Fluorescence excimer

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

By examining any correlation between excimer formation (as evidenced by characteristic excimer fluorescence) and dimerization quantum yield, one could perhaps determine whether dimerization is dependent upon prior excimer formation. Excimer fluorescence from anthracene solutions at room temperature is negligible although it has been observed in the solid state at low temperature.<75) Unfortunately, the data for substituted anthracenes allow no firm conclusions to be drawn. Some derivatives dimerize but do not exhibit excimer fluorescence. Others both dimerize and show excimer fluorescence. Still others show excimer fluorescence but do not dimerize and finally, some neither dimerize nor show excimer fluorescence. Hopefully, further work will determine what role excimer formation plays in this photodimerization. 

Evidence for the role of a singlet excimer in the formation of (78) was provided by the observation of excimer fluorescence from dilute solutions of coumarin in methylcyclohexane and isopentane glasses at 77°K.(93b)... 

Sahoo D, Narayanaswami V, Kay CM, Ryan RO (2000) Pyrene excimer fluorescence a spatially sensitive probe to monitor lipid-induced helical rearrangement of apolipophorin III. Biochemistry 39 6594-6601... 

Okamoto A, Ichiba T, Saito I (2004) Pyrene-labeled oligodeoxynucleotide probe for detecting base insertion by excimer fluorescence emission. J Am Chem Soc 126 8364—8365... 

Kostenko E, Dobrikov M, Phshnyi D, Petyuk V (2001) 5 -Bis-pyrenylated oligonucleotides displaying excimer fluorescence provide sensitive probes of RNA sequence and structure. Nucleic Acids Res 29 3611-3620... 

Paris PL, Langenhan JM, Kool ET (1998) Probing DNA sequences in solution with a monomer-excimer fluorescence color change. Nucleic Acids Res 26 3789-3793... 

Lewis FD, Zhang Y, Letsinger RL (1997) Bispyrenyl excimer fluorescence a sensitive oligonucleotide probe. J Am Chem Soc 119 5451-5452... 

Zhen Z, Tug C-H (1991) Hydrophobic effects on photophysical and photochemical processes excimer fluorescence and aggregate formation of long-chain alkyl 4-(N, N-dimethy-lamino ) benzoate in water-organic binary mixtures. Chem Phys Lett 180(3) 211—215... 

Lehrer, S. S. (1997). Intramolecular pyrene excimer fluorescence A probe of proximity and protein conformational change. Fluorescence Spectroscopy 278, 286-295. 

There is experimental evidence that triplet states indeed play an important role in radical ion reactions. The formation of excimers has been suggested on the basis of chemiluminescence emission spectra, e.g. in the case of N-phenylcarbazole 15> and in some other experiments 18>. Other authors 19>20> have observed that the excimer fluorescence reported is probably produced by decomposition products of the radical ions or other impurities, as is very probably the so-called preannihilation chemiluminescence which occurs in electrogenerated chemiluminescence (see 21>). 

Fluorescence Measurement Fluorescence spectra were measured on a Spex Fluorolog 212 spectrofluorometer equipped with a 450 W xenon arc lamp and a Spex DM1B data acquisition station. Spectra were recorded in the front-face illumination mode using 343 nm as the excitation wavelength. Single scans were performed using a slit width of 1.0 mm. PDA fluorescence emission spectra were recorded from 360 to 600 nm, with the monomer and excimer fluorescence measured at 376.5 and 485 nm, respectively. Monomer and excimer peak heights were used in the calculation of the ratio of excimer to monomer emission intensities (Ie/Im). Excitation spectra were recorded from 300 nm to 360 nm and monitored at 376.5 and 500 nm for the monomer and excimer excitation, respectively. 

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

In a film, however, molecular mobility is severely limited, so that excimer fluorescence must arise mainly from pairs or groups of pyrene molecules that were approximately in the excimer configuration when the film was cast. Thus, the intensity of the excimer emission is also an indication of the local concentration of pyrene in the cast film. If the pyrene aggregates, we expect that the excimer fluorescence would increase with aggregation. This system can be used to look at the aggregation of very low concentrations of a small molecule dye in a polymer film, and potentially detect molecular aggregation before it would be observable by other tech-... 

Barnes RL, Birks JB (1966) Excimer fluorescence. X. Spectral studies of 9-methyl and 9,10-dimethyl anthracene. Proc R Soc A Math Phys Eng Sci 291 570-582... 

Box 8.2 Intramolecular excimer fluorescence for probing the mobility of bulk polymers... 

Figure B8.2.1 shows the fluorescence spectra of DIPHANT in a polybutadiene matrix. The h/lu ratios turned out to be significantly lower than in solution, which means that the internal rotation of the probe is restricted in such a relatively rigid polymer matrix. The fluorescence intensity of the monomer is approximately constant at temperatures ranging from —100 to —20 °C, which indicates that the probe motions are hindered, and then decreases with a concomitant increase in the excimer fluorescence. The onset of probe mobility, detected by the start of the decrease in the monomer intensity and lifetime occurs at about —20 °C, i.e. well above the low-frequency static reference temperature Tg (glass transition temperature) of the polybutadiene sample, which is —91 °C (measured at 1 Hz). This temperature shift shows the strong dependence of the apparent polymer flexibility on the characteristic frequency of the experimental technique. This frequency is the reciprocal of the monomer excited-state...

Bokobza L. and Monnerie L. (1986) Excimer Fluorescence as a Probe of Mobility in Polymer Melts, in Winnik M. A. (Ed.), Photophysical and Photochemical Tools in Polymer Science, D. Reidel Publishing Company, Dordrecht, pp. 449-66. 

Georgescauld D., Desmasez J. P., Lapouyade R., Babeau A., Richard H. and Winnik M. (1980) Intramolecular Excimer Fluorescence A New Probe of Phase Transitions in Synthetic Phospholipid Membranes, Photochem. Photobiol. 31, 539-545. 

When a fluoroionophore contains two fluorophores whose mutual distance is affected by cation complexation, recognition of this cation can be monitored by the monomer/excimer fluorescence-intensity ratio (see Chapter 4, Section 4.4.1 for ex-rimer formation). Cation binding may favor or hinder exrimer formation. In any case, such a ratiometric method allowing self-calibration measurement is of great interest for practical applications. 

Attribution and characteristics PEN excimer fluorescence PEN monomer phosphorescence Emission peaking at 618nm, with a shoulder at 690 nm... 

L. Bokobza, C. Pham-Van-Cang, L. Monnerie, J. Vandendriessche, and F. C. De Schryver, Investigation of the mobility of polybutadienes 1. Excimer fluorescence technique, Polymer 30,45 (1989). 

L. Bokobza L, E. Pajot-Augy, L. Monnerie, A. Castallan, and H. Bouas-Laurent, Excimer fluorescence as a probe of mobility in bulk polymers, Polymer Pholochem. 5, 191 (1984). 

Lateral diffusion of phospholipids in model membranes at ambient pressure has been studied over the years by a variety of techniques including fluorescence recovery after photobleaching (FRAP), spin-label ESR, pulse field gradient NMR (PFG-NMR), quasielastic neutron scattering (QENS), excimer fluorescence and others.In general, the values reported for the lateral diffusion coefficient (D) range from 10 to 10 cm /s in the... 

An alternative mechanism for the formation of a two hosts-two guests complex has been suggested. From equilibrium studies of the concentration-dependence of the absorption spectra and excimer fluorescence intensities of naphthalene in the presence of beta cyclodextrin, Hamai ° concluded that the excimer fluorescence is due to a two hosts-two guests complex, formed by the association of two 1 1 beta cyclodextrin-naphthalene complexes. Thus, the mechanism can be described as follows. 

Modification of PAA/Au grafts with the amine and alcohol functionalized pyrenes 2 and 3 produced highly fluorescent films [23]. These deriva-tized films exhibited both monomer and excimer fluorescence. The relative amounts of monomer and excimer emission depended on the pyrene concentration used in the derivatization process. When modest concentrations... 

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