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Abstract

Solid-state XPS spectra of selected D⁺-Ar-A^- molecular systems bearing a pyridinium, pyrylium or thiapyrylium fragment as the acceptor (A⁻) and the dialkylamino group as the common donor (D⁺) are presented and analyzed on the basis of CNDO/S-CI equivalent-core computations for model compounds. The acceptor characteristics of the pyridinium, pyrylium and thiapyrylium substituents are compared to those of the nitro group in p-nitroaniline. Clearly resolved, intense shake-up excitations (∼ 20% of the main peak intensity) are associated with N 1s donor ionization in the pyrylium and thiapyrylium derivatives, whereas heteroatomic ionization in the acceptor group yields shake-up intensities of 20–30%. Unlike the case for p-nitroaniline, however, the response of the valence electrons to ionization provides little screening of the core hole, leading to relatively intense satellites well separated from the main peaks. Also, the orbitals of interest appear sufficiently shielded due to steric factors so as to inhibit core-hole-induced intermolecular interactions. Heteroatomic binding-energy differences (ΔBE) in accordance with experiment are extracted from charge-potential calculations. Analysis of the intra- and inter-molecular contributions to the relative chemical shifts shows ΔBE to be a sensitive function of the ion/counter-ion pairing scheme.