Elucidating the Role of the Metal Linking Ion on the Excited State Dynamics of Self-Assembled Bilayers

Abstract

Metal ion-linked, self-assembled multilayers on nanocrystalline metal oxide surfaces have recently emerged as an effective strategy for manipulating energy and electron transfer dynamics at organic–inorganic interfaces. The choice of metal ion can have a large impact on the stability, loading concentration, and other properties of the films. Here we report our investigation into the role of the linking ion on the subnanosecond excited state dynamics in the bilayer films (TiO2–B–M–RuP). While metal linkers like CdII, LaIII, SnIV, ZnII, and ZrIV are photochemically inert, paramagnetic linking ions such as CuII, FeII, and MnII quench the excited state of the dye with a rate constant on the order of 108 s–1. The absence of new spectral features in the transient absorption spectrum suggests that energy transfer, and not electron transfer, is responsible for the excited state quenching. On TiO2, the electron injection rate for TiO2–B–M–RuP is an order of magnitude slower (∼1 × 109 s–1) than for the dye directly...