Di Girolamo A, Monti F, Mazzanti A, Matteucci E, Armaroli N, Sambri L, Baschieri A. 4-Phenyl-1,2,3-triazoles as Versatile Ligands for Cationic Cyclometalated Iridium(III) Complexes.
Inorg Chem 2022;
61:8509-8520. [PMID:
35609179 PMCID:
PMC9490865 DOI:
10.1021/acs.inorgchem.2c00567]
[Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
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Five cationic iridium(III)
complexes (1–5) were synthesized
exploiting two triazole-based cyclometalating
ligands, namely, 1-methyl-4-phenyl-1H-1,2,3-triazole
(A) and the corresponding mesoionic carbene 1,3-dimethyl-4-phenyl-1H-1,2,3-triazol-5-ylidene (B). From the combination
of these two ligands and the ancillary one, i.e., 4,4′-di-tert-butyl-2,2′-bipyridine (for 1–3) or tert-butyl isocyanide (for 4 and 5), not only the typical bis-heteroleptic complexes
but also the much less explored tris-heteroleptic analogues (2 and 5) could be synthesized. The redox and
emission properties of all of the complexes are effectively fine-tuned
by the different ligands: (i) cyclometalating ligand A induces a stronger highest occupied molecular orbital (HOMO) stabilization
compared to B and leads to complexes with progressively
narrower HOMO–lowest unoccupied molecular orbital (LUMO) and
redox gaps, and lower emission energy; (ii) complexes 1–3, equipped with the bipyridine ancillary ligand,
display fully reversible redox processes and emit from predominantly
metal-to-ligand charge transfer (MLCT) states with high emission quantum
yields, up to 60% in polymeric matrix; (iii) complexes 4 and 5, equipped with high-field isocyanide ligands,
display irreversible redox processes and high-energy emission from
strongly ligand-centered triplets with long emission lifetimes but
relatively low quantum yields (below 6%, both in room-temperature
solution and in solid state). This work demonstrates the versatility
of phenyl-triazole derivatives as cyclometalating ligands with different
chelation modes (i.e., C∧N and C∧C:) for the synthesis of photoactive iridium(III) complexes with
highly tunable properties.
Triazole-based
cyclometalating ligands serving as both standard
C∧N chelators (as in 4-phenyl-triazole) and C∧C: carbene ones (as in 4-phenyl-triazolylidene) have
been used to synthesize a series of cationic iridium(III) complexes.
Accordingly, unusual tris-heteroleptic complexes could be obtained
by simultaneously exploiting both chelation modes. These ligands allow
fine tuning of the properties of the related complexes, which exhibit
luminescence all the way from blue to red and quantum yields up to
60% in a diluted polymeric matrix at 298 K.
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