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Abstract: New cyclometalated Iridium (III) complexes of 4-naphthalen-1-yl-2-phenyl-pyridine and 5-naphthalene-1-yl-2-phenylpyridine were synthesized and characterized. Substitution on the pyridine ring of C⋁N ligands was used to alter the electronic properties of these complexes. The (C⋁N)^sub 2^Ir(µ-Cl^sub 2^)Ir(C⋁N)^sub 2^ complexes show phosphorescence with good quantum yields and the emission of these complexes were 530-531 nm. All the ligands and complexes were characterized by ^sup 1^H, ^sup 13^C NMR, MALDI-MS and CHN analysis.
Keywords: Cyclometalated Ir(III), Triplet state, Yellow phosphorescence, Organic emitting materials.
Introduction
In recent decades, intense research activities have been undertaken on organic light-emitting diodes (OLEDs) because of their extremely high efficiency as electroluminescent emitters. [1-3]
Electrophosphorescent materials such as iridium, platinum and ruthenium complexes, which use both singlet and triplet excitation have received a great deal of attention.[5-8] The complexes of these heavy metals mainly include square planar d8 or octahedral d6 and are known to induce intersystem crossing by strong spin-orbit coupling, leading to mixing of the singlet and triplet excited states.[9,10] Iridium complexes have been regarded as the most appropriate phosphorescent materials because of their relatively short lifetime, which minimizes annihilation of triplet emissive states, high quantum efficiency and good stability[11].
In literature, several cyclometalating ligands have been employed with Ir(III) complexes, such as 2,3-diphenyl-quinoxaline, 2-quinolinylpyridine, 2-thienylpyridine and 2-benzothienylpyridine[12,13].
2-Phenylpyridine derivatives were used extensively with Ir(III) complexes[14,15]. Here, we are synthesizing and studying the photophysical properties of bridged cyclometalated Ir(III) complexes by using modified 2-phenylpyridine as ligand, which is substituted in the pyridine ring rather than the phenyl ring Scheme 1.
Results and Discussion
The ligands 4-naphthalen-1-yl-2-phenyl-pyridine (1A) and 5- naphthalene-1-yl-2-phenyl-pyridine (1B) were synthesized as shown in Scheme 1.[16, 17] To a solution of 2-phenylpyridne and B2pin2 (pin = O2C6H12) in hexane, 2.5 mol% of [Ir(COD)(μ-OMe)]2 and 5 mol% of 4,4'-di-tert-butyl-[2,2']bipyridinyl (dtbpy) were added and stirring at room temperature. After 16 h, in situ GC/MS analysis of the reaction mixture showed borylation of 2-phenypyridine giving rise to equal amounts of 2-Ph-4-(Bpin)-pyridine and 2-Ph-5-(Bpin)-pyridine with 90% conversion. Followed by Suzuki-Miyaura cross-coupling reaction,[18,19] 20 ml of 1,4-dioxane was added to the crude mixture and 2 equiv. of aq. K2CO3 in the presence of 5 mol% [Pd(PPh3)2Cl2]. This mixture heated to 80 °C for 16 h under nitrogen. The product was extracted with ethylacetate,...