Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes

Abstract

We report new bis-cyclometalated cationic iridium(III) complexes [(C(^)N)(2)Ir(CN-tert-Bu)(2)](CF(3)SO(3)) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or5-trifluoromethyl) as C(^)N ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or blue-green phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-459 nm. The corresponding quantum yields and observed excited-state lifetimes are up to 76% and 46 μs, respectively, and the calculated radiative lifetimes are in the range of 46-82 μs. In solution, the photophysical properties of the complexes are solvent-independent, and their emission color is tuned by variation of the substituents in the cyclometalating ligand. For most of the complexes, an emission color red shift occurs in going from solution to neat solids. However, the shift is minimal for the complexes with bulky tert-butyl or trifluoromethyl groups on the cyclometalating ligands that prevent aggregation. We report the first example of an iridium(III) isocyanide complex that emits blue phosphorescence not only in solution but also as a neat solid.

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

“…If this is the case, as expected from the larger electronegativity of the N atom, the new LUMO is mainly located on the heterocyclic moiety of the (C^N) ligand (e.g., the pyridine ring for ppy-based ligands). In this way, the use of ancillary ligands with relatively inaccessible p* orbitals (e.g., carbenes [85] or isocyanides [92,93] ) leads to low-lying emitting excited states centered on the cyclometalated ligands and the emitting T 1 state exhibits a more ligand-centered character. In such cases, highly structured emissions and strongly increased radiative lifetimes (i.e., small values of k r ) are found.…”

“…The first two examples of this class of complexes were reported by Thompson et Figure 19) has turned out to be first example of an Ir III isocyanide complex whose strong blue phosphorescence is unaffected by passing from solution to the solid state, thanks to the presence of the tertbutyl groups on the ppy ligand that are particularly effective in preventing self-aggregation. [93] In 2007, Chin et al [120] synthesized a series of cationic iridium complexes equipped with even stronger-field ligands, such as CO. Complexes [Ir(ppy) 2 Figure 19) emit at 451-482 nm and 441-443 nm, respectively. Following an analogous approach, Yang et al [85] have recently reported the first LECs based on N-heterocyclic carbene ligands displaying the bluest emission ever reported for a LEC device (456-488 nm).…”

“…[37] Subsequently, the same authors [99] demonstrated that, by extending the intramolecular p-p interactions with a second phenyl group to the 6'-position of the pbpy ligand (complex 32, Figure 25) does not strengthen the intramolecular caging effect because the second p-interaction distorts the planarity of the diimine ligand and enables the population of dissociative 3 MC states. [93] Accordingly, 32 yields less-stable LECs (Table 2).…”

Lumineszierende ionische Übergangsmetallkomplexe für leuchtende elektrochemische Zellen

“…[91] das HOMO aus Ir-dp-Orbitalen (t 2g ) und Phenyl-p-Orbitalen der cyclometallierten C^N-Liganden zusammen, während das LUMO normalerweise am neutralen N^N-Ergänzungsligand lokalisiert ist (Abbildung 16 a). [37] [85] oder Isocyanide [92,93] ) zu tiefer liegenden angeregten Zuständen, die an den cyclometallierten Liganden zentriert sind, und zu einem stärker ligandzentrierten emittierenden T 1 -Zustand. In diesen Fällen beobachtet man stark strukturierte Emissionsbanden und verlängerte Emissionslebensdauern (gleichbedeutend mit kleinen k r -Werten).…”

A Metal-containing Nucleoside That Possesses Both Therapeutic and Diagnostic Activity against Cancer

“…This cyclometalated complex of iridium(III) was chosen due to its high stability in aqueous environments present in a living cell (24). In addition, iridium complexes are high yielding phosphorescent compounds that can be rationally tuned to emit visible light across a range of wavelengths (25). At face value, the size of the iridium complex attached to the deoxyribose moiety appears to be very large and would prohibit its utilization as a substrate for any nucleoside transporter.…”