Photooxidation of alkylphenothiazines in SiMCM-48, AlMCM-48 and VMCM-48 mesoporous molecular sieves

Abstract

Phenothiazine derivatives were introduced into SiMCM-48, AlMCM-48 and VMCM-48 mesoporous molecular sieves by impregnation. Alkylphenothiazine cation radicals (PC_n⁺) were generated by photooxidation within MCM-48 samples and characterized by EPR and diffuse reflectance UV–VIS spectroscopy. A series of VMCM-48 and AlMCM-48 mesoporous molecular sieves with different metal contents were synthesized hydrothermally and increased the PC_n⁺ cation radical photoyield compared with SiMCM-48. The photooxidation efficiency to form PC_n⁺ cation radicals increases in the order SiMCM-48<AlMCM-48<VMCM-48. Increasing the alkyl chain length affects the alkylphenothiazine cation radical photoyield and stability. PC_n⁺ cation radicals are stable in MCM-48 samples at room temperature from several hours to several days. Mesoporous MCM-48 molecular sieves are shown to be effective heterogeneous hosts to achieve long-lived photoinduced electron transfer of PC_n molecules at room temperature.