Pd-catalysed synthesis of blue organic dyes and their application as sensitizers for near-IR absorbing Dye-Sensitized Solar Cells

Since their discovery in 1991, Dye-Sensitized Solar Cells (DSSC) have been considered a very promising technology to convert solar energy in electric current due to their low cost of production, their innovative aesthetic properties and their easy integration in buildings and objects. The dye, which can be a completely organic molecule, is the photoactive material and is considered the heart of a DSSC.[3] The introduction of an auxiliary acceptor group inside the classical D-?-A motif of the organic sensitizers can play a key role to achieve dyes with a very intense and broad light absorption spectrum and high incident photon-to-current conversion efficiencies. Aiming to this goal, we selected as new auxiliary acceptor group the (E)-3,3'-bifuranylidene-2,2'-dione, a strong electron-withdrawing system which was firstly prepared in 1882. The synthesis of this dye has been optimized and its derivatization using Pd-catalysed cross-coupling reactions has been firstly accomplished. Then, two new D-A-?-A dyes containing the (E)-3,3'-bifuranylidene-2,2'-dione as auxiliary acceptor group have been designed, synthesized and characterized: the two new dyes showed an intense blue color in solution and, when adsorbed on a TiO2 electrode, both a broad absorption of the red/near-infrared light between 500 and 800 nm and right electrochemical potentials for a proper use in DSSCs.