In the primary process of photosynthesis, chlorophyllous pigments have been immobilized into the protein matrices, and their arrangements are regulated precisely. This indicates that the immobilization of photofunctional organic molecules into inorganic matrices instead of the proteins and the regulation of the arrangements of the pigments is the first step for the construction of artificial photoredox systems because the energy conversion was performed by pigments themselves.
Mesoporous silica and mesostructured materials have attracted many interests toward various applications such as adsorbents for relatively large molecules and nanosized reaction vessels because of its high surface area and ordered mesopores. Ordered mesopores are quite useful to control of arrangements of photofunctional organic molecules because the pore diameters are comparable to the size of these molecules. However, it is difficult to control the arrangements of these molecules precisely in the mesopores by the simple liquid-phase adsorption or solubilization.
In order to synthesize a mesostructured porphyrin-silica hybrid with ordered arrangements of porphyrin, a Cu-porphyrin derivative possessing polyethylene glycol chains (PEG-Cu-Por) was used as a template. The XRD pattern of PEG-Cu-Por-SiO₂ film had three peaks (3.9, 2.2 and 1.9 nm) attributed to a 2D-hexagonal structure. The TEM images exhibited well-defined striped and honeycomb patterns. The UV-vis absorption spectrum of the film gave split Soret bands at 411 and 431 nm. All these results indicate that porphyrin rings assembled with a slip structure to form a mesostructure, which promises a new way to construct mesostructured inorganic-organic hybrids consisting of porphyrin derivatives.