Three-Coordinate Organoboron Compounds BAr2R (Ar = Mesityl, R = 7-Azaindolyl- or 2,2′-Dipyridylamino-Functionalized Aryl or Thienyl) for Electroluminescent Devices and Supramolecular Assembly

• Published in: Chemistry : a European journal Vol. 10; no. 4; pp. 994 - 1006
• Main Authors: Jia, Wen-Li, Bai, Dong-Ren, McCormick, Theresa, Liu, Qin-De, Motala, Michael, Wang, Rui-Yao, Seward, Corey, Tao, Ye, Wang, Suning
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 20-02-2004; WILEY‐VCH Verlag
• Subjects: blue emitter; boron; coordination chemistry; luminescence; N ligands; OLEDs
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200305579

Eight novel three‐coordinate boron compounds with the general formula BAr2L, in which Ar is mesityl and L is a 7‐azaindolyl‐ or a 2,2′‐dipyridylamino‐functionalized aryl or thienyl ligand, have been synthesized by Suzuki coupling, Ullmann condensation methods, or simple substitution reactions (L = p‐(2,2′‐dipyridylamino)phenyl, 1; p‐(2,2′‐dipyridylamino)biphenyl, 2; p‐(7‐azaindolyl)phenyl, 3; p‐(7‐azaindolyl)biphenyl, 4; 3,5‐bis(2,2′‐dipyridylamino)phenyl, 5; 3,5‐bis(7‐azaindolyl)phenyl, 6; p‐[3,5‐bis(2,2′‐dipyridylamino)phenyl]phenyl, 7; 5‐[p‐(2,2′‐dipyridylamino)phenyl]‐2‐thienyl, 8). The structures of 1, 3, and 5–7 have been determined by X‐ray diffraction analyses. These new boron compounds are bright blue emitters. Electroluminescent devices using compound 2 or 8 as the emitter and the electron‐transport layer have been successfully fabricated. Molecular orbital calculations (Gaussian 98) have established that the blue emission of compounds 1–8 originates from charge transfer between the π orbital of the ligand L and the pπ orbital of the boron center. The ability of these boron compounds to bind to metal centers to form supramolecular assemblies was demonstrated by treatment of compound 2 with Zn(O2CCF3)2, which generated a 1:1 chelate complex {2⋅Zn(O2CCF3)2} (10), and also by treatment of compound 4 with AgNO3, yielding a 2:1 coordination compound {(4)2⋅Ag(NO3)} (11). In the solid state, compounds 10 and 11 form interesting head‐to‐head and tail‐to‐tail extended structures that host solvent molecules such as benzene.
Efficient blue emitters and promising electron‐transport materials for OLEDs are the newly synthesized three‐coordinate boron compounds B(mesityl)2R, in which R is a 7‐azaindolyl‐ or 2,2′‐dipyridylamino‐functionalized aryl group. These compounds are also useful building blocks for supramolecular assembly.