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

Abstract

The cyclometallated ligand 2-(4′,6-difluorophenyl)-4-methoxypyridine (F2MeOppyH), whose complexes with iridium(III) emit bright blue to green light, was synthesized in five separate steps. Ir(F2MeOppy)2(acac), (acacH = 2,4-pentanedione), Ir(F2MeOppy)2(pic) (picH = 2-picolinic acid), fac-Ir(F2MeOppy)3 and mer-Ir(F2MeOppy)3 complexes were synthesized from solution and fully characterized. The structures of Ir(F2MeOppy)2(acac) and fac-Ir(F2MeOppy)3 were authenticated by X-ray single crystal structure analysis. fac-Ir(F2MeOppy)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(F2MeOppy)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).