We have encapsulated Zn-II tetraphenylporphyrin ((ZnTPP)-T-II) into MCM-41 and Cu(II)AIMCM-41. Raman and UV-Vis spectroscopic investigations allow us to conclude that (ZnTPP)-T-II in MCM-41 is oxidized to a considerable extent. This is consistent with the well-known fact that the mesoporous silicate framework in MCM-41 plays the role of a good electron acceptor. Central metal ion exchange of (ZnTPP)-T-II encapsulated into Cu(II)AIMCM-41 gives Cull tetraphenylporphyrin ((CuTPP)-T-II) with almost unit transformation efficiency. We will discuss the interesting reaction which occurred in nanometer-sized pores in terms of the characteristics of the mesoporous silica and the nature of the encapsulated (ZnTPP)-T-II. (C) 2002 Published by Elsevier Science B.V.