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Reports: ND351962-ND3: Synthesis and Characterization of Dyads Capable of Achieving Photoexcited Two-Electron Charge-Separated States

Raphael G. Raptis, PhD, Florida International University

Following the relocation of our research group from the University of Puerto Rico to Florida International University during the Fall 2013 semester, one graduate student worked on the synthesis of electron donor-acceptor conjugates consisting of the multi-electron acceptor complex [Fe8(m4-O)4(m-4-R-pz)12L4], [Fe8], and electron donor transition metal complexes. Our new work has been advised by the following two observations: First, our initial efforts at connecting the electron donor complexes to pyridine functionalites dangling from the [Fe8] complex have either resulted in intractable mixtures of products, or gave products that upon UV irradiation acted as energy transfer media, rather than the desired electron-transfer conjugates. Second, we have previously shown that phenolates coordinate readily to the [Fe8] moiety by straightforward ligand substitution reactions, forming products of the type [Fe8(m4-O)4(m-4-R-pz)12L4-x(OAr)x]. For the above reasons, the synthesis of new electron donor complexes containing ligands with available, sterically unhindered phenol functions was our strategic method of choice. Recent work has focused on the synthesis, characterization and electrochemical evaluation of metal complexes of (1) hydroxyl-functionalized terpyridine and (2) bipyridine.

(1) Hydroxyterpyridine (tpy-OH) was prepared by a literature method. Five new transition metal complexes -- [Ru(tpy-OH)(bpy)Cl]Cl, [Ru(tpy-OH)2]Cl2, [Fe(tpy-OH)2](ClO4)2, [Co(tpy-OH)2](ClO4)2, and [Cu(tpy-OH)2](ClO4)2 – were synthesized and characterized by single crystal X-ray structure determination and elemental analysis, while their UV-vis spectra and cyclic voltammograms were also recorded. Complex [Ru(tpy-OH)(bpy)Cl]+was also characterized in solution by ESI-MS, confirming its solid state formula.

(2) Previously prepared [M{bpy-(OH)2}3]2+ (M = Ru and Co) and [M{bpy-(OH)2}2]2+ (M = Cu and Zn) have now been fully characterized by X-ray crystallography, elemental analysis and UV-Vis spectroscopy.