Pyridine-N-Oxide 2-Carboxylic Acid: An Acceptor Group for Organic Sensitizers with Enhanced Anchoring Stability in Dye-Sensitized Solar Cells

A D‐π‐A organic dye carrying a pyridine‐N‐oxide 2‐carboxylic acid anchoring group (BC1) was synthesized together with two analogs lacking the N‐oxide (BC2) or the carboxylic acid moiety (BC3). The distribution and energy of their molecular orbitals was determined, and modelling of their spectroscopic properties was performed through a TD‐DFT computational study. The photo‐ and electrochemical properties of the dyes were assessed together with their desorption kinetics from nanocrystalline TiO2. In solution, the absorption spectra of dyes BC1 and BC3 were red‐shifted compared with BC2, with the maximum absorption wavelength influenced by the dye protonation level. The 2‐substituted carbonitrile dye BC3 was not adsorbed on the titania surface. On the other hand, the pseudo‐first order desorption rate constants of BC1 and BC2 suggest that BC1 was removed from TiO2 more slowly than BC2 a reference cyanoacrylate dye, demonstrating that simultaneous use of the N‐oxide and the carboxylic acid anchoring functions enhanced the stability of the dye/semiconductor assembly. When used as a photosensitizer for dye‐sensitized solar cells, the photovoltaic performance of BC1 was better than BC2, which corresponds to approx. 66 % of that recorded with the reference dye.