Cross-couplings in the elaboration of luminescent bis-terpyridyl iridium complexes: the effect of extended or inhibited conjugation on emission.
The utility of Suzuki cross-coupling methodology for the in situ elaboration of bromo-functionalised bis-terpyridyl iridium(III) complexes has been explored. The complex [Ir(tpy)(tpy-phi-Br)]3+ [tpy-phi-Br = 4'-(4-bromophenyl)-2,2':6',2''-terpyridine] undergoes palladium-catalysed cross-coupling with aryl boronic acids to yield biaryl-substituted complexes directly. The biphenyl and 4-cyanobiphenyl-substituted products display relatively intense, long-lived (tau > 100 mus) yellow emission in degassed aqueous solution at room temperature, assigned to a 3pi-pi* state. A 4-aminobiphenyl-substituted analogue displays an additional low energy absorbance band, attributed to an intraligand charge-transfer (ILCT) excited state, and is scarcely emissive under the same conditions. The iridium(III) complex of 4'-mesityl-terpyridine is also reported. Its emission is much shorter-lived, with a spectral profile resembling that of unsubstituted [Ir(tpy)2]3+, confirming the need for the attainment of a roughly coplanar geometry for stabilisation of the 3pi-pi* excited state.
Leslie
Wendy
W
Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE.
Batsanov
Andrei S
AS
Howard
Judith A K
JA
Williams
J A Gareth
JA
D000042:Absorption; D018360:Crystallography, X-Ray; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry; D007495:Iridium / Q000737:chemistry*; D049449:Luminescence; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
D006575:Heterocyclic Compounds, 3-Ring; D009942:Organometallic Compounds; D011725:Pyridines; D007495:Iridium