Photoionization of N-alkylphenothiazines in mesoporous Me-AlMCM-41 containing ion-exchanged transition metal ions Me = Ni(II), Fe(III), and Cu(II) was investigated. N-alkylphenothiazine cation radicals (PCn+) are produced by 320 nm light at room temperature and characterized by electron spin resonance and ultraviolet-visible diffuse reflectance spectroscopy. Me-AlMCM-41 materials are shown to be efficient heterogeneous hosts for the photoinduced formation of long-lived PCn+ cation radicals, indicating efficient photoinduced charge separation. Ni-AlMCM-41 shows the highest photoionization efficiency compared to Fe-AlMCM-41 and Cu-AlMCM-41. The photoionization efficiency depends on the metal ion type and concentration ion-exchanged into mesoporous Me-AlMCM-41 molecular sieves. Also, as the alkylphenothiazine alkyl chain length increases from methyl to hexadecyl, the photoionization yield decreases.