In situ physical or covalent trapping of phthalocyanine macrocycles within porous silica networks

An effective way of trapping phthalocyanines inside porous silica has been achieved when an aqueous solution of these macrocyclic species is reacted in situ with silicon alkoxide. The resultant porous gel network can encapsulate a myriad of metal phthalocyanine molecules at relatively high concentrations and, most importantly, in a disaggregated way. By employing this method metal sulfophthalocyanines of Fe, Co, Ni, Cu, Al, Eu or Sm can be encapsulated within SiO2 xerogels. Here, the chemical entrapment of phthalocyanines inside silica gel pore networks is accomplished by the attachment of bifunctional groups to the walls of these substrates; while one of these moieties is directly linked to the macrocycle end groups, the other one is covalently bonded to the silanol groups resting on the SiO2 walls. Furthermore, when the proper concentrations of phthalocyanine species, H2O, silicon alkoxide, and HCl are reacted together, it is possible to obtain monolithic translucent silica xerogels. This latter property provides straightforward evidence of the innate fluorescence of the trapped macrocycles. The average size of the cavities encapsulating the macrocyclic molecules range from 2.0 to 3.6 nm; the precise size depends on the cation present in the complex and on the identity and position of the substituent groups at the periphery of the macrocycle. When the silica network is prepared from standard and/or organo-substituted alkoxides, the aggregation, degradation or stability of the macrocyclic species trapped in silica cavities depends on the nature of the alkyl group attached to the pore walls.

Graphical abstractThe mean cavity size of SiO2 networks depends on the cation and on the identity and position of substituent groups in the sulfophthalocyanine molecule that is therein physically or covalently trapped.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Synthesis of materials consisting of singly trapped phathalocyanine molecules in SiO2 xerogels. ► Fluorescence of silica-trapped phthalocyanines is kept by covalent bonds with the pore walls. ► Pore volume, pore size, and surface area depend on the nature of the trapped macrocycle complex. ► Advanced design of hybrid systems is possible by combining macrocycles and substituted alkoxides.