Polystyrene film emission spectra

Figure 10-8. Emission spectra of a free standing film of a blend system consisting of 0.9% MEH-PPV in polystyrene with ca. I011 cm 3 TiOj-particlcs. The nanoparlicles act as optical scattering centers. The emission spectrum is depicted for two different excitation pulse energies. Optical excitation was accomplished with laser pulses of duration I Ons and wavelength 532 nm (according to Ref. 171).

Figure 10.12—Sequence of events necessary to obtain a pseudo-double beam spectrum with a Fourier transform IR spectrometer. The instrument records and stores in its memory two spectra representing the variation of lu (blank) and / (sample) as a function of wavenumber (emission spectra 1 and 2 above). Then, it calculates the conventional spectrum, which is identical to that obtained on a double beam instrument, by calculating the ratio T — /// — f(A) for each wavenumber. Atmospheric absorption (CO2 and H20) is thus eliminated. The figure illustrates the spectrum of a polystyrene film.

Fig. 9. The emission spectrum from a polystyrene resist film (0.5 pm thick) excited by 2.5 MeV He+. The vertical axis was not calibrated for the efficiency of the optical system and the detector. This spectrum was not influenced by the quenching seen in Fig. 6...

In Figure I we compare emission spectra for polystyrene in dilute solution and as a solid film, and for a model monomer, ethylbenzene, in dilute solution. Polystyrene in solution exhibits, in addition to a monomer-like emission, a broad excimer emission maximizing at emission spectrum is not unique to high molecular weight polymer. Indeed, 1,3-diphenylpropane exhibits (la,8) very similar total emission spectra. The excimer emission lifetime is (4) 12.5 ns in CH2CI2 at room temperature, while monomer-like emission decay and excimer emission rise times are reported (2) to be of the order of a nanosecond in cyclohexane solution. 

Figure 10.9 Sequence for obtaining a pseudo-double beam spectrum with a Fourier transform infrared spectrometer. The apparatus records and memorizes two spectra, which represent the variations of 7q (the blank) and I (sample) as a function of the wavenumber (these are emission spectra 1 and 2). Next the conventional spectrum is calculated, identical to that of an instrument of the double beam type, by calculating the ratio T = 1/4 = fW for each wavenumber. Strong atmospheric absorption (COj and HjO), which is present along the optical path is eliminated in this way. The illustrations correspond to the spectrum of a polystyrene film.

It has been shown [155,171] that the dependence of excimer emission intensity on acceptor concentration obeys the Stern—Volmer equation whether M or D is the donor, whereas a second-order equation is obtained if both types of excited state simultaneously act as donor. It seems that in poly-1-vinylnaphthalene and polyacenaphthalene films at room temperature, energy transfer to benzophenone occurs from M, although normal fluorescence cannot be detected in the emission spectrum of the polymers in these conditions [155]. Decay time measurements have shown that the excimers in solid polyvinylcarbazole are traps rather than intermediates in the energy transfer process [148]. With polystyrene, however, it has been clearly demonstrated that energy transfer to tetraphenylbutadiene occurs from both excimer and isolated excited chromophore [171]. 

Fluorescence spectra from a polystyrene film photolyzed in vacuum are shown in Figure 2. Similar but less intense spectra were observed in films irradiated in air. The Product I responsible for this spectrum was partially extractable from the film with methanol the fluorescence spectrum of the extract is shown also in Figure 2. Comparison of these spectra with those of a wide variety of reasonable model compounds suggests that Product I is related to 1,3-diphenyl-l,3-butadiene since the spectral match with 1,4-diphenyl-l,3-butadiene, shown in Figure 2, is quite close. Product I spectra were obtained also from the residual films after extraction, indicating that the diene moiety may form part of a photolyzed chain as well as exist as a short-chain fragment. Fluorescence spectra that could be related to higher polyenes were not detected in the vacuum exposures. In air exposures, however, the prompt emission spectra from films did exhibit a weak shoulder superimposed on the... 

A spectral shift due to interconversion between monomer and excimer/exciplex emission can be exploited to develop temperature sensors for the macroscopic environment. For example, a thermochromic sensor film was developed by immobilising perylene in a polystyrene film with iV-aUyl-iV-methylaniline (NA) [41]. In solution and in the absence of NA, perylene emits blue fluorescence — 475 nm). In thin films and in the presence of NA, an additional broad red emission band is observed (Aem = 551 nm), which is attributed to the perylene-NA exciplex. The fluorescence spectrum is temperature dependent on heating between 25 and 85 °C the relative intensity of the blue monomer emission increases at the expense of the exciplex emission band, indicating that at higher temperatures the monomer-exciplex equilibrium is shifted in favour of the monomer. A wavelength ratiometric approach based on the relative intensities of the two emission peaks as a function of temperature was used to calibrate the sensor film [41]. 

Figure 15.8 Emission spectra of a polystyrene film at 30°C. (a) Spectrum before the correction for the emission from the trapping blackbody and (b) spectrum after the correction for the emission from the trapping blackbody. See text for details.

For the distyrylbenzene carbon-centered tetramer 46b, the fluorescence spectrum in the solid him differs from the spectra in solution or in a polymer matrix due to excimer formation [93]. A concentration of 5% in a polystyrene matrix is sufficient for a distinct broadening of the emission. For the higher homologue 46c, a fluorescence maximum of 472 nm was measured in freshly prepared films. If the film is thermally annealed, the spectrum shifts to 511 nm, probably due to intermolecular arrangement that favors excimer formation. 

---