Emission spectra copolymers

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. 

On the other hand, the exposed copolymer yarn containing 4.0 mole percent 4,4 -BPDC still exhibits the normal terephthalate fluorescence (388 nm emission) as the major band in the emission spectrum when excited with 342 nm energy. 

TGA, iodometric, mid-IR, luminescence (fluorescence and phosphorescence) and colour formation (yellowness index according to standard method ASTM 1925) were all employed in a study of aspects of the thermal degradation of EVA copolymers [67], Figure 23 compares a set of spectra from the luminescence analysis reported in this work. In the initial spectra (Figure 23(a)) of the EVA copolymer, two excitation maxima at 237 and 283 nm are observed, which both give rise to one emission spectrum with a maximum at 366 nm weak shoulders... 

A polymer containing anthracene, [Ru(bpy)3]2 , and [Os(bpy)3]2+ [all covalently linked to a 1 1 copolymer of styrene and m,p-(chlorome-thyl)styrene] has been prepared, and its emission spectrum and intramolecular electron-transfer properties have been studied (569). 

On the other hand, the excimer emission because it is 80% non-correlated with monomer trap emission and because it is effectively quenched in the copolymers even at low temperatures, must largely arise from a mobile precursor. The activation energy for hopping of this precursor is implied to be <10 cm l. This is not unreasonably low(12,17), and indeed, the zero-point energy of the phenyl chromo-phore could in principle allow completely activationless hopping (tunneling) at reasonable rates. Determination of the true situation will require measurements at still lower temperatures, which are now in progress. We note that the polystyrene emission spectrum at 4.2K reported in (Id) indicates a monomer/excitner intensity ratio nearly the same as our 20K spectra. 

PL and EL emissions from a very low band-gap copolymer 330 (Eg 1.27eV) was demonstrated by Swedish researchers [411]. The material has two absorption peaks at 400 and 780 nm and emits light in the NIR region. The PL spectrum of thin films has one peak at 1035 nm, which is blue-shifted by ca. 60 nm on annealing at 200°C for 10min. The ITO/PEDOT/330/Ca/Al diode was positively biased when the Al/Ca electrode was connected to lower potential and the EL emission became observable at 1.1 V (AEL = 970 nm). The d>KLfor a nonoptimized device was quite low (0.03-0.05%), nevertheless demonstration of EL from PLED in the NIR can be important for communication and sensor technologies (Chart 2.85). 

The pure-film spectra of the alternating copolymers have been reported only for P(S-fl/t-MMA) and P(2VN-a//-MMA)5S>. For the former polymer, a fluorescence band similar to toluene was observed, distinguished only by a slight broadening at X > 290 nm. The P(2VN-a//-MMA) film spectrum was described as having a maximum at 365 nm, with appreciable fluorescence intensity at 425 nm. This emission, which could not be positively identified as excimer fluorescence, was attributed to an impurity by Fox et al.55). If the results for P(S-a//-MMA) are representative of all the copolymer film spectra, they indicate that very few intermolecular EFS are formed. 

In a revealing experiment, Toyoda and Fujiki showed that the UV absorption and emission spectra of (PhMeSi) are virtually identical to those of the copolymer, (PhMeSi)o.95 [PhSiCH2C (H)(CH3)CH2CH3]005 . The latter is known to be helical in solution from its CD spectrum. The implication is that (PhMeSi) , which was for many years described in terms of the anti-gauche model, is actually helical in solution also.69 The evidence which is accumulating now suggests that nearly all polysilanes adopt helical conformations in solution. 

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