Poly fluorescence spectra

Fig. 8 Absorption (left) and fluorescence (right) spectra of 10 5 M Cyan 3iPr in buffer (dashed) and of 3 x 10-5 M Cyan 3iPr in presence of 3.5 x 10 5 M b.p. poly(dA)-poly(dT) (solid lines). Free dye fluorescence spectrum intensity is multiplied ten times [40]...

The close correspondence of the DNA absorption spectrum with that of a mixture of mononucleotides of the same composition illustrates the weak nature of the interactions between neighboring purine and pyrimidine bases guanine (G), cytosine (C), adenine (A), and thymine (T) at an interplanar separation of 3.36 A in the unexcited double-helical configuration. On the other hand the structureless fluorescence band of (calf-thymus) DNA is red-shifted by 3500 cm-1 from the fluorescence spectral origin of the mononucleotides it closely resembles the fluorescence spectrum of the dinocleotide ApT (and of poly dAT) and is accordingly identified131 with the fluorescence... 

The third group ofpolychromophoric compounds to be discussed are homopolymers in which the pendant rings are separated from the backbone by one or more atoms. The polymers of allyl arenes, which lack only the n = 3 ring spacing of aryl vinyl polymers, have been studied very little. The fluorescence spectrum of poly(l-allyl-naphthalene) in dilute dichloromethane solution has been reported 28). Like 1-ethyl-naphthalene, the maximum intensity was seen at 337 nm, but a weak, broad shoulder was also recorded for the polymer at 410 nm. The fluorescence ratio Iu/IM for poly(l-allylnaphthalene) was only 1/100 th the value for P1VN 28). The excimeric nature of the 410 nm emission in the allyl-based polymer has not been confirmed, since neither the lifetime nor the excitation spectrum of this fluorescence band are known. 

Polyfluorene was first synthesized by Fukuda et al. via oxidative polymerization of huorene monomers using ferric chloride as a catalyst.2,11 Both mono- and dialkyl-substituted polyfluorenes were synthesized. Figure 10.1 shows the repeat unit of poly(9,9/-dialkyl-huorene-2,7-diyl). The polymers are soluble in common solvents such as chloroform, dichloromethane, and toluene. Figure 10.2 shows the absorption and fluorescence spectra of a solution of poly(9,9/-dihexylfluorene-2,7-diyl) (PDHF) in chloroform.11 The onset of the tt-tt absorption is at 420 nm, rising to a peak at 380 nm, yielding an optical gap of 2.95 eV. The fluorescence spectrum contains vibronic peaks at 417 and 440 nm and a shoulder at 470 480 nm. 

Figure 3. Absorption and emission spectra of poly(methylphenyl-silylene) in 2-methyltetrahydrofuran at 77 K. The fluorescence spectrum vas measured with a resolution of 0.265nm. The long wavelength emission vas measured with a resolution of 1.32nm ...

In order to proceed it is now necessary to consider the nature of the lowest excited state of these polymers. One description which appears to be particularly appropriate to these materials is that given by the molecular exciton theory (37,38). This of course is suggested by the nature of the fluorescence spectrum itself and in addition this approach has proven to be quite successful in the Interpretation of the electronic states of the alkanes, the structural analogs of the poly(organosllylenes) ( 3, 6). The basic assumption... 

We employ method B to study effects of this type. In this mode, our apparatus yields relative high-resolution fluorescence spectra at different time windows after excitation of the sample by the 355 nm pulse. The spectra are acquired by the upconversion method. The upconverted fluorescence spectrum is recorded simultaneously at all monitored wavelengths by an optical multichannel analyzer. It is constructed from a poly-chromator (HR320 Instruments SA) and an intensified silicon photodiode array detector (Princeton Applied Research Model 1412). The detector is interfaced to our Cromemco computer. 

It is known that [3.3]paracyclophane, which has the almost highest transannular interaction of the less distorted benzenes (12), has the fluorescence emission at longer wavelength (356 nm) (18) than the excimer of 1,3-diphenylpropane (332 nm). The fluorescence spectrum of the cyclopolymer, poly(St-C3-St), recorded under the same conditions as for [3.3]paracyclophane is illustrated in Figure 1 (20). Both have the fluorescence at the same wavelength, and therefore the polymer is supported to contain [3.3]paracyclophane units as sequence units. The fluorescence emission at 312 nm is ascribed to the residual styryl groups. 

The UV-vis electronic spectrum exhibited an intense broad absorption which started at a wavelength A < 200 nm and decreased to 460 nm (Figure 9.1). Corresponding to the electronic absorbance, an intensive, broad fluorescence peak with at 460 nm was found in the fluorescence spectrum of the polymer (Figure 9.1). Both UV-vis and fluorescence properties were consistent with the poly(phenylcarbyne) structure [20]. 

Figure 9.1 (a) UV-vis electronic spectrum (cyclohexane) and (b) fluorescence spectrum (cyclohe)ane, excitation wavelength =300 nm) of poly(phenylcarbyne) obtained by this methodology. 

Figure 2. Fluorescence spectrum of a colloidal particle composed of poly(viny] acetate) [PVAc] and poly(2 ethylhexyl methacrylate) labelled with phenanthrene in the PVAc phase, curve a. Curve b is the fluorescence spectrum of an identical unlabelled particle. Curve c is obtained by subtracting b from a. The excitation wavelength was 290 nm.

Spectroscopic Properties. The UV absorption spectrum of poly(phenylsilane) 1 contains a weak transition at 294 nm (esi-si = 2489 crn- M Figure la). The absorption band assigned as the Si(o-a ) transition occurs at 294 nm and likely contains considerable phenyl (tc-tc ) character, as suggested by energy band calculations.((55) In contrast to other substituted polysilanes of similar molecular weight, we were unable to detect fluorescence for poly(phenylsilane) at room temperature in THF. 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

The heparin and poly-L-glutamate titrations show a markedly different behavior than do the DNA titrations. As polyanion is added, the fluorescence of the an-thrylpolyamine solution decreases until a well-defined minimum is reached. A new emission at 510 nm, which we assign to the anthracene excimer of 14, increases and decreases coincidently with the titrated fluorescence minimum. Likewise, the UV spectrum of 10 fiM 14 with added heparin shows hypochromism that occurs and disappears coincidently with the fluorescence minimum and a 2-nm red shift. We have proposed template-directed excimer formation as the physical basis for these observations. In the absence of heparin, fluorescence of the unassociated probe is observed. As heparin is added, the fluorescence decreases as a result of heparin-directed interaction between probe molecules. Additional heparin permits the fluorophore population to diffuse over the length of the poly anion, thus avoiding excimer formation and yielding a net CHEF. 

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