The synthesis, characterization, electrochemical and photophysical properties of the phosphonate-derivatized Carbazole (CBZ) and boron dipyrromethene (BODIPY) chromophores in the dyes, BODIPY(CBZ)2PO3H2 [8] and BODIPY(Tol)2PO3H2 [7], are described. The oxide-bound dyes have been explored as light absorbers in dye-sensitized photoelectrosynthesis cell (DSPEC) applications. The results of nanosecond transient absorption measurements on SnO2/TiO2 electrodes provide direct evidence for excited-state electron injection into the conduction band of TiO2 following 590 nm excitation. A longer life time for [8] compared to [7] is consistent with extensive intramolecular charge separation between the CBZ and BODIPY units on the surface. Photoelectrochemical studies on [8] on a SnO2/TiO2 photoanode resulted in sustained photocurrents with current maxima of ∼200 μA/cm2 with hydroquinone added as a reductant under 1 sun illumination. On mixed SnO2/TiO2 electrode surfaces, with the added catalyst [Ru(Mebimpy)((4,4′-(OH)2PO-CH2)2bpy)(OH2)]2+ and chromophores [7] and [8], addition of 0.1 M benzyl alcohol resulted in sustained photocurrents of 12 and 35μA/cm2 consistent with oxidation to benzaldehyde.
Badgurjar, D.; Shan, B.; Nayak, A.; Wu, L.; Chitta, R.; Meyer, T. J. Electron-Withdrawing BODIPY Dyes As Visible Light Absorber/Sensitizers on Semiconductor Oxide Surfaces. ACS Appl. Mater. Interfaces 2020, 12 (6), 7768-7776. http://dx.doi.org/10.1021/acsami.9b20167