A new series of tunable isocyano rhenium(I) diimine complexes, [Re(CO)(CNR)3(N-N)]PF6 and [Re(CO)(Lx)(CNC6H4Cl-4)2(phen)]PF6, (R = C6H5, 4-BrC6H4, 4-ClC6H4, 4-MeOC6H4, 2,6-iPr2C6H3; N-N = 1,10-phenanthroline (phen), 5,6-dibromo-1,10-phenanthroline (Br2phen), 4,4'-di-tert-butyl-2,2'-bipyridine (tBu2bpy); Lx = MeCN, pyridine and PPh3) have been reported. New synthetic strategies including photochemical substitution and thermal carbonyl ligand substitution reaction mediated by Me3NO as decarbonylating agent have also been developed to selectively synthesize the facial and the meridional isomers of [Re(CO)(CNR)3(N-N)]PF6. With these synthetic routes, complexes containing isocyanide and diimine ligands of diverse electronic and steric nature have been prepared. Moreover, the Me3NO mediated carbonyl ligand substitution reaction was also demonstrated to be useful for incorporating other ancillary ligands into the isocyano Re(I) diimine systems. The X-ray crystal structures of both the facial and meridional isomers of target complexes [Re(CO)(CNR)3(N-N)]PF6 as well as one of the complex precursors were determined. These complexes exhibit orange to red photoluminescence at room temperature, which was ascribed to 3MLLCT [dπ(Re) → π*(N-N)] phosphorescence. Detailed spectroscopic and electrochemical studies on these complexes have also been performed. With these isocyano Re(I) diimine complexes, the physical and excited state properties can be tailored and fine-tuned through a judicious choice and modification of the isocyanide or diimine ligands. With the bridging isocyanide ligands, a series of luminescent dinuclear complexes, cis,trans-[(N-N)(PPh3)(CO)2Re(CN-R'-NC)Re(CO)2(PPh3)(N-N)]2+, has also been synthesized. The mononuclear rhenium(I) complex analogues were also prepared. The X-ray crystal structures of two of these dinuclear complexes were also determined. The photophysical and electrochemical properties of these complexes have also been described. Detailed study showed that these complexes are highly emissive with emission quantum yields higher than other Re(I) diimine complexes with similar energy. A further extension of this work was done to synthesize another novel series of homotrinuclear cyano-bridged rhenium(I) complexes {[Re]'[Re][Re]'}+ {[Re]' = -[ReI(CO)2(LL)(PPh3)]; [Re] = -[NC-ReI(phen)(CO)2-CN]-; LL = diimine, diphosphine or two carbonyl ligands}. The X-ray crystal structures of most of the trinuclear complexes have been determined, through which the different relative orientations of peripheral to central rhenium(I) units in these complexes were revealed. With exception of trinuclear complex with Br2phen ligand on the peripheral complex units, which is non-emissive, all other trinuclear complexes show orange to red luminescence. The photophysics and electrochemistry of these trinuclear Re(I) complexes have also been reported. Detailed photophysical studies showed that the emission of these complexes are ascribed to be derived from the 3MLCT [dπ(Re) → π*(phen)] excited state of the central rhenium unit. The strong electronic mixing and communication between the two peripheral rhenium(I) centers in all of these trinuclear complexes was revealed in the electrochemical study.