An Examination of the Role B2O3 Lewis Acid Sites in Electron Transport on Porous Vycor Glass

Abstract

Photoinduced disproportionation of Ru(bpy)?+ on porous Vycor glass occurs within a fixed array of reactants by means of a mobile, photodetached electron. The absence of emission quenching when Ru(bpy)? cation exchanges onto the glass and the band gap of SiOz, the principal constituent of the glass, preclude direct electron injection into a conduction band. Instead, conduction of the photodetached electron is thought to occur via surface conduction, where the photodetached electron populates intermediate surface acceptor sites. These are shallow energy wells from which the electron can be thermally activated, but the specific identity of the site is not presently known. One possibility is the BzO3 Lewis acid sites present in the glass, and data presented here show that selectively neutralizing these BzO3 sites with chemisorbed N H 3 changes the quantum efficiency of disproportionation. The same chemistry is shown to occur in the presence or absence of chemisorbed NH3, but a surprising increase in the quantum efficiency of R~(bpy)3~+ disproportionation in the presence of chemisorbed NH3 indicates that the B2O3 Lewis acid sites are not involved in electron transport between the immobilized ions.

Long‐Lived Photoinduced Charge Separation Inside Polarity Gradient Capsules

“…These hollow capsules were fabricated and arranged with 12 bilayer films of the type (PSS-Py/PDADMAC) 4 /(PSS-Py/PAH) 4 /(PSS-Py/PEI) 4 . This enables us to build the membrane also as a gradient material, varying the composition over nanometer distances along the surface normal.…”

“…In order to compare the difference between single-component shells and polarity-gradient shells, three sorts of hollow capsules were prepared. The first was composed of (PSS-Py/ PDADMAC) 4 ,the second composed of (PSS-Py/PAH) 4 , and the third polarity-gradient shell was composed of (PSS-Py/ PDADMAC) 4 /(PSS-Py/PAH) 4 /(PSS-Py/PEI) 4 .…”

“…Figure 1 shows the decay of Py ± and Py + in the hollow shells of (PSS-Py/PDADMAC) 4 after excitation.…”

“…The Py ± is, however, exclusively short-lived. Figure 2 shows the decay of Py ± and Py + in hollow shells of (PSS-Py/PAH) 4 . One observes both the absorption peak of the cation and the anion at the beginning i.e., time less than about 100 ns, with a comparably short lifetime.…”

“…Its longer lifetime amounts to 10 ls. In contrast to the case of hollow capsules without polarity gradients, the polarity-gradient shells (PSS-Py/PDADMAC) 4 Figure 1. Decay of the excited-state absorption in hollow capsules of (PSS-Py/PDADMAC) 4 .…”