Fluorescence dodecane

Although pure biphenyl does not fluoresce, an intense blue phosphorescence is emitted from a crystal of it as 6°K after the addition of dibenzothiophene. This phosphorescence originates from energytrapping centers created in the crystalline lattice adjacent to a dibenzothiophene molecule. The phosphorescence lifetime of a crystal of cyclo-dodecane similarly treated has also been measured. ... 

The fluorescence of liquid alkanes is supposed to originate entirely from the relaxed Si state. Walter and Lipsky [154], by measuring the fluorescence yields of alkane solutions irradiated with 165 nm photons or Kr beta particles ( niax = 0-67 MeV) relative to benzene fluorescence, determined the following yields 2.3-dimethylbutane G Si) < 1.3, cyclohexane 1.4-1.7, methylcyclohexane 1.9-2.2, dodecane 3.3-3.9, hexadecane 3.3-3.9, d5-decalin 3.4, and bicyclohexyl 3.5. After reinvestigating the intrinsic quantum yield of cyclohexane fluorescence, Choi et al. published G(5 i) = 1.45 for this alkane in Ref. 155. For tra 5-decalin a G Si) value of 2.8-3.1 has been accepted [65,128,132]. The uncertainties in the values reflect the uncertainties in the intrinsic fluorescence quantum yields. 

Very recently. LET effects on fluorescence lifetimes of low molecular polyethylene model compounds (n-alkane) have been studied by many kinds of pulse radiolysis - methods such as electron beam, ion beam and synchrotron radiation (SR) [40] pulse radiolysis techniques [41]. Figure 10 shows time profiles of the fluorescence from neat n-dodecane liquids irradiated many kinds of radiation with different LET. The fluorescence lifetimes from irradiated neat... 

Table 1. Lifetimes of the fluorescence of neat n-dodecane liquids irradiated by 28 MeV electron beam, synchrotron radiation (SR) and ion beams...

A demonstration of the single molecule detection at the liquid-liquid interface was reported for the fluorescent probe of l,l/-dioctadecyl-3,3,3/,. 3 -tetramethyI i ndoearboeyan i ne (Dil), which is a monovalent cation with two Cig alkyl chains. Thus, it has high adsorptivity at the dodecane-water interface. 

Aqueous phase (2.7 mm3) was placed in the thin lower compartment of the microcell and the Dil dodecane solution (63 mm3) was added on top of the aqueous layer. Fluorescence of the interfacial Dil was observed in the range of 571-575 nm. The influence of two kinds of surfactants, sodium dodecyl sulfate (SDS) and dimyristoyl phosphatidylcholine (DMPC), on the lateral diffusion dynamics of single molecules at the interface was investigated. DMPC was dissolved in chloroform, and the solution was mixed with pure diethyl ether at a ratio of 1 19 (chloroform diethyl ether) by volume. Pure water was placed in the lower container, and the DMPC solution was subsequently (5 mm3) spread carefully on the water. After evaporation of chloroform and diethyl ether, the Dil dodecane solution was added on the DMPC layer. Since Dil has a high... 

Fig. 13. Single molecule detection of Dil at the dodecane-water interface by fluorescence microscopy (left). Short photon burst in the SDS systems and (right) long burst in the DMPC systems.

FIGURE 10.5. The left figure shows the schematic illustration of laser-induced fluorescence microscopy under the total internal reflection for the detection of single Dil molecules at the dodecane-water interface. Abbreviations ND, ND filter XJ2, kl2 plate M, mirror L, lens C, microcell containing dodecane and aqueous phases O, objective (60 x ) F, bandpath filter P, pinhole APD, avalanche photodiode detector. The right portion of the figure shows the composition of the tnicrocell. 

Time resolved spectroscopy has developed assignments of intermediate species in radiation chemistry as revealed in the other sections. However, because solid polymers are less transparent, the works obtained so far seem to be limited mainly to polymer solution systems or liquid model-compounds. The lifetime of intermediates depends on LET the fluorescence lifetime of n-dodecane is shorter for higher LET radiation [83], which was studied as liquid model compounds for polyethylene. The observation is attributed to scavenging upon encountering of intermediates. Light emission from excimers of solid polystyrene has constant lifetime irrespective to LET [84], whereas polystyrene... 

Functionalization of nanorods with polyelectrolytes has been carried out by layer-by-layer deposition (92). First, CTAB-coated nanorods are prepared. Since these nanorods are positively charged, they can adsorb cationic and anionic poly electrolytes. Functionalization of nanorods with dyes is possible a fluorescent dye, 4-chloro-7-nitrobenzofurazan has been functionalized on the surface of Ti02 nanorods (93). Functionalization with a photoactive molecule such as ruthenium(II) tris(bipyridine) is also possible (94). A thiol derivative of the bipyridyl complex (Ru(bpy)3+-Cs-SH) in dodecane thiol is used for the functionalization of gold nanorods. Functionalization of block magnetic nanorods is very useful (95), for example, in the separation of proteins. Consider a triblock nanorod consisting of only two metals, Ni and Au. If the Au blocks are functionalized with a thiol (e.g. 11-amino-1 undecane thiol) followed by covalent attachment of nitrostreptavidin, then one can... 

In the above reaction scheme Solv" ", C-RH+, S represent the solvent cation, cyclohexane cation and hexafluorobenzene (HFB) anion respectively. The spin-dynamics of S and c-RH+ determine the magnetic field effect, since the spin wave-function for the ion pair (S / c-RH+) evolves differently at the different magnetic field strengths. The intensity of recombination fluorescence of the solution is determined by the rate of radiative deactivation of S [reaction (7)], which is accumulated within the simulation program. Although this model is not a complete description of the radiolysis of n-hexane which contains a solution of HFB and cyclohexane, it does however, take into account the most important aspect of the proposed relaxation mechanism, namely cross recombination. A more detailed reaction scheme for the radiolysis of n-dodecane is considered later in this chapter (in Sect. 8.6), which takes into account the excited state chemistry as well as spin-exchange reactions. 

The second reaction scheme investigated (shown in Tables 8.10 and 8.11) as part of this work is much more exhaustive and takes into account the excited state and neutral radical chemistry, which can both influence the fluorescence rate. The model includes radical cations of the solvent (S ) and of the electron donor (D+), electrons (e ) and excited states of the solvent and the solute ( D ). The diffusion coefficient of all the species involved in the reaction scheme are shown in Table 8.9. These parameters are typical for the well studied chemical system tetramethyl-p-phenylenediamine solutions in n-dodecane [30-33]. 

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