Abstract
A cyclometalated iridium complex is reported where the core complex comprises naphthylpyridine as the main ligand and the ancillary 2,2′-bipyridine ligand is attached to a pyrene unit by a short alkyl bridge. To obtain the complex with satisfactory purity, it was necessary to modify the standard synthesis (direct reaction of the ancillary ligand with the chloro-bridged iridium dimer) to a method harnessing an intermediate tetramethylheptanolate-based complex, which was subjected to acid-promoted removal of the ancillary ligand and subsequent complexation. The photophysical behavior of the bichromophoric complex and a model complex without the pendant pyrene were studied using steady-state and time-resolved spectroscopies. Reversible electronic energy transfer (REET) is demonstrated, uniquely with an emissive cyclometalated iridium center and an adjacent organic chromophore. After excited-state equilibration is established (5 ns) as a result of REET, extremely long luminescence lifetimes of up to 225 μs result, compared to 8.3 μs for the model complex, without diminishing the emission quantum yield. As a result, remarkably high oxygen sensitivity is observed in both solution and polymeric matrices.
Highlights
Essential properties of transition metal complexes that are intimately linked to the electronic and steric aspects of ligands in the primary coordination sphere include redox properties, light absorption, and emission
Here we report a straightforward structural modification of a cyclometalated iridium complex, involving the judicious integration of an auxiliary matched organic chromophore, in order to obtain a much longer lived luminescent complex (2), while retaining a similar emission quantum yield
Naphthlypyridine based cyclometalated iridium complexes display 3MLCT based emission centered around 600 nm, which can be fine tuned depending on the coligands present in the primary coordina tion sphere.[10,11]
Summary
Essential properties of transition metal complexes that are intimately linked to the electronic and steric aspects of ligands in the primary coordination sphere include redox properties, light absorption, and emission. Emission quantum yields (Φ) of the complexes were determined upon comparison with an optically dilute [Ru(bpy)3]Cl2 standard (Φr) in air equilibrated water (Φ = 0.028)[6] according to the equation Φ = Φr(I/Ir)(Ar/A)(η2/ηr2), where r refers to the reference sample, I is the integrated emission intensity, A is the absorbance at the excitation wavelength, and η is the refractive index of the solvent.
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