Ultrafast Photooxidation of Mn(II)−Terpyridine Complexes Covalently Attached to TiO2 Nanoparticles

This paper reports visible-light sensitization of TiO 2 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 (H 2 O) 3 (catechol-terpy)] 2+ /TiO 2 (terpy = 2,2‘:6,2‘ ‘-terpyridine) complex, attached to the TiO 2 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.