Long-lived (minutes) photoinduced charge separation in a structured periodic mesoporous titania containing 2,4,6-triphenylpyrylium as guest

Abstract

2,4,6-Triphenylpyrylium (TP⁺), an electron acceptor, has been included inside the channels of two ordered mesoporous titania (mpTiO₂). MpTiO₂ contain anatase nanoparticles (3–5 nm) templated by cetyltrimethylammonium and differ by the presence or absence of silica domains as binders of the structure. UV irradiation of TP–mpTiO₂ gives rise to a strong EPR signal. This behaviour was not observed for related materials in which TP⁺ was included inside the channels of MCM-41 or the cavities of zeolite Y. Also, transient spectroscopy shows remarkable differences between TP⁺ included in mpTiO₂ (charge separation) and in porous silicates (triplet excited state). Based on EPR and laser flash spectroscopic evidence, the occurrence of photo-induced electron transfer from TiO₂ as the donor to TP⁺ as the acceptor leading to a long-lived (minutes at room temperature) charge separated state is proposed.