Surface photochemistry: Ketones included within a channel type solid support, the aluminophosphate AlPO4-5

Diffuse reflectance and laser-induced techniques were used to study the inclusion of an aromatic ketone, benzophenone (BZP) and also of aryl alkyl ketones such as β-phenylpropiophenone (β-PP) and γ-phenylbutyrophenone (γ-PB) into a channel type solid powdered substrate, the aluminophosphate AlPO4-5. AlPO4-5 solid support exhibits a surprisingly hydrophilic character which was shown by a blue shift of the (n, π∗) ground state absorption band of BZP and a red shift of the (π, π∗) ground state absorption band of γ-PB, when compared with the inclusion within silicalite, a hydrophobic support. Furthermore, the phosphorescence emission of BZP within AlPO4-5 was broad and a non-structured emission band of hydrogen bonded BZP centred about 440 nm was observed in a nanosecond time scale. This emission shifts up to 470 nm and was assigned to protonated excited BZP, BZPH+*, suggesting the presence of Brönsted acid sites in the substrate. In the 7.3 Å diameter aluminophosphate’s channels, β-PP shows no room temperature phosphorescence as consequence of intramolecular quenching, while the larger γ-PB exhibits a structured phosphorescence emission peaking at 452 nm. A lifetime distribution analysis for BZP/AlPO4-5 case shows a single wide band, peaking at 630 μs. The transient absorption spectra of argon purged samples revealed, superimposed on the triplet–triplet absorption of BZP, the hydroxyl–benzophenone radical (BZPOH) absorption as the main transient species in the millisecond time scale.