Luminescent rhenium(I) diimine complexes with cyano or isocyano ligands and thermochromic isocyano rhodium(I) diimine complexes : design, synthesis and photophysics

發光含氰或異腈錸(I)二亞胺配合物及熱致變色異腈銠(I)二亞胺配合物 : 設計, 合成與光物理

Student thesis: Doctoral Thesis

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Author(s)

  • Tso Lun LO

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date14 Feb 2014

Abstract

Luminescent rhenium tricarbonyl diimine complexes are known to show interesting photophysical and photochemical properties. Through the functionalization of their diimine ligand, these complexes can function as chemosensors, bio-probes, photo-catalysts or emissive materials for light emitting devices (LEDs). However, once the diimine ligand is functionalized for the applications, the properties of these complexes are difficult to modify or fine-tune. On the other hand, most of the rhenium tricarbonyl diimine complexes are not suitable for device applications because many of these highly emissive complexes are positively charged and therefore unsublimable. To improve the tunability and processability of the rhenium(I) diimine luminophores, design and study new classes of rhenium(I) diimine complexes through the incorporation of more than one ancillary ligands, including the isoelectronic isocyanide or cyanide ligands as well as the development of a new series of novel anionic diimine ligands have been carried out. These new classes of rhenium(I) complexes have also been subjected to detailed photophysical and electrochemical investigation. In order to enhance the tunability of the rhenium(I) diimine luminophore, we have designed a new readily tunable rhenium(I) diimine complex system through the replacement of the carbonyl ligands with the isoelectronic isocyanide ligands. Novel and highly selective photo-induced ligand substitution reactions have been developed to synthesize the new target complex system with general formula of cis,cis-[Re(CO)2(CNR)2(N-N)]PF6 (R = C6H2Cl3, C6H4Cl, C6H2Me2,Br, C6H5C6H4, (CH3)2C6H3, (CH3)2NC6H4, tBu, nBuC6H4; N-N = phen, ph2phen, tBu2bpy). The new photo-substitution reaction was investigated and optimized by in-situ IR spectroscopy. The X-ray crystal structure of one of the target complexes has also been determined. All these complexes display intense luminescence with quantum yield up to 37 %. The photophysical and electrochemical properties of these complexes were investigated. To provide further insight into the emissive excited states of these complexes, transient absorption spectroscopy has also been carried out. With the photo-ligand substitution reactions, we have also extended our works to develop highly environmental sensitive dicarbonyl dicyanorhenate(I) diimine complexes cis,trans-[Re(CO)2(CN)2(N-N)]M(N-N = phen, Br2phen, 4,4'-tBu2bpy, bpy; M = K, nBu4N). All these complexes were well-characterized by various spectroscopic techniques. The structures of two of the complexes were determined by X-ray crystallography. Their photophysical properties including the strong solvatochromism and metallochromism were also studied. In addition to their interesting photophysical properties, applications of these complexes as photocatalysts for CO2 reduction to CO have also been investigated. In addition to developing of new families of Re(I) diimine luminophores through the introduction of various ancillary ligands, the design of neutral luminescent rhenium(I) diimine complexes through the incorporation of anionic borate-containing diimine ligands (2-[1-(tris(pentfluorophenyl)-borane)]-imidazol-2-yl)pyridine (pimBF) and 2-[1-(triphenyl-borane)]-imidazol-2-yl)pyridine (pimB)) into the cationic tricarbonyl rhenium(I) complex system has also been described. These complexes were characterized and their photophysical and electrochemical properties were studied. The effect of the substituents of the anionic triarylborate moieties on the photophysical properties of these complexes has also been discussed. Inspired by the interesting photophysical properties as well as the readily tunable features of the isocyano rhenium(I) diimine complexes, a new family of square planar bis(phenylisocyano) rhodium(I) diimine complexes with the formula of [Rh(N- N)(CNR)2]BF4 (N-N = bpy, tBu2bpy, Cl2bpy Me2bpy, (MeO)2bpy, Br2phen; R = C6H5 ((CH3)2HC)2C6H3, ClC6H4, Cl3C6H2, Br3C6H2, Me2C6H3) has been designed, synthesized and characterized. Three of these complexes were also structurally characterized by X-ray crystallography. Interestingly, the solutions of all these complexes display theromochromism, which is attributable to the change of the aggregation and Rh-Rh interaction of these complexes. Different aggregated forms of one of the complexes have also been determined by the X-ray crystallography. The photophysical properties including the thermochromism have been studied by UV-Vis absorption spectrometry at various temperatures. To provide further insights into the aggregation affinity of these complexes, the enthalpy (ΔH) and entropy (ΔS) changes of the dimerizations of these complexes have been determined. Apart from their thermochromic and aggregation properties, these square planar complexes can also serve as DNA metallointercalators. The DNA binding and intercalating properties of these complexes were investigated by UV-Vis absorption spectroscopy and DNA unwinding assay.

    Research areas

  • Rhenium compounds, Rhodium compounds, Luminescent probes, Ligands (Biochemistry)