Toward tightly bound carboxylic acid-based organic dyes for DSCs: relative TiO2 binding strengths of benzoic acid, cyanoacrylic acid, and conjugated double carboxylic acid anchoring dyes

- Double carboxylic acid acceptor quinoxaline dyes have been synthesized.
- Double anchor dyes bind metal oxides notably stronger than single anchor dyes.
- All dyes show efficient electron injection into a semiconductor.
- This strategy enables multi-components to be anchored in devices with simple acids.

Strong anchoring groups are essential in the fabrication of the highest efficiency dye-sensitized solar cell (DSC) devices and for promoting long-term stability of photosensitizers in DSCs. While many metal-based sensitizers frequently make use of multiple anchors, synthesizing purely organic dyes with multiple anchors, especially those with anchors in direct conjugation with donor structures, has proved challenging. Novel quinoxaline-based dyes utilizing double donor/double acceptor structures can fill this gap in dye design understanding through a novel double donor-π-bridge-double acceptor (DD-π-AA) dye. These dyes have been synthesized with the optical and electrochemical properties, electron injection efficiencies, and relative binding strengths characterized. Fluorescence lifetime measurements show favorable electron injections from all dyes. Submersing dye-sensitized TiO2 plates in a hydrolytic solution reveals desorption rates up to 180 times slower for dyes containing multiple carboxylic acid anchors compared to single acid anchors.

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