Heterogeneous Ti-containing MCM-41 materials were prepared for the photocatalytic isomerization of norbornadiene to quadricyclane with the aim of replacing homogeneous sensitizers. Chemical grafting produces quantum-size TiO2 crystallites highly dispersed in the pore of MCM-41. Isomorphous substitution generates Ti species in the framework of MCM-41, but some non-framework species are formed with increasing Ti content. It is found that Ti-containing MCM-41 materials show significantly higher photocatalytic activity than bulk TiO2, and the framework Ti species are more active than the surface-dispersed species.