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High-Triplet-Energy Dendrons: Enhancing the Luminescence of Deep Blue Phosphorescent lridium(lll) Complexes.

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Title: High-Triplet-Energy Dendrons: Enhancing the Luminescence of Deep Blue Phosphorescent lridium(lll) Complexes.
Authors: Lo, Shih-Chun1, Harding, Ruth E.2, ShipIey, Christopher P.3, Stevenson, Stuart G.2, Burn, Paul L.1 p.burn2@uq.edu.au, SamueI, Ifor D. W.2 dws@st-andrews.ac.uk
Source: Journal of the American Chemical Society. 11/25/2009, Vol. 131 Issue 46, p16681-16688. 8p. 1 Chart, 7 Graphs.
Subjects: Iridium, Dendrimers, Glass transition temperature, Photoluminescence, Light emitting diodes, Quantum chemistry, Quantum efficiency, Electron transport
Abstract: Solution-processable blue phosphorescent emitters with high luminescence efficiency are highly desirable for large-area displays and lighting applications. This report shows that when a fac-tris[1 -methyl- 5-(4-fluorophenyl)-3-n-propyl-1 H-[1 ,2,4]triazoly!]iridium(lll) complex core is encapsulated by rigid high-triplet- energy dendrons, both the physical and photophysical properties can be optimized. The high-triplet-energy and rigid dendrons were composed of twisted biphenyl dendrons with the twisting arising from the use of tetrasubstituted branching phenyl rings. The blue phosphorescent dendrimer was synthesized using a convergent approach and was found to be solution-processable and to possess a high glass transition temperature of 148 °C. The dendrimer had an exceptionally high solution photoluminescence quantum yield (PLOY) of 94%, which was more than three times that of the simple parent core complex (27%). The rigid and high-triplet-energy dendrons were also found to control the intermolecular interactions that lead to the quenching of the luminescence in the solid state, and the film PLOY was found to be 60% with the emission having Commission Internationale de l'Eclairage coordinates of (0.16, 0.16). The results demonstrate that dendronization of simple chromophores can enhance their properties. Single layer neat dendrimer organic light-emitting diodes (OLEDs) had an external quantum efficiency (EQE) of 0.4% at 100 cd/m2. Bilayer devices with an electron transport layer gave improved EQEs of up to 3.9%. Time-resolved luminescence measurements suggest that quenching of triplets by the electron transport layer used in the bilayer OLEDs limits performance. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:Solution-processable blue phosphorescent emitters with high luminescence efficiency are highly desirable for large-area displays and lighting applications. This report shows that when a fac-tris[1 -methyl- 5-(4-fluorophenyl)-3-n-propyl-1 H-[1 ,2,4]triazoly!]iridium(lll) complex core is encapsulated by rigid high-triplet- energy dendrons, both the physical and photophysical properties can be optimized. The high-triplet-energy and rigid dendrons were composed of twisted biphenyl dendrons with the twisting arising from the use of tetrasubstituted branching phenyl rings. The blue phosphorescent dendrimer was synthesized using a convergent approach and was found to be solution-processable and to possess a high glass transition temperature of 148 °C. The dendrimer had an exceptionally high solution photoluminescence quantum yield (PLOY) of 94%, which was more than three times that of the simple parent core complex (27%). The rigid and high-triplet-energy dendrons were also found to control the intermolecular interactions that lead to the quenching of the luminescence in the solid state, and the film PLOY was found to be 60% with the emission having Commission Internationale de l'Eclairage coordinates of (0.16, 0.16). The results demonstrate that dendronization of simple chromophores can enhance their properties. Single layer neat dendrimer organic light-emitting diodes (OLEDs) had an external quantum efficiency (EQE) of 0.4% at 100 cd/m2. Bilayer devices with an electron transport layer gave improved EQEs of up to 3.9%. Time-resolved luminescence measurements suggest that quenching of triplets by the electron transport layer used in the bilayer OLEDs limits performance. [ABSTRACT FROM AUTHOR]
ISSN:00027863
DOI:10.1021/ja903157e