Polymer luminescence spectra

Polymer Luminescence Spectra. Figure 1 shows typical fluorescence and phosphorescence excitation and emission spectra obtained from commercial polypropylene film (or powder). Poly(4-methylpent-l-ene) exhibits similar spectra to those of polypropylene. The excitation spectrum for the fluorescence has two distinct maxima at 230 and 285 nm while that of the phosphorescence has only one distinct maximum at 270 nm with rather weak and diffuse structure above 300 nm. It is clear from these results that the fluorescent and phosphorescent chromophoric species cannot be the same. This, of course, does not rule out the fact that both may arise from carbonyl emitting species, as will be shown later, since these chromophoric groups when linked to ethylenic unsaturation can have quite distinct absorption (14) and emission spectra (15,16,17). 

The powerful role of the exitonic migration was proved on the basis of the luminescence and photosensitivity investigations [270]. The preliminary ultraviolet illumination of PAC increases the photosensitivity and decreases the luminescence. The experimental data are given in Fig. 40. One can see the redistribution of the maxima intensity in the spectra without changing their positions. Apparently ultra violet illumination promotes the photolysis of the weak coordination bonds. This leads to the changing of the polymer homolog content. Stimulated exciton dissociation on the ruptured bonds results in an increase in the photosensitivity and a luminescence decrease. The experiments carried out at 77 K show that in the luminescence spectrum of irradiated frozen PAC a new maximum appears with a position close to the phosphorescence maximum of diphenylbutadiene. So the rupture of weak coordination bonds under ultraviolet irradiation was proved. 

Figure 13.36 Upconversion luminescence spectrum of the Y Er-Yb co-doped coordination polymer [(Y Er-Yb)(oba)(ox)o.5(H20)2]n [113]. (Reproduced from Inorganica Chimica Acta, 362, C. Y. Sun et al., Assembly and upconversion luminescence of lanthanide-organic frameworks with mixed acid hgands, 325-330, 2009, with permission from Elsevier.)...

Intermediates in the radiation chemistry of high polymers include ions and trapped electrons, radicals and excited states. Free radicals trapped after irradiation have been studied mainly by electron spin resonance (ESR) and in some cases by chemical methods and by ultraviolet or infrared spectroscopy. The detection of free radicals during radiolysis has been performed by pulse radiolysis and also by ESR. Trapped ions and radical-ions were characterized by absorption spectroscopy and thermoluminescence while pulse radiolysis allows their detection during irradiation. Excited states, owing to their very short lifetime, could be observed only by pulse radiolysis or by the measurement of the luminescence spectrum and decay time during steady irradiation. 

The second more common case is represented by a blend in which the two polymers are not miscible. The resulting heterogeneous system will yield a luminescence spectrum different from that of a miscible blend. This can be rationalized using Figure 2 which is a schematic of a region near the interface between domains of the phase-separated blend com-... 

One advantage of polymers which is especially useful for laser-oriented applications is the red shift in the luminescence spectrum in comparison with their absorption. This phenomenon gives the opportunity of light amplification without losses caused by self-absorption in active media. Many efforts are now being concentrated on the manufacture of electronically pumped polymer lasers, although they have not yet met with success. 

Photophysical Processes in Pol,y(ethy1eneterephthalate-co-4,4 -biphenyldicarboxyl ate) (PET-co-4,4 -BPDC). The absorption and luminescence properties of PET are summarized above. At room temperature the absorption spectrum of PET-co-4,4 -BPDC copolymers, with concentrations of 4,4 -BPDC ranging from 0.5 -5.0 mole percent, showed UV absorption spectra similar to that of PET in HFIP. The corrected fluorescence spectra of the copolymers in HFIP exhibited excitation maxima at 255 and 290 nm. The emission spectrum displayed emission from the terephthalate portion of the polymer, when excited by 255 nm radiation, and emission from the 4,4 -biphenyldicarboxylate portion of the polymer when excited with 290 nm radiation. 

Both polymers 18 and 20 are luminescent in the solid state. In the case of compound 18, the shape of the emission spectrum depends from excitation wavelength. Upon excitation at 320 nm, a broad featureless emission is observed at 530 nm. After excitation at 380 nm, the emission spectrum exhibits a sharp maximum at 429 and a broad hump centered at 520 nm (Fig. 36). Three maxima at 422, 505, and 542 nm are found in the emission spectrum of [(CuI)2 p-o-TolS(CH2)4STol-o 2]ra 20 (Fig. 37b) after excitation at 360 nm. The resemblance of the band at 422 nm with the emission band of solid l,4-bis(o-tolylthio)butane (Figure 37b) indicates that this emission is essentially... 

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