Electron transfer (ET) reactions of carotenoids (Car), beta-carotene (I), canthaxanthin (II), and 7'-apo-7',7'-dicyano-beta-carotene (III) imbedded in MCM-41 and Ti-MCM-41 were studied as a function of oxidation potential. The ET efficiency in MCM-41 was highest for the carotenoid with the lowest oxidation potential. The presence of Ti4+ in the framework of MCM-41 enhanced the ET efficiency of all carotenoids, but the enhancement did not depend on oxidation potential. The enhancement depends on whether complexes are formed between carotenoids and Ti4+. Complexes were formed with I and III but not with II. The presence of Ti4+ results in a large blue shift of the maximum absorption wavelength due to changes in the carotenoid conformation.