Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

Abstract

The electronic structure of some poly͑phenylenevinylene͒s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.

The electronic structure of polyaniline and doped phases studied by soft x-ray absorption and emission spectroscopies

“…The bands ͑peak A and part of peak B͒ are dramatically depleted in the resonant case as a result of the symmetry selection rules. 15,28 Only a very small structure of peak A remains which may be due to a small incoherent contribution ͓Ref. 29͑a,b͔͒ or related to carbon lone-pair orbital.…”

“…13,14 However, the relatively low fluorescence yield and instrumental efficiencies associated with SXE in the ultra-soft x-ray regime places considerable demands on the experimental measurements in this spectral region. 15,16 In the following section, we describe the details of the experiment ͑Sec. II͒, followed by a presentation of the results and discussion ͑Sec.…”

The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies

“…The purpose of the present work is to use X-ray emission (XE) spectroscopy to investigate the electronic structure of poly(pyridine-2,5-diyl) (PPy) which is an aza-substituted poly(p-phenylene) with a sufficiently large bandgap to allow electroluminescence in the blue wavelength region [5,6]. X-ray emission spectroscopy provides an alternative technique for studying polymers but has been quite little exploited so far in that context [15]. It provides a means of extracting the electronic structure information in terms of local contributions to the Bloch or molecular valence orbitals, since the decay from the core-hole can be described according to local dipole selection 2 rules [7,8].…”

“…An intense, synchrotron radiation (SR), excitation source is therefore required which has limited the activity in this field. In a recent work we used some poly-phenylene-vinylenes, PPV, PDPV and PMPV, to demonstrate the possibility to produce resonant and nonresonant X-ray scattering spectra of polymer compounds by means of monochromatic synchrotron radiation [15]. The spectra were sufficiently resolved to allow an analysis of the spectral features in terms of electronic structure theory, and also to analyze the salient changes between the non-resonant to resonant spectra in terms of the differences of the underlying physical processes.…”

Soft-x-ray fluorescence study of the quasi-one-dimensional Heisenberg antiferromagnet tetraphenylverdazyl

“…1͒ that give raise to a broad XPS N 1s line and therefore the depletion of peaks a and d under resonant excitation of N Ka XES can be attributed to interference effects as well. 19,20 …”