Synthesis and photophysical properties of bis-cyclometallated iridium(III)-styryl complexes and their saturated analogues

This manuscript reports the synthesis and photophysical investigation of a series of Ir^III complexes Ir(C∧N)₂(O∧O) which are functionalized in the para position of the pyridine ring by styryl groups substituted with electron-donor and -acceptor end groups. The saturated derivative Ir(C∧N-ppy-4-CH₂CH₂C₆H ₄OMe)₂(O∧O-acac) (4a-H₂) was formed from [Ir(C∧N-ppy-4-CH=CHC₆H₄OMe)₂] ₂(μ-Cl)₂ (3a) at 140°C, whereas at 80°C the parent unsaturated complexes Ir(C∧N-ppy-4-CH=CHC₆H ₄R)₂(O∧O) [O∧O = acac, R = OMe (4a), NEt ₂ (4b), H (4c), NO₂ (4d); O∧O = dpm, R = OMe (5a), NEt₂ (5b)] were isolated. The saturated complex 4a-H₂ exhibits intense green emission with a 36 % quantum yield at 298 K. The styryl complexes 4a 4d, 5a and 5b are very weakly emissive at 298 K, but show intense red luminescence in alcohol glass at 77 K. The amino- and nitro-substituted complexes 4b and 4d give low-energy emission (λ_em = 651 and 647 nm, respectively). The emissive states of these complexes are believed to possess predominant triplet intra-ligand charge-transfer (³ILCT) and metal-to-ligand charge-transfer (³MLCT) character, respectively. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.