Phosphorescence polystyrene

Figure 1. Logarithm of the phosphorescence intensity IT as a function of reciprocal temperature for films of (a) polyethylene and (b) polystyrene containing traces of carbonyl groups.

Electron transfer kinetics from the triplet excited state of TMPD to PA in polystyrene has been monitored by phosphorescence emission decay in ref. 85. The rate constant has been found to be invariant over the temperature interval 77-143 K. Parameters ae and ve calculated from the phosphorescence decay using eqn. (12) were found to be ae = 3.46 A and vc = 104 s 1. 

Figure 19.4 (A) Extinction spectra of silver nanoparticle films used for PtOEP emission enhancement. (B) Corresponding excitaticm spectra monitored at 650 mm of 6 nm films of PtOEP in a polystyrene binder spin cast onto the silver films. (C) Excited state decay dynamics of the PtOEP phosphorescence for 6 nm films excited by S ns pulses at 332 nm with no silver (c) and on substrates like number 4 from A with silver coverage to optimize enhancement (b). The instrument resolution when detecting scattering of the excitation pulse (a) is shown for reference. Reprinted from reference 43 with permission of the American Chemical Society.

A similar temperature dependence of the decay profile was also observed for benzophenone phosphorescence in other acrylic polymers (28) and in polystyrene (PS) and polycarbonate (PC) (29). 

Figure 3. Tanperature dependence of reciprocal lifetime, 1/T, (O, A) and contribution of non-exponential term, B, (, A) for benzophenone phosphorescence in PMMA (O ) and in polystyrene...

Weak delayed-emission spectra of vacuum- or air-irradiated copolymer films were similar in intensity and showed a phosphorescence maximum at 432 nm with shoulders ca. 390 nm and 450 nm on excitation at 260 nm in addition to a very weak maximum at 505 nm excited at 380 nm. These spectra are close to those shown in Figure 4 for ketone phosphorescence in photooxidized polystyrene and agree reasonably well with phosphorescence spectra for model napthaleneones (15). Energetically, the quench-... 

The modulation technique mentioned above has been used to identify triplet excimers in 1,2-benzanthracene and 1,2 3,4-dibenzanthracene at high solute concentrations167 and the differences between luminescence from naphthalene in fluid solution in the temperature range 353—173 and naphthalene in a rigid solution at 77 have been ascribed to phosphorescence from a triplet excimer.168 Excimer formation in solid poly-(2-vinylnaphthalene) and polystyrene is found to be dependent on the temperature at which the film is cast, and a statistical model based on the rotational isomeric state approximation has been used to formulate an expression for the fraction of excimer sites in the solid systems.168 Kinetic equations for dimer formation and decay, based on the statistical mechanics of ideal gases, have been obtained. These equations, derived from the N-atom von Neumann equation, take into account both bimolecular and termolecular equations.157 158 160... 

Figure 3 The corrected excitation spectrum of polystyrene phosphorescence compared with the action spectrum of photodegradation. The extent of degradation is given by AO.D., the change in sample optical density at 400 nm (Reproduced by permission from J. Appl. Polymer Sci., 1974, 18, 419)...

In contrast, when 1% poly( 1-vinylnaphthalene) is blended with 99% polystyrene, the result is mainly polystyrene phosphorescence. These results lend themselves to the conclusion that energy migration must occur intramolecularly via the mani-... 

The ketone group is a useful model because it can be excited selectively in the presence of other groups commonly contained in polymer chains, such as the phenyl rings in polystyrene, and so the locus of excitation is well defined. Furthermore, there is a great deal known about the photochemistry of aromatic and aliphatic ketones, and one can draw on this body of information in interpreting the results. A further advantage of the ketone chromophore is that it exhibits a number of photochemical processes from the same excited state. Thus one has a probe of die effects of the polymer matrix on these processes by determination of the quantum yields. The competing processes include (1) fluorescence (Eq. 26), (2) phosphorescence (Eq. 27), (3) the Norrish type-I reaction (Eq. 28), (4) the Norrish type-II reaction (Eq. 29), (5) photoreduction (Eq. 30), (6) the... 

FIGURE 7. Phosphorescence decay and oxygen-induced fluorescence of chrysene ( v-10-2 M) in polystyrene fluffs. The upper trace is the oxygen-induced fluorescence (sum of processes 44-46) and also shows the very weak triplet-triplet annihilation fluorescence decay starting on the left. The lower trace is the phosphorescence, recorded simultaneously at 500 nm. The oxygen was admitted at approximately 90 msec [reprinted, with permission, from R. D. Kenner and A. U. Khan, Chem. Phys. Lett., 643 (1975)]. 

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