Novel solid-state luminous composites from a layered inorganic–organic monolith containing neutral porphyrins

Abstract

We have succeeded in loading a neutral zinc porphyrin derivative (ZnTPPder) into a layered inorganic–organic compound, despite the well-known difficulties associated with incorporation of neutral pigments into the interlayer spaces of layered materials. We have utilized a synthetic alkylammonium–smectite monolith (A-Sm) as the host layered inorganic–organic compounds to facilitate porphyrin loading. Alkylammonium groups are located between the layers of the phyllosilicate-analogue moieties (the inorganic moiety) bonding covalently with the inorganic moiety to form the monolith. The interlayer space of A-Sm is organophilic and swells in organic solvents. ZnTPPder was loaded into A-Sm by mixing A-Sm and solutions of ZnTPPder in organic solvents under different conditions yielding ZnTPPder/A-Sm composite films. UV–VIS measurements revealed several absorption peaks assigned to the characteristic Soret (432 nm) and Q (500–650 nm) bands of ZnTPPder for all the prepared ZnTPPder/A-Sm composite films. Fluorescence emission due to ZnTPPder was observed from all the ZnTPPder/A-Sm composite films, while a reference ZnTPPder/Sm cast film prepared from ZnTPPder and a smectite (Sm) rather than A-Sm was only weakly fluorescent. This emission behaviour suggests that ZnTPPder is intercalated in the interlayer space of A-Sm with suppression of aggregation of ZnTPPder. In contrast, ZnTPPder was hardly intercalated into the interlayer space of Sm. Thus, we have demonstrated a novel and relatively easy route for loading of neutral (uncharged) pigments into a solid-state two-dimensional nanospace, a method which might be applied to prepare novel light-harvesting systems.