Syntheses, photoluminescence and electroluminescence of some new blue-emitting phosphorescent iridium(III)-based materials

Abstract

The cyclometallated ligand 2-(4',6-difluorophenyl)-4-methoxypyridine (F(2)MeOppyH), whose complexes with iridium(III) emit bright blue to green light, was synthesized in five separate steps. Ir(F(2)MeOppy)(2)(acac), (acacH = 2,4-pentanedione), Ir(F(2)MeOppy)(2)(pic) (picH = 2-picolinic acid), fac-Ir(F(2)MeOppy)(3) and mer-lr(F(2)MeOppy)(3) complexes were synthesized from solution and fully characterized. The structures of Ir(F(2)MeOppy)(2)(acac) and fac-Ir(F(2)MeOppy)(3) were authenticated by X-ray single crystal structure analysis. fec-Ir(F(2)MeOppy)(3) showed a much higher solution photoluminescence (PL) quantum efficiency and blue-shifted emission compared to its counter mer-isomer. All of the complexes showed reversible oxidations between 0.3 and 0.7 V versus the ferrocene/ferrocenium ion. The relative thermodynamic stability of the mer versus fac isomer was investigated and correlated to their corresponding redox and PL properties. Two electroluminescent (EL) devices (D-1 and D-2) were fabricated using the same blue Ir(F(2)MeOppy)(2)(acac) complex as a a dopant but with two different hole blockers, BCP and BAlq, and consequently BCP proved itself a good hole blocker for this type of system. The fabrication of another EL device (D-3) was carried out by using the same dopant, only replacing the host CBP by a wider band gap host, mCP which showed improved luminance, luminance yield and power efficiency (D-2: 133 cd m(-2) 0.66 cd A(-1), 0.22 lm W-1; D-3: 326 cd m(-2); 1.63 cd A(-1); 0.26 lm W-1). (C) 2004 Elsevier Ltd. All rights reserved.