Photoionization of 10-methylphenothiazine (PC1), N,N',N'-tetramethylbenzidine (TMB), and pyrene (Py) impregnated into mesoporous AIMCM-41 ion-exchanged with Cr(III), as an electron acceptor, to give CrAlMCM-41 was investigated. Cation radicals (PC1.+, TMB.+, Py.+) are produced by 320 nm light at room temperature and characterized by electron spin resonance (ESR) and UV-vis diffuse reflectance spectroscopy. The chromium ion concentration was varied from Si/Cr = 52 to 121. Cr-AlMCM-41 with the intermediate concentration of Si/Cr = 80 exhibits the greatest electron acceptor ability and shows the highest photoionization efficiency photoionized. The photoionization efficiency also depends on the type of photoionizable molecule impregnated into mesoporous Cr-AlMCM-41 with PC, being the most efficiently photoionized. The calcination temperature used before impregnation controls the oxidation state of chromium ions to Cr3+ or Cr5+/Cr6+ which also affects the photoionization efficiency. Cr-AlMCM-41 with Cr5+ gives about 4 times higher photoionization efficiency than with C3+. Cr-AlMCM-41 is shown to be a promising heterogeneous host for the efficient formation of photoinduced cation radicals to achieve long-lived charge separation in solidstate systems.