Confinement-induced physicochemical and optical modulation of metalloporphyrins within mesoporous silica MCM-41

Amino-functionalized mesoporous silica MCM-41 was used as a confined host for free-base tetraphenylporphyrin (TPP) and Zn-, Co-, and Fe-tetraphenylporphyrins (M-TPP). The composites were prepared by impregnation and characterized using X-ray diffraction (XRD), nitrogen (N 2 ) adsorption–desorption, diffuse-reflectance ultraviolet–visible (UV–Vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and time-resolved fluorescence spectroscopy. The ordered MCM-41 structure was retained after functionalization and porphyrin incorporation, while the Brunauer–Emmett–Teller (BET) surface area decreased from 947 m 2 /g for Si-MCM-41 to 47–67 m 2 /g for the porphyrin-containing composites. Diffuse-reflectance UV–Vis measurements showed Soret-band red shifts of 16 and 24 nm for ZnTPP-M and CoTPP-M, respectively, together with red shifts of the Q bands. PL measurements revealed emission blue shifts of 15 nm for TPP and 19 nm for FeTPP after incorporation. The observed spectral changes are attributed to the combined effects of the local silica environment, host–guest interactions, confinement, and possible porphyrin aggregation. FTIR spectroscopy revealed changes in the chemical environment of the aminopropyl-functionalized silica after porphyrin incorporation, although the available data do not independently establish specific metal–nitrogen coordination. Multiexponential fluorescence decay profiles indicated heterogeneous excited-state environments within the composites. Overall, the results demonstrate that amino-functionalized MCM-41 modifies the physicochemical and photophysical behavior of incorporated porphyrins and provide a basis for the future development of supported porphyrin materials for optical sensing and photocatalytic applications.