Design, synthesis and photophysical study of luminescent tetra(iscyano) rhenium(I) complexes

Abstract

This thesis presents the design, synthesis, characterization and photophysical properties of new classes of luminescent tetraisocyano rhenium(I) complexes. A new series of rhenium(I) tetra(isocyano) diimine complexes, [Re(CNR)4(N-N)]+, with various isocyanide and diimine ligands of different electronic nature (where R = 4-IC6H4, 4-BrC6H4, 4-Br-2,6-(CH3)2C6H2, 2,4,6-Cl3C6H2, 2,4,6-Br3C6H2, 2,4-Cl2-6-CH3OC6H2; N-N = 2,2'-bipyridine, 1,10-phenanthroline, 4,4'-di-tertbutyl- 2,2'-bipyridine, 4,4'-dimethoxy-2,2-bipyridine and 1-methyl-2-(2'-pyridyl)imidazole) has been synthesized and characterized. These complexes were characterized by 1H NMR, IR, mass spectrometry and elemental analysis. The X-ray crystal structures of three of the complexes [Re(4-IC6H4NC)4(phen)]ClO4, [Re(4- BrPhNC)4(bpy)]PF6 and [Re(2,6-(CH3)2PhNC)4(bpy)]PF6 were also determined. These complexes were found to show orange to red photoluminescence, which were assigned as derived from the 3MLCT [dπ(Re) → π*(N-N)] excited state origin. It has also been demonstrated that the emission properties of these complexes could be readily tuned through the substituents on the isocyanide and diimine ligands. The photophysical properties, solvatochromic behaviour and the structure-property correlation of these complexes were investigated in details by UV-vis and emission spectroscopy. It is worth paying attention that some of these complexes are extremely sensitive to the polarity and rigidity of the medium. The emissive excited state was further studied by nano-second transient absorption spectroscopy. The electrochemical properties of these complexes by cyclic voltammetry have also been described. In addition to the complexes with neutral diimine ligands, another new classes of luminescent tetra(p-bromophenylisocyano) cyclometalated rhenium(I) complexes, [Re(CNC6H4Br)4(R1-pyind)] (where R1-pyind are substituted 2-(2'-pyridyl)indoles, which is prepared by the reaction of the corresponding facial tricarbonyl cyclometalated rhenium(I) complexes fac-[Re(CO)3(H2O)(R1-pyind)] have been developed. These complexes were characterized by 1H NMR, IR, mass spectrometry and elemental analysis. The X-ray structure of one of the facial tricarbonyl cyclometalated rhenium(I) complexes has also been determined. The UV-vis absorption, emission and electrochemical properties of these tricarbonyl and tetra(pbromophenylisocyano) cyclometalated rhenium(I) complexes have also been studied.