Luminescent and Redox-Active Iridium(III)-Cyclometalated Compounds with Terdentate Ligands

Abstract

Two novel bis-terdentate Ir(III)-cyclometalated complexes, [Ir(L1)(L1(-))](2+) (1) and [Ir(L1(-))(2)](+) (2), have been prepared (L1 is 2,6-bis(7'-methyl-4'-phenyl-2'-quinolyl)pyridine; L1(-) is its mono-anion, see Figure 1). To the best of our knowledge, 1 and 2 are the first luminescent and redox-active Ir(III)-cyclometalated bis-terdentate compounds. In acetonitrile solution, on oxidation, 2undergoes a reversible, metal-centered, one-electron oxidation at +1.40 V, whereas 1 does not exhibit any oxidation process up to +2.00 V. On reduction, both compounds undergo four reversible ligand-centered one-electron processes. The absorption spectra of the compounds are dominated by moderately intense (epsilon in the 10(3)-10(4) M(-)(1) cm(-)(1) range) spin-allowed metal-to-ligand charge-transfer (MLCT) bands at wavelengths longer than 350 nm and by intense (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range) ligand-centered (LC) bands at shorter wavelengths. The complexes exhibit an intense luminescence both at 77 K in MeOH/EtOH, 4:1 (v/v), rigid matrix (1, lambda(max) = 592 nm, tau = 20 &mgr;s; 2, lambda(max) = 598 nm, tau = 9 &mgr;s) and at room temperature in deoxygenated acetonitrile solution (1, lambda(max) = 620 nm, tau = 325 ns, Phi = 0.005; 2, lambda(max) = 630 nm, tau = 2.3 &mgr;s, Phi = 0.066). In all cases, the emission is assigned to triplet MLCT levels (namely, Ir --> L1 and Ir --> L1(-) in 1 and 2, respectively).

Detailed Description of the Metal‐to‐Ligand Charge‐Transfer State in Monoterpyridine IrIII Complexes

“…A reversible one-electron oxidation wave was also observed for the other iridium complexes at around 1.69 V. Several reports in the literatures indicate that these processes are due to the removal of the metal-localized electron. [24,25] At negative potentials, complex 2 exhibits a reversible one-electron process at -1.04 V. A similar pattern is observed for complex 3 at -1.18 V. By comparison with the related complexes, these processes can be assigned to the reduction of the terpyridine ligand. The LUMO may be the π* orbital on the terpy derivatives.…”

“…For complex 1, a reversible one-electron oxidation wave was observed at 1.69 V. In general, the Ir IV /Ir III redox couple in iridium(III) complexes with terpyridine ligands cannot be observed in a conventional potential window. [24] This low oxidation potential value reflects the increase in the electronic density at the Ir center. A reversible one-electron oxidation wave was also observed for the other iridium complexes at around 1.69 V. Several reports in the literatures indicate that these processes are due to the removal of the metal-localized electron.…”

Tuning the Excited‐State Energy of the Organic Chromophore in Bichromophoric Systems Based on the RuII Complexes of Tridentate Ligands

“…The separation between the second and third reduction processes is in the range 610-660 mV for all of the complexes (leaving aside 3 e, whose irreversible third process makes the comparison impossible), in good agreement with the electron-pairing energy in tpy-type ligands. [42] Absorption spectra and photophysical properties: The electronic absorption and photophysical data of the new complexes are shown in Table 3. Representative absorption and emission spectra are shown in Figures 5-8.…”

“…[16,17] However, biphenyl, phenanthryl and anthryl groups, which are present in 2 b, 2 c and 2 d, respectively, have no sizeable effect on the MLCT lifetime at room temperature. The reason is that the lowestenergy MLCT state in these complexes is so low lying that thermal population of the relevant aromatic organic triplets (whose lowest-energy triplet is that of the 9-aryl anthracene chromophore, at about 685 nm [16,42,43] ) is ineffective; furthermore, the intrinsic decay rates of aromatic hydrocarbons and MLCT triplets should be taken into consideration. As far as 2 e is concerned, this species bears a brominated anthracene and the electron-withdrawing effect of the bromo substituent lowers the energy of the anthracene-based triplet state.…”

Synthesis of rodlike ruthenium(II) coordination polymers having metal-nitrogen and metal-carbon bonds in their main chains

“…However, it is of interest to also make these polymers B available because (i) they should show electronic and optical properties quite different from those of polymers A, (ii) their chains should have a more pronounced covalent character and should be even more stable than chains A, and (iii) they have a lower or even vanishing ionic charge density, giving rise to clearly different properties in bulk and solution compared to systems like A. Recently, Constable, Sauvage and others developed synthetic methods which open up access to low-molecular-weight octahedral ruthenium(II)-polyimine complexes in which one carbon atom acts as a ligand in addition to five nitrogen atoms [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Provided it is possible to increase the efficiency of the complex-formation processes, it should be possible to also take advantage of these procedures for the successful preparation of multinuclear and thus polymeric coordination compounds.…”