Fluorescence of Adsorbed Aromatic Hydrocarbons. Molecular and Donor-Acceptor Interactions with the Surfaces of Al₂O₃, Ga₂O₃ and TiO₂

Nature and Estimation of Functional Groups on Solid Surfaces

“…n-donor molecules interact with Lewis acid sites on oxide surfaces and may form electron-donor-acceptor (EOA) complexes. As shown by Oelkrug and Radjaipour [358] these EOA complexes can give rise to luminescence spectra. Examples are shown in Figure 32 of the excitation and emission spectra of anthracene adsorbed on y-A1 2 0 3 and {3-Ga 2 0 3 • The absorption spectra are similar to those of the uncomplexed anthracene molecule in that the number of bands is identical.…”

“…Fluorescence spectra of chemisorbed aromatic hydrocarbons could therefore be expected to probe the Lewis acidity of oxide surfaces. However, the order of the transition energies of the fluorescence maxima of chemisorbed anthracene on the surfaces of y-AI 2 0 3 , /3-Ga 2 0 3 and Ti0 2 (anatase) is contrary to the order which would follow from the Lewis acidity of the surfaces [358]. This may be due to other factors than only the electron affinity EA influencing the fluorescence transition energy.…”

“…32 b) were due to the EOA complexes, since the transition energies of a variety of n-donor molecules adsorbed on y-A1 2 0 3 followed the approximate equation or Mulliken's charge transfer theory [358,359]. ID in the above equation is the ionization potential of the donor molecule, EA the electron affinity of the acceptor surface and C a constant which depends on the donor-acceptor distance.…”

Physical Aspects of Radiation-Induced Processes on SiO2, γ-Al2O3, Zeolites, and Clays

“…As given in Table , heating γ-Al 2 O 3 increases the extent of surface CT sites. This effect is readily seen by studies of the photophysics of adsorbed arenes on γ-Al 2 O 3 . − As in the SiO 2 system, a probe molecule of established photophysics is adsorbed onto γ-Al 2 O 3 , and the resulting spectroscopy is used to interpret the surface.…”

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7 Energies of the CT bands of various aromatic hydrocarbons adsorbed on γ-Al 2 O 3 versus the ionization potential of the hydrocarbons: (A) maximum of the absorption band, ν A ; (Β) Ο−Ο (ν A + ν F )/2; (C) maximum of the fluorescence by ν F . Reprinted with permission from ref . Copyright 1980 Z. Phys.

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