Dye-Sensitized NiO photocathode based on rhodamine B-Appended Iridium(III) complex for Photoelectrochemical assay

Abstract

A dye-sensitized NiO photocathode with an iridium complex serving as both target recognition unit and photosensitizer has been assembled for Hg2+ detection. In the molecular design of the iridium complex, rhodamine B is appended to the ancillary ligand as a target recognition chromophore, and the anchoring group is located on the cyclometalated ligand, that is the part of HOMO, so as to favor hole injection from the dye’s excited state to the valence band (VB) of NiO. A cathodic PEC assay for Hg2+ detection was developed with a turn-on photocurrent response through assembling the as-designed iridium complex on the surface of the NiO. In the presence of Hg2+, opening of the spirolactam ring in the xanthene moiety of the complex results in an enhanced absorbance at 570 nm, which correspondingly leads to an improved photocurrent due to efficient photosensitization. Benefiting from the precise recognition of the molecular probe, controllable assembly process and inherent advantage of cathodic PEC assay, the simple PEC assay presents superior sensitivity to Hg2+ detection, about 4 orders of magnitude higher than that of iridium complex analogue as fluorescent probe, as well as excellent selectivity, and remarkable reproducibility.