Inhibited interlayer electron transfer in metal ion linked multilayers on mesoporous metal oxide films

The incorporation of dye-electron donor motifs on metal oxide surfaces is a common strategy to increase dye regeneration rate, slow recombination, and improve overall dye-sensitized device performance. Here we used zinc ion linked multilayer assembly of a dye (N3) and a cobalt polypyridyl electron donor (Co) on TiO2 as an alternative to traditional covalently linked dye-donor systems. The formation of the TiO2-N3-Zn-Co multilayer was monitored using UV–Vis and ATR-IR and we introduced inductively coupled plasma mass spectrometry as a means of quantifying the surface loading of spectroscopically obscured molecules like Co. Interestingly, and contrary to the original intent, the addition of Co electron donor impeded the dye-sensitized device in nearly every performance metric. Transient absorption measurements indicate that both excited state quenching of N3 by Co and Co to N3+ electron transfer are slower than the intrinsic excited state decay and recombination, respectively. We suggest that the geometric restriction imposed by the metal ion linked architecture sufficiently slows electron transfer such that Co is effectively inert in this assembly. While this bilayer did not improve device performance, these insights may guide new design strategies that will improve performance and/or will be of use in other applications where electron transfer is not desired but say communication of spin and/or magnetic moment is needed.