Synthesis of Ruthenium Tris‐Diimine Photosensitizers Substituted by Four Methylphosphonate Anchoring Groups for Dye‐Sensitized Photoelectrochemical Cell Applications

The design and synthesis of ruthenium tris‐diimine photosensitizers appropriately functionalized to be (i) anchored onto transparent conductive oxides (TCO) and (ii) covalently coupled with a water‐splitting catalyst represents an important target for solar fuel production in dye‐sensitized photoelectrochemical cells (DS‐PECs). In this study, two different synthetic routes to prepare heteroleptic [Ru(4,4′‐(CH2PO3Et2)2‐bpy)2(N^N)](PF6)2 complexes are evaluated, the scope and limitations of the organometallic pathway involving half‐sandwich η6‐arene ruthenium complexes as synthetic intermediates being especially studied. The spectroscopic and electrochemical characterization of a series of novel structures varying by the nature of the third diimine N^N ligand is reported. Two procedures for the synthesis of bis‐heteroleptic ruthenium tris‐diimine photosensitizers bearing four methylphosphonate anchoring groups are evaluated. Their spectroscopic and electrochemical characterization is reported, and the preparation of an alkyne‐substituted complex is highlighted, opening novel perspectives in the field of dye‐sensitized photoelectrochemical cells