Photoactive Self-Standing Films Made of Layered Double Hydroxides with Arranged Porphyrin Molecules

Abstract

Transparent films of layered double hydroxides (LDH) have been prepared by the deposition of their chloroform dispersions. The advantage of this method is the potential to obtain large and transparent self-standing films, composed of highly ordered LDH platelets, with durability that allows further modifications by anion exchange. The LDH interlayer can be filled with anionic porphyrins that impose interesting photophysical and photochemical properties on the films. Intercalated porphyrins, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and its palladium complex (PdTPPS), exhibit luminescence emission. The triplet state dynamics in the absence of oxygen are not affected by the LDH matrix, whereas the interaction of the triplet states with oxygen to produce singlet oxygen, O2(1Δg), is less effective in the film than in solution. High local concentrations of O2(1Δg) and of the triplet states within the films induce singlet oxygen-sensitized delayed fluorescence (SODF). This work is the first report on LDH-based materials capable of emitting SODF. The detailed kinetic analysis of SODF behavior indicates a short singlet oxygen lifetime of ∼0.3 μs, probably due to the close proximity of hydroxide groups at the LDH layers.