Qin-De Liu

Diarylamino functionalized pyrene derivatives for use in blue OLEDs and complex formation

Three new 2,2′-dipyridylamino functionalized pyrene derivatives, 1-pyrenyl-2,2′-dipyridylamine (1), 4-(1-pyrenyl)phenyl-2,2′-dipyridylamine (2), and 4-[4′-(1-pyrenyl)biphenyl]-2,2′-dipyridylamine (3) have been synthesized and fully characterized. For comparison of electronic properties, a diphenylamino functionalized molecule 4-[4′-(1-pyrenyl)biphenyl]diphenylamine (4) has also been synthesized. Compounds 1–4 are bright blue emitters in solution and in the solid state with λmax at ∼420–460 nm and a high emission efficiency in solution. All four compounds form amorphous glasses with Tg values of 66 °C, 79 °C, 165 °C, and 98 °C, respectively. The electronic properties of the four compounds were examined by spectroscopic methods, cyclic voltammetry and Gaussian 98 molecular orbital calculations. The utilities of this class of molecules in OLEDs have been demonstrated by EL devices of compounds 3 and 4, which showed that 3 can function as a bright blue emitter and an electron transport material in a double-layer device while 4 can function as a bright blue emitter and a hole transport molecule in a triple-layer device. The dipyridylamino functional group in molecules 1–3 are capable of chelating to metal ions such as Zn(II) as demonstrated by the synthesis and structure of the complex [2·(Zn(O2CCF3)2]2 (5). The binding of Zn(II) ions to the dipyridyl group causes a reduction of the emission efficiency of the ligand 2.

New red–orange phosphorescent/electroluminescent cycloplatinated complexes of 2,6-bis(2′-indolyl)pyridine

Three novel cyclometalated complexes of 2,6-bis(2′-indolyl)pyridine (H2BIP), Pd(BIP)(Py) (Py = pyridine) (1), Pt(BIP)(SMe2) (2) and Pt(BIP)(Py) (3) have been synthesized and characterized structurally. The Pd and Pt centers in these compounds are four-coordinate with a square planar geometry. The BIP ligand acts as a tridentate chelate to the metal center, and the dimethyl sulfide and the pyridine ligand bind to the metal center as terminal ligands. Compound 1 has no luminescence. Compounds 2 and 3 display bright orange luminescence either at 77 K in a frozen CH2Cl2 solution or at ambient temperature in a polymer matrix (e.g. poly(carbonate) or PVK). The emission maxima for 2 and 3 in the frozen CH2Cl2 solution are at λ = 572 and 589 nm, respectively. The emission spectra of 2 and 3 in the polymer matrix are very similar with λmax = 585 nm. The luminescence of 2 and 3 is phosphorescent as supported by the emission lifetimes of 2 (94(1) μs in CH2Cl2 at 77 K, 22.1(1) μs in poly(carbonate) at 298 K) and 3 (44(1) μs in CH2Cl2 at 77 K, 19(1) μs in poly(carbonate) at 298 K). Based on the luminescence properties of the free ligand and the results of molecular orbital calculations, we propose that the luminescence of 2 and 3 is most likely due to a π → π* transition with a significant dπ orbital contribution from the Pt(II) center to the π level. Electroluminescent devices using compound 3 as the emitter and PVK as the host and hole transport material have been fabricated successfully.