Dileep A. K. Vezzu

Improvement in phosphorescence efficiency through tuning of coordination geometry of tridentate cyclometalated platinum(II) complexes.

A series of tridentate cyclometalated platinum(II) complexes (C(∧)N*N)PtL (L = Cl or acetylide) featuring a fused five-six-membered metallacycle were synthesized. The structure of the complexes was confirmed by X-ray crystallography. In contrast to the C(∧)N(∧)N platinum complexes with a fused five-five-membered metallacycle, the platinum coordination in C(∧)N*N complexes is much closer to a square planar geometry. The photophysical properties of the complexes were studied. The geometrical change from C(∧)N(∧)N to C(∧)N*N led to a substantial improvement in phosphorescence efficiency of the complexes with an acetylide ligand in solution at room temperature. For example, the quantum yield of (C(∧)N*N)PtCCPh was measured to be 56%, demonstrating a big jump from 4% reported for (C(∧)N(∧)N)PtCCPh.

Highly luminescent tridentate N^C*N platinum(II) complexes featured in fused five-six-membered metallacycle and diminishing concentration quenching.

A series of cyclometalating ligands, N-phenyl-N-(3-(pyridin-2-yl)phenyl)pyridin-2-amine (L1), N-(3-(1H-pyrazol-1-yl)phenyl)-N-phenylpyridin-2-amine (L2), N-phenyl-N-(3-(quinolin-2-yl)phenyl)pyridin-2-amine (L3), N-phenyl-N-(3-(pyridin-2-yl)phenyl)quinolin-2-amine (L4), N-(3-(isoquinolin-1-yl)phenyl)-N-phenylpyridin-2-amine (L5), and N-phenyl-N-(3-(pyridin-2-yl)phenyl)isoquinolin-1-amine (L6), were synthesized, which reacted with K(2)PtCl(4) in glacial acetic acid to produce N^C*N-coordinated platinum(II) complexes featured in a fused five-six-membered metallacycle, 1-6, respectively. The structures of 1, 3, 4, and 6 were determined by single crystal X-ray crystallography. The square geometries of the complexes are improved when compared with those of the N^C^N-coordinated complexes as the bite angles for the platinum in N^C*N-coordinated complexes 1, 3, and 4 are increased. The Pt-C bonds (1.94-1.95 Å) are shorter than those of C^N^N-coordinated platinum complexes but longer than those found for N^C^N-coordinated platinum complexes. With the increase of the steric interaction, the distortion of the molecules from a planar coordination geometry becomes more and more severe from 1 to 3 to 4 and 6, and in 6, the N-phenyl ring has to stand up on the coordination sphere to minimize the steric interaction with the N-isoquinolyl ring. The photophysical properties of the complexes were studied, and their absorption and emission spectra were interpreted by relating to the structural features revealed by the X-ray crystal structures and the orbital characters predicted by DFT calculations. All complexes are emissive in fluid at room temperature, and the quantum yields (up to 0.65) are comparable to those of highly emissive N^C^N-coordinated platinum complexes. Self-quenching was not observed in the concentration range of 10(-6) to 10(-4) M. Large rigidochromic shifts for the emissions of 2, 4, and 6 upon cooling from room temperature to rigid glass (77 K) were observed. Two different triplet states that control the emissions were proposed to account for the photophysical properties of 6.

Acridinone/amine(carbazole)-based bipolar molecules: efficient hosts for fluorescent and phosphorescent emitters.

Three acridinone-based molecules ADBP, ACBP, and DABP were synthesized, and their application to the OLED devices was investigated. When used as the host for either the deep blue singlet or the green triplet emitter in OLED devices, the bipolar molecules ADBP and ACBP demonstrated superior performance compared to either DABP or commonly used host CBP, remarkably lowering the drive voltage and improving efficiencies.