Pt(II) Metal Complexes Tailored with a Newly Designed Spiro-Arranged Tetradentate Ligand; Harnessing of Charge-Transfer Phosphorescence and Fabrication of Sky Blue and White OLEDs

Tetradentate bis­(pyridyl azolate)
chelates are assembled by connecting two bidentate 3-trifluoromethyl-5-(2-pyridyl)­azoles
at the six position of pyridyl fragment with the tailored spiro-arranged
fluorene and/or acridine functionalities. These new chelates were
then utilized in synthesizing a series of Pt­(II) metal complexes [Pt­(Ln)], n = 1–5, from
respective chelates L1–L5 and [PtCl2(DMSO)2] in 1,2-dimethoxyethane. The single-crystal
X-ray structural analyses were executed on 1, 3, and 5 to reveal the generalized structures and packing
arrangement in crystal lattices. Their photophysical properties were
measured in both solution and solid state and are discussed in the
context of computational analysis. These L1–L5 coordinated Pt­(II) species exhibit intense emission, among
which complex 5 shows remarkable solvatochromic phosphorescence
due to the dominant intraligand charge transfer transition induced
by the new bis­(pyridyl azolate) chelates. Moreover, because of the
higher-lying highest occupied molecular orbital of acridine, complex 5 can be considered as a novel bipolar phosphor. Successful
fabrication of blue and white organic light-emitting diodes (OLEDs)
using Pt­(II) complexes 3 and 5 as the phosphorescent
dopants are reported. In particular, blue OLEDs with 5 demonstrated peak efficiencies of 15.3% (36.3 cd/A, 38.0 lm/W),
and CIE values of (0.190, 0.342) in a double-emitting layer structure.
Furthermore, a red-emitting Os­(II) complex and 5 were
used to fabricate warm-white OLEDs to achieve peak external quantum
efficiency, luminance efficiency, and power efficiency values as high
as 12.7%, 22.5 cd/A, and 22.1 lm/W, respectively.