Monomeric encapsulation of phthalocyanine-dye molecules in the pores of Si-MCM-41 and Ti-MCM-41

Titanium species and substituted or unsubstituted zinc phthalocyanine (ZnPc ) complexes exhibiting negative, positive or no charges are incorporated in mesoporous MCM-41 materials by (i) hydrothermal synthesis in the presence of hexadecyltrimethylammonium chloride as surfactant and (ii) impregnation of pre-synthesized calcined Si-MCM-41. The ordering of the hexagonal MCM-41 structures is revealed from X-ray diff ractograms and nitrogen adsorption isotherms. The dispersion and the coordi nation of the Ti in the walls or in the pores is deduced from UV/Vis diffus e reflectance spectra (DR-UV/Vis). The amount of Ti built into the walls of the MCM-41 under maintenance of a perfect hexagonal structure is restricte d to about 2 wt.%. In the pores up to 8 wt.% Ti can be fixed a silanol grou ps under molecular, i.e. non-aggregated, dispersion. The degree of dispersion of ZnPc is concluded from the analysis of the Q-ba nd structure in the DR-UV/Vis spectra. Predominantly non-aggregated ZnPcs i n a monomeric state can be obtained, (i) if the ZnPC is incorporated in the micellar structure of the surfactant molecules by adding it to the synthes is gel of the MCM-41 or (ii) if the ZnPc is adsorbed to Ti-MCM-41 with Ti s pecies in high dispersion in the pores. A tight contact between the donor Z nPc and the acceptor titanium oxide, enables an electron transfer and a que nching of the fluorescence of the dye.