| Porphyrins seem to be an ideal alternative for dye sensitized solar cells. Porphyrins are known to have favorable light harvesting properties, but have for years been inferior to ruthenium dyes. Work has been done to overcome the limitations of porphyrins so they can become as efficient as the ruthenium based dyes. Extension of the p system of a porphyrin dye broadens and red shifts the absorption, and introducing a push-pull functionality on the periphery helps facilitate electron injection into the semiconductor of the cell. Tuning the molecule to optimize these properties has helped bring porphyrins up to speed with the ruthenium based dyes. The current challenge is now the synthetic issues that are seen in these molecules. It is also believed that through exploring new synthetic methodologies, enhancements can be made in the efficiencies as well. With these goals in mind, new synthetic routes and functionality are desired. We have developed a concise synthetic method to prepare push-pull benzoporphyrins in 4 steps from a dibromo starting porphyrins. Using a twofold Heck reaction, 6p-electrocyclization, and aromatization we can introduce both new functional groups to the porphyrin periphery and our electron withdrawing and electron donating groups to give our desired push-pull characteristic. |
