Organic element for electroluminescent devices

#This invention relates to organic light emitting diode (OLED) electroluminescent (EL) device comprising a light-emitting layer containing a boron dopant compound containing a bis(azinyl)methene boron group.

#While organic electroluminescent (EL) devices have been known for over two decades, their performance limitations have represented a barrier to many desirable applications. In simplest form, an organic EL device is comprised of an anode for hole injection, a cathode for electron injection, and an organic medium sandwiched between these electrodes to support charge recombination that yields emission of light. These devices are also commonly referred to as organic light-emitting diodes, or OLEDs. Representative of earlier organic EL devices are Gurnee et al. U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No. 3,173,050, issued Mar. 9, 1965; Dresner, “Double Injection Electroluminescence in Anthracene”, RCA Review, Vol. 30, pp. 322-334, 1969; and Dresner U.S. Pat. No. 3,710,167, issued Jan. 9, 1973. The organic layers in these devices, usually composed of a polycyclic aromatic hydrocarbon, were very thick (much greater than 1 μm). Consequently, operating voltages were very high, often >100V.

#More recent organic EL devices include an organic EL element consisting of extremely thin layers (e.g. <1.0 μm) between the anode and the cathode. Herein, the organic EL element encompasses the layers between the anode and cathode electrodes. Reducing the thickness lowered the resistance of the organic layer and has enabled devices that operate at much lower voltage. In a basic two-layer EL device structure, described first in U.S. Pat. No. 4,356,429, one organic layer of the EL element adjacent to the anode is specifically chosen to transport holes, therefore, it is referred to as the hole-transporting layer, and the other organic layer is specifically chosen to transport electrons, referred to as the electron-transporting layer. The interface between the two layers provides an efficient site for the recombination of the injected hole/electron pair and the resultant electroluminescence.

#FIG. 1 shows a cross-section of a typical OLED device in which this invention may be used.

#The invention is generally as described above.

#An OLED device of the invention is a multilayer electroluminescent device comprising a cathode, an anode, charge-injecting layers (if necessary), charge-transporting layers, and a light-emitting layer (LEL) comprising a host and at least one dopant, a bis(azinyl)methene boron compound. The term azine or azinyl refers to a six-membered aromatic ring system containing at least one nitrogen as defined by the Hantzsch-Widman stems [The Naming and Indexing of Chemical Substances for Chemical Abstracts—A Reprint of Index IV (Chemical Substance Index Names) from the Chemical Abstracts—1992 Index Guide; American Chemical Society: Columbus, Ohio, 1992; paragraph 146].

#Suitably, the light-emitting layer of the device comprises a host and dopant where the dopant is present in an amount of up to 10 wt % of the host, more typically from 0.1-5.0 wt % of the host. The group is suitably a 6,6,6-tricyclic bis(azinyl)methene boron complex group, and usefully a bis(pyridinyl)methene boron complex group. Good results are obtained when at least one or both of the pyridyl groups are substituted, particularly where at least one or both of the pyridyl groups has substituent groups joined to form a fused ring.