Ultrafast photooxidation of Mn(II)-Terpyridine complexes covalently attached to TiO2 nanoparticles

This paper reports visible-light sensitization of TiO2 nanoparticles by surface modification with Mn(II)-terpyridine complexes, as evidenced by UV-vis spectroscopy of colloidal thin films and aqueous suspensions. Photoexcitation of the [Mn-II(H2O)(3)(catechol-terpy)](2+)/TiO2 (terpy = 2,2':6,2' '-terpyridine) complex, attached to the TiO2 surface, leads to interfacial electron transfer within 300 fs as indicated by ultrafast optical pump-terahertz probe transient measurements and computational simulations. Photoinduced interfacial electron transfer is accompanied by Mn(II) -> Mn(III) photooxidation. The half-time for regeneration of the Mn(II) complex is ca. 23 s (at 6 K), as monitored by time-resolved measurements of the Mn(II) EPR signal.