Tunable and Efficient White Light Phosphorescent Emission Based on Single Component N-Heterocyclic Carbene Platinum(II) Complexes

Abstract

A new class of cyclometalated pyridine N-heterocyclic carbene (NHC) Pt(II) complexes with electronically different alkyne derivatives (C≡CR; R = C6H4C(CH3)3 (1), C6H5 (2), C6H4F (3), C6H3(CF3)2 (4)) as ancillary ligands were synthesized, and the consequences of the electronic properties of the different substituted phenylacetylene ligands on the phosphorescent emission efficiencies were studied, where C≡CC6H4C(CH3)3 = 4-tert-butylphenylacetylene, C≡CC6H5 = phenylacetylene, C≡CC6H4F = 4-fluorophenylacetylene, and C≡CC6H3(CF3)2 = 3,5-bis(trifluoromethyl)phenylacetylene. Structural characterization, electrochemistry, and photophysical investigations were performed for all four compounds. Moreover, the emission quantum efficiencies and wavelength emission intensities of the complexes were also recorded in different weight percents in poly(methyl methacrylate) films (PMMA) and evaluated in the CIE-1931 chromaticity diagram. The square planar coordination geometry with the alkynyl ligands was corroborated for complexes 1, 2, and 3 by single crystal X-ray diffraction studies. These complexes show tunable monomeric high energy triplet emission and an additional concentration-dependent low-energy excimer-based phosphorescence. While adopting weight percent concentrations between 15 and 25%, the two emission bands covering the entire visible spectrum were obtained with these particular complexes displaying the properties of an efficient white light triplet emitter with excellent CIE-1931 coordinates (0.31, 0.33). On the basis of the high luminescent quantum efficiency of over 50% for white light emission, these compounds could be potentially useful for white organic light-emitting diodes (WOLEDs) based applications.

Single‐Molecular White‐Light Emitters and Their Potential WOLED Applications

“…It reveals that at the concentration of 20 wt% in poly(methyl methacrylate) (PMMA), both complexes 37 and 38 possess the CIE coordinates close to the pure white light (x = 0.33, y = 0.33). [89] Like the Pt(II) complexes, the gold(I)···gold(I) (Au(I)···Au(I)) interaction to achieve the white-light emission is possible due to the strong tendency to form the excimer, which is supported by the rigid planar configuration and linear coordination mode of Au(I) complexes. [90,91] In 2013, Li et al reported a trinuclear Au(I) cluster 40 which shows a clear dual emission at around 450 nm of the HE side and 560 nm of the LE side in degassed CH 2 Cl 2 at a concentration of 10 −3 m, with the CIE coordinates of (x = 0.28, y = 0.29) and a quantum yield of 25.9%.…”

“…The white emissions are due to the blue emissions at around 460–490 nm from Pt(II) monomers and the excimeric emissions at about 580 nm due to MMLCT with the increased Pt(II) concentration in films. It reveals that at the concentration of 20 wt% in poly(methyl methacrylate) (PMMA), both complexes 37 and 38 possess the CIE coordinates close to the pure white light ( x = 0.33, y = 0.33) …”

Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

“…[6][7][8] Currently, most blue-emitting materials with high quantum yield are based on Ir(III) as the 1 metal ion, but the number of Pt(II) compounds is increasingly growing. 3,[9][10][11][12][13][14][15][16] Population of a high energy excited state required for an efficient blue emission upon excitation competes with the photo-or thermal population of high-lying metal dd* states, the later leading to severe geometrical distortions of the molecules which result in non-radiative deactivation and degradation via bond-breaking processes. 17 In the chemistry of Pt(II), a common approach for the design of efficient and stable blue-phosphorescent systems is the incorporation of strong field 7 ligands to the metal coordination sphere, such as C-deprotonated imines able to act as 8 bidentate, 18,19 tridentate 11,17,20 and even tetradentate [21][22][23][24] ligands.…”

Luminescent properties of a polymeric copper(I)-bromide complex in a PMMA film

“…However, the luminescent properties might be changed by making the film depending on the complexes. 27,28) Therefore, it is desirable to develop a copper(I)-halide complex, in which the original luminescent properties of the powder are retained even in film state. Among the polymers used as binding agents, polymethyl methacrylate (PMMA) is preferred, because it is highly transparent, light-resistant, and easily forms a thin film.…”