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Cationic Heteroleptic Cyclometalated Iridium Complexes with 1‐Pyridylimidazo[1,5‐α]pyridine Ligands: Exploitation of an Efficient Intersystem Crossing
Author(s) -
Volpi Giorgio,
Garino Claudio,
Salassa Luca,
Fiedler Jan,
Hardcastle Kenneth I.,
Gobetto Roberto,
Nervi Carlo
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801474
Subject(s) - iridium , phosphorescence , photochemistry , intersystem crossing , chemistry , pyridine , acetonitrile , luminescence , excited state , density functional theory , time dependent density functional theory , ligand (biochemistry) , materials science , fluorescence , computational chemistry , singlet state , catalysis , organic chemistry , physics , optoelectronics , quantum mechanics , nuclear physics , biochemistry , receptor
Luminescent ligands in Ir III cyclometalated complexes. The photophysical and photochemical properties of Ir‐cyclometalated complexes containing luminescent ligands are evaluated (see figure). Significant admixture between Ir and ligand orbitals induces an efficient intersystem crossing. Photochemical reactions performed in the presence of oxygen lead to new Ir‐cyclometalated complexes containing N(amido) groups directly bound to Ir.A series of phosphorescent cyclometalated heteroleptic iridi um(III) phenylpyridinato (ppy) complexes containing luminescent 1‐pyridylimidazo[1,5‐α]pyridine (pip) ligands, namely [Ir(ppy) 2 (pip)] + , have been synthesised, characterised and their electrochemical, photophysical and electronic properties studied. Seven X‐ray structures have been resolved. Excitation of [Ir(ppy) 2 (pip)] + in acetonitrile at room temperature results in a dual luminescence, strongly quenched by O 2 . Four complexes show, in absence of O 2 , a high‐energy emission (assigned to a 3 MLLCT transition) with two maxima in the blue region of the visible spectra, and a second structured emission (assigned largely to a 3 LC π–π* transition) centred around λ =555 nm. Lifetimes of high‐energy emissions are between 0.6 and 1.3 μs. Time‐dependent density functional calculations combined with the conductor‐like polarisable continuum model method, with acetonitrile as solvent, have been used to calculate a series of ground and excited states of the derivatives under investigation, and the transitions compared with the experimental UV/Vis absorption spectra. A quick and efficient photochemical reaction has been observed for these iridium derivatives that leads to the formation of a new class of cyclometalated iridium complexes containing a stable deprotonated amide unusually coordinated to the metal through a nitrogen bond. The synthesis of a 15 N enriched selected ligand has been performed to investigate, by means of NMR, the particular facile route to these new set of derivatives. The electrochemical behaviour of all complexes is also reported.