Abstract
Biscyclometallated iridium complexes [Ir(ppz)2(X^Y)][PF6] (X^Y = pyridine imine) have been synthesised. The pyridineimine ligands are prepared in situ during the complexation. The complexes show room temperature emission between 640 and 780 nm in CH2Cl2 solution. The emission is red shifted compared with the analogous bipyridine complex [Ir(ppz)2(bipy)][PF6]. DFT calculations have been used to shed light on the influence of the imine substituent on the electrochemical and photochemical properties. In particular, the calculations suggests that there is a significant change in geometry between the ground state and the first triplet excited state for arylimines but not for alkylimines, leading to much weaker emission for the arylimine complexes. The work demonstrates that pyridineimines can be used as a substitute for bipyridines in luminescent iridium complexes.
Highlights
Following the report by Thompson et al in 19991 of an OLED containing cyclometalated iridium complex [Ir( ppy)3] (Hppy = 2-phenylpyridine) as a dopant there has been a huge upsurge of interest in complexes [Ir(C^N)3] and [Ir(C^N)2(X^Y)]
Our first attempts at preparation involved synthesis of the pyridine imine ligand followed by complexation with the appropriate [Ir(C^N)2Cl]2 dimer
The reactions of dimers 3a–c with pyridine-2-carboxaldehyde and the relevant amine and KPF6 were carried out in methanol at 60 °C under microwave irradiation for 20 min, to form compounds 4a–c, 5a– 9a in good (>80%) yields (Scheme 1). In these reactions it is not known whether the free pyridineimine ligands are generated in situ or they are formed after coordination of pyridine-2
Summary
Following the report by Thompson et al in 19991 of an OLED containing cyclometalated iridium complex [Ir( ppy)3] (Hppy = 2-phenylpyridine) as a dopant there has been a huge upsurge of interest in complexes [Ir(C^N)3] and [Ir(C^N)2(X^Y)]. Cationic complexes [Ir(C^N)2(X^Y)]+ have also been used in light emitting electrochemical cells.[2] The luminescence of these complexes can be tuned by altering the heterocycle, the degree of conjugation in the C^N ligand and/or the ancillary ligand and by the use of substituents on the cyclometalated phenyl, the directing heterocycle or the ancillary ligands or indeed combinations of these.[3] In cationic complexes [Ir(C^N)2(X^Y)]+ the X^Y ligand has been usually a bipyridine or phenanthroline or substituted derivative, with some examples of pyridine imidazoles,[4] pyridine pyrazoles,[5] and pyridine triazoles.[6] However, changing substituents on a bipyridine is time-consuming from a synthetic viewpoint, hence, finding an alternative to bipyridine ligands that can be easily modified may expand the usefulness of these complexes. Pyridineimines are
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