Synthesis and Luminescence of a Charge-Neutral, Cyclometalated Iridium(III) Complex Containing N∧C∧N- and C∧N∧C-Coordinating Terdentate Ligands

Abstract

The first examples of iridium(III) complexes containing a terdentate, N--C--N-coordinated 1,3-di(2-pyridyl)benzene derivative, cyclometalated at C2 of the benzene ring, are reported. This mode of binding becomes significant only if competitive cyclometalation at C4/C6 is blocked, and the ligand 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyxH) has been prepared to achieve this condition. The charge-neutral complex [Ir(dpyx)(dppy)], 2, (dppyH(2) = 2,6-diphenylpyridine) has been isolated, containing dpyx and dppy bound to the metal through one and two carbon atoms, respectively. A terpyridyl analogue, [Ir(dpyx)(ttpy)](PF(6))(2), 3, (ttpy = 4'-tolylterpyridine) has also been prepared and its X-ray crystal structure determined, confirming the N--C--N binding mode of dpyx. Complex 2 emits strongly in degassed solution at 295 K (lambda(max) = 585 nm, phi = 0.21, tau = 3900 ns, in CH(3)CN). In solution, the excited state can also undergo photodissociation, through cleavage of one of the Ir-C(dppy) bonds.

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[21,70] As introduced by Neve and co-workers, [61,71] the commonly used synthetic protocol towards cationic biscyclometallated iridium(III) polypyridyl complexes is based on a bridge-splitting reaction of the appropriate chloro-bridged iridium dimer complexes under mild conditions. A variety of different 2,2 0 -bipyridine, 1,10-phenanthroline, and 2,2 0 :6 0 ,2 00 -terpyridine derivatives has found use as neutral bidendate ligands.…”

Spectroscopic properties of cyclometallated iridium complexes by TDDFT

“…Ground state DFT calculations have become increasingly popular in conjunction to experimental electrochemical measurements to assign the character of the redox processes involving iridium(III) compounds [10,11,20,[24][25][26][27][28][29][30][31][32], by looking at the HOMO and LUMO localization. Information about the HOMO and LUMO is also often used to estimate the nature of the lowest excited states, assuming a single orbital picture of the electronic transitions.…”

Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their Applications

“…A critical drawback of this approach is that enhanced internal strain may promote nonradiative decay, whereby higher excited-state energy is attained at the expense of other important properties (e.g., luminous intensity and excited-state lifetime). [33][34][35] Alternatively, recent investigations of iridiumA C H T U N G T R E N N U N G (III) complexes involving terdentate cyclometalating ligands (e.g., 2,6-diphenyl-pyridine [36,37] and 1,3-bis-(1-methyl-benzimidazol-2-yl)benzene [38] ) have shown that low-energy emission can be readily achieved in complexes containing ligands with extended p systems. [36][37][38] Another promising method for tuning (and fine-tuning) the excited-state properties of iridiumA C H T U N G T R E N N U N G (III) complexes involves deliberate functionalization of the ligands through the use of substituent groups.…”

“…[33][34][35] Alternatively, recent investigations of iridiumA C H T U N G T R E N N U N G (III) complexes involving terdentate cyclometalating ligands (e.g., 2,6-diphenyl-pyridine [36,37] and 1,3-bis-(1-methyl-benzimidazol-2-yl)benzene [38] ) have shown that low-energy emission can be readily achieved in complexes containing ligands with extended p systems. [36][37][38] Another promising method for tuning (and fine-tuning) the excited-state properties of iridiumA C H T U N G T R E N N U N G (III) complexes involves deliberate functionalization of the ligands through the use of substituent groups. By modifying the symmetry and inductive influence of a ligand with different substituents, it is possible to control metal-ligand bonding as well as ligand orbital energies and, thus, to control the nature of the lowest excited state.…”