Synthesis, Electronic Spectroscopy, Cyclic Voltammetry, Photophysics, Electrical Properties and X-ray Molecular Structures of meso-{Tetrakis[4-(benzoyloxy)phenyl]porphyrinato}zinc(II) Complexes with Aza Ligands

Abstract

The synthesis of the new meso-porphyrin tetrakis[4-(benzoyloxy)phenyl]porphyrin (H2TPBP), the meso-{tetrakis[4-(benzoyloxy)phenyl]porphyrinato}zinc(II) starting material [Zn(TPBP)] (1), and the 1,4-diazabicyclo[2.2.2]octane (dabco), pyrazine (pyz), 4,4′-bipyridine (4,4′-bpy), 4,4′-diaminodiphenylmethane (4,4′-mda), and 4-cyanopyridine (4-CNpy) coordination compounds with [Zn(TPBP)] (2–7) are described. The preparation of the dabco derivative in chlorobenzene leads to a crystalline monomeric five-coordinate zinc porphyrin species (2), whereas the synthesis in dichloromethane gives a five-coordinate zinc metalloporphyrin dimer (3) in the solid state. The pyrazine derivative crystallizes as a bis-pyrazine six-coordinate zinc metalloporphyrin (4). Complex 5 in the solid state is a dimer with 4,4′-bpy as a bridging ligand, whereas the 4,4′-mda species (6) is a five-coordinated monomeric zinc derivative in the solid state. All of structures of 2–6 possess cavities with different dimensions in which solvent molecules are located. The solution UV/Vis spectra of 2–7 exhibit redshifted Soret bands that indicate that these derivatives are five-coordinate zinc(II) porphyrin complexes in solution. UV/Vis titrations show that the association constants of 2–7 are close to those of known five-coordinate zinc(II) meso-porphyrins. The1H NMR spectra of these species confirm this deduction. The photophysical proprieties of 1–7 are similar to those of related zinc(II) meso-porphyrins. The cyclic voltammograms of the H2TPBP free base and 1–7 present a third one-electron reversible oxidation wave. Single-layer diode devices of the [iridium tin oxide/zinc porphyrin/aluminum] configuration show relatively low turn-on voltages.