br2 was negligibly small. The xenon dimer fluorescence was typically complete within 100 ns and its intensity was proportional to the xenon pressure. The exciplex fluorescence formed by the reaction of excited xenon atoms with CH2Br2 was also observed within the first hundred nanoseconds, however its intensity was strongest at low xenon pressures. The ionic recombination formed exciplex fluorescence again had the slowest rate of production, being observed for many hundreds of nanoseconds. Its intensity was also dependent on total xenon gas pressure being comparable to the excited-state formed fluorescence at low... 

Fluorescence emission data of the diporphyrins also are given in Table I the Q(0,0) band is red shifted and fluorescence yield is decreased. Although some reduction in is predicted by the exciton model (9), the extent of quenching found in the diporphyrins is certainly impressive. It is likely that the enormous red tail of the Soret band further enhances the self quenching of the dimer fluorescence yield. 

Self-assembly principles of the formation of multiporphyrin arrays are extended to anchor the porphyrin triads on semiconductor CdSe/ZnS quantum dot (QD) surface. Comparing with individual counterparts (QD, pyridylsubstituted porphyrin H2P(p-Pyr)4, and Zn-octaethylporphyrin chemical dimer (ZnOEP Ph), the formation of heterocomposites QD-porphyrin triad results in the specific quenching of QD photoluminescence, accompanied by the dimer fluorescence strong quenching (Tsd 1-7 ps due to energy and/or electron transfer) and the noticeable decease of the extra-ligand H2P(p-Pyr)4 fluorescence efficiency by 1.5-2 times via hole transfer H2P—>dimer. 

Typically, for porphyrin triads (ZnOEP)2Ph H2P(p-Pyr)2 the deactivation pathways may be presented as follows [5]. The dimer fluorescence shows the strong quenching (fluorescence decay is shorten from tSd°= 115 ns down to TSD 1.7ps in toluene at 295 K) caused by both S-S energy transfer (rate constant k5= 6.7xlOlo-7.5xlO10 s 1, Fig. 1) and the photoinduced electron transfer (rate constant k() > 8x IO10 s"1). Fluorescence spectra of the triads mainly... 

A number of aromatic hydrocarbon derivatives have been used as fluorophores, but probably the most widely used analogue is pyrene. Pyrene exhibits a strong fluorescent emission band, but when paired with another fluorophore, such as pyrene itself, it exhibits excimer fluorescence. Various applications have indeed used this monomer to dimer fluorescence... 

Figure 6.8 Excimer formation (2). Relative intensities of pyrene fluorescence in benzene as a function of pyrene concentration c in M. Open circles represent relative intensity of monomer fluorescence (///fl) filled circles represent relative intensity of dimer fluorescence (/ //q). From Ref. [22,d).

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