Photochemical Synthesis of Intensely Luminescent Isocyano Rhenium(I) Complexes with Readily Tunable Structural Features

Abstract

A new class of readily tunable isocyano rhenium(I) diimine luminophores, cis,cis-[Re(CO)(2)(CNR)(2)(N-N)](+) (R=2,4,6-Cl(3)C(6)H(2), 4-ClC(6)H(4), 4-Br-2,6-(CH(3))(2)C(6)H(2), 2,6-(CH(3))(2)C(6)H(3), 4-[(CH(3))(2)N]C(6)H(4), 4-(C(6)H(5))C(6)H(4), 4-nBuC(6)H(4), tBu), has been synthesized in high yield by a highly selective photochemical substitution reaction. These complexes were characterized by (1)H NMR and IR spectroscopy, mass spectrometry, and elemental analysis. The X-ray crystal structures of one of the complexes and one of the precursor complexes for the photosubstitution reaction were also determined. As the isocyanide ligands are readily tunable, complexes with excellent solubility in benzene or other nonpolar solvents could be designed through slight modification of the isocyanide ligands with a short nBu substituent. With the characteristic strong infrared absorptions of the carbonyl (C≡O) and isocyanide (C≡N) stretches as well as the high solubility of the reactant and product in benzene, which is the solvent for the photoreaction, the photosubstitution reaction of [Re(CO)(3)(nBuC(6)H(4)NC)(2)Br] with 4,4'-di-tert-butyl-2,2'-bipyridine was also studied by in situ IR spectroscopy. The photophysical and electrochemical properties of these complexes were also investigated. Except for the complex with [(CH(3))(2)N]C(6)H(4)NC ligands, all complexes displayed intense luminescence with quantum yields of up to 0.37 in degassed CH(2)Cl(2) solution at room temperature. These emissions were assigned as the phosphorescence derived from the metal-to-ligand charge transfer [dπ(Re)→π*(N-N)] excited state. The emissive excited states of these complexes have also been characterized by transient absorption spectroscopic studies. The capability of tuning the emissive excited-state energy through the modification of the isocyanide ligands could be reflected by the significant shifting of the phosphorescence from 530 to 620 nm with the same phenanthroline ligand.

Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato Complexes: Synthesis, Characterization, and Photophysical, Electrochemical, and Computational Studies

“…5-75.88, which is typical for diimine transition-metal complexes. [7,13] The ReÀCO and ReÀCNBR 3 bond distances are in the range of 1.90-1.97 and 2.07-2.12 , respectively, which are comparable to those observed in other carbonyl isocyano rhenium(I) complexes. [7b,c,e, 14] For the isocyanoborate ligands in these crystal structures, they are all slightly deviated from linearity, with CNÀB angles of 168.3-178.28.…”

“…This is typically observed in MLCT phosphorescent emitters. [7,18] As a result of the blue-shifted 3 MLCT excited state in these media, the emissions of some of these complexes (1 a-6 a, 3 c, 3 e, and 4 b) changed from the Table S3). The vibrational progressional spacings calculated from the well-resolved structured emission peak maxima were in the range of 1200-1300 cm…”

“…As with other tricarbonyl rhenium(I) diimine complexes, [2,7] these complexes also exhibited one irreversible wave or quasireversible oxidative couple with E pa or E 1/2 in the range of + 1.44 V to + 1.85 V vs. SCE, attributable to Re I/II metal-centered oxidation. The oxidation potentials not only showed strong dependence on the p-accepting ability of the ancillary ligand (cyanide or isocyanoborate ligand) but also slightly varied with the electronic properties of the diimine ligands.…”

“…All of the isocyanoborato complexes exhibited intense ligand-centered (LC) p-p * absorptions of the diimine and isocyanoborate ligands with molar absorptivity on the order of 10 4 dm 3 mol À1 cm À1 in the UV region (< 320 nm). [2,7] At the lower energy region, these complexes showed moderately intense transitions with molar absorptivity on the order of 10 3 dm 3 mol À1 cm À1 in the region of 310-380 nm. With reference to previous spectroscopic studies on the isocyano carbonyl rhenium(I) diimine complexes, these absorptions were ascribed to the mixing of the metal-toligand charge transfer (MLCT) transitions of [dp(Re)!p * (N^N)], [dp(Re)!p * (CNBR 3 )] and the ligand-to-ligand charge transfer (LLCT) [p(CNBR 3 )!p * (N^N)] transition.…”

“…[6] This is because many of the highly emissive rhenium(I) diimine complexes are cationic and therefore unable to be processed by vacuum deposition. Regarding our work on isocyano rhenium(I) diimine luminophores, [7] we have demonstrated the use of anionic isocyano tris(pentafluorophenyl)borate ligand in the development of strongly sky-blue phosphorescent chargeneutral rhenium(I) complexes, which are stable for vacuum sublimation and suitable for electroluminescent device application. [8] To design phosphorescent materials from these isocyanoborato complexes, it is crucial to understand their electronic properties as well as their photophysics.…”