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Orange and Red Organic Light‐Emitting Devices Employing Neutral Ru( II ) Emitters: Rational Design and Prospects for Color Tuning
Author(s) -
Tung Y.L.,
Chen L.S.,
Chi Y.,
Chou P.T.,
Cheng Y.M.,
Li E. Y.,
Lee G.H.,
Shu C.F.,
Wu F.I.,
Carty A. J.
Publication year - 2006
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200500901
Subject(s) - quantum efficiency , materials science , trifluoromethyl , electroluminescence , dopant , density functional theory , oled , phosphorescence , homo/lumo , time dependent density functional theory , biphenyl , pedot:pss , luminous efficacy , styrene , indium tin oxide , doping , photochemistry , chemistry , optoelectronics , molecule , thin film , nanotechnology , layer (electronics) , computational chemistry , organic chemistry , optics , physics , polymer , alkyl , copolymer , composite material , fluorescence
A new series of charge‐neutral Ru( II ) pyridyl and isoquinoline pyrazolate complexes, [Ru(bppz) 2 (PPh 2 Me) 2 ] (bbpz: 3‐ tert ‐butyl‐5‐pyridyl pyrazolate) ( 1 ), [Ru(fppz) 2 (PPh 2 Me) 2 ] (fppz: 3‐trifluoromethyl‐5‐pyridyl pyrazolate) ( 2 ), [Ru(ibpz) 2 (PPhMe 2 ) 2 ] (ibpz: 3‐ tert ‐butyl‐5‐(1‐isoquinolyl) pyrazolate) ( 3 ), [Ru(ibpz) 2 (PPh 2 Me) 2 ] ( 4 ), [Ru(ifpz) 2 (PPh 2 Me) 2 ] (ifpz: 3‐trifluoromethyl‐5‐(1‐isoquinolyl) pyrazolate) ( 5 ), [Ru(ibpz) 2 (dpp)] (dpp represents cis ‐1,2‐bis‐(diphenylphosphino)ethene) ( 6 ), and [Ru(ifpz) 2 (dpp)] ( 7 ), have been synthesized, and their structural, electrochemical, and photophysical properties have been characterized. A comprehensive time‐dependant density functional theory (TDDFT) approach has been used to assign the observed electronic transitions to specific frontier orbital configurations. A multilayer organic light‐emitting device (OLED) using 24 wt % of 5 as the dopant emitter in a 4,4′‐ N , N ′‐dicarbazolyl‐1,1′‐biphenyl (CBP) host with 4,4′‐bis[ N ‐(1‐naphthyl)‐ N ‐phenylamino]biphenyl (NPB) as the hole‐transport layer exhibits saturated red emission with an external quantum efficiency (EQE) of 5.10 %, luminous efficiency of 5.74 cd A –1 , and power efficiency of 2.62 lm W –1 . The incorporation of a thin layer of poly(styrene sulfonate)‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT) between indium tin oxide (ITO) and NPB gave anoptimized device with an EQE of 7.03 %, luminous efficiency of 8.02 cd A –1 , and power efficiency of 2.74 lm W –1 at 20 mA cm –2 . These values represent a breakthrough in the field of OLEDs using less expensive Ru( II ) metal complexes. The nonionic nature of the complexes as well as their high emission quantum efficiencies and short radiative lifetimes are believed to be the key factors enabling this unprecedented achievement. The prospects for color tuning based on Ru( II ) complexes are also discussed in light of some theoretical calculations.