Synthesis, Characterizations, and Intramolecular Quenching Behavior of an Axially-Linked Trinuclear Molecular Wire Containing Ruthenium(II) Porphycenes

Abstract

ABSTRACT:A new trinuclear complex [Ru(TPrPc)(CO)] 2 [Ru(pytpy) 2 ](PF 6 ) 2 (TPrPc = 2,7,12,17-tetra-npropylporphycenato dianion and pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) has been synthesized and characterized as the first example of a discrete molecular wire containing metalloporohycenes as a building block. The trinuclear complex shows multiple-step redox behavior in 0.1 M n-Bu 4 NPF 6 -dichloromethane. The mononuclear [Ru(pytpy) 2 ] 2+ precursor shows emission at 640 nm (deaerated acetone, 298 K) upon illumination at the metal-to-ligand charge transfer (MLCT) band at 495 nm, but the trinuclear molecular wire is found to be non-emissive upon photoexcitation at the central [Ru(pytpy) 2 ] 2+ entity, indicating an efficient quenching ability of the axially-linked, ruthenium(II)-porphycene chromophores in an intramolecular fashion.Porphycene is one of the constitutional isomers of porphyrin with a tetrapyrrolic N 4 cavity in a rectangular shape [1][2][3][4]. Chemistry of porphycene and metalloporphycene complexes [5,6] has been of considerable interest due to their intense absorption in the visible region [7], utility as photodynamic therapy (PDT) agents [8], and substrate binding and activation [9]. Recently, porphycenes have been used as functional building blocks incorporated into carbon nanomaterials [10].Stable axial coordination in metalloporphyrin complexes has been convenient and powerful molecular approach to construct a novel series of redox-and photo-functional molecular assemblies, such as molecular wires via coordinative linkage [11]. Actually, the construction of well-defined, metalloporphyrin-based ensembles via axial coordination has constituted active research areas in the metallosupramolecular chemistry [12,13]. As a multicomponent molecular wire, Branda and the coworker have previously described [17,18] in acetone for 24 h at room temperature and, after workup, isolated as a bluish green solid in a 58% yield [19]. The compound was fully characterized by various spectroscopic methods, mass spectrometry, and cyclic voltammetry.1 H NMR spectroscopy (acetone-d 6 ) reveals the formation of the expected trinuclear structure comprised of [Ru(TPrPc)(CO)] and [Ru(pytpy) 2 ] 2+ moieties in a 2:1 ratio. A noticeable ring current effect of the TPrPc 2-ligand is seen for a resonance due to 2,6-H of the pyridyl group in pytpy which appears at  1.18. ESI-MS shows a parent mass envelope at m/z = 967.6 with a peak interval of 0.5, indicating formation of the anticipated trinuclear complex with an overall charge of +2. In addition, an IR spectrum (KBr pellet) exhibits a strong (CO) peak ascribed to the [Ru(TPrPc)(CO)] group at 1930 cm -1 which is comparable with that of the monomeric precursor 2 (1932 cm -1 ).