ABSTRACT
The orientation of facial (fac) tris-cyclometalated iridium complexes in doped films prepared by vacuum deposition is investigated by altering the physical shape and electronic asymmetry in the molecular structure. Angle-dependent photoluminescence spectroscopy and Fourier-plane imaging microscopy show that the orientation of roughly spherical fac-tris(2-phenylpyridyl)iridium (Ir(ppy)3 ) is isotropic, whereas complexes that are oblate spheroids, fac-tris(mesityl-2-phenyl-1H-imidazole)iridium (Ir(mi)3 ) and fac-tris((3,5-dimethyl-[1,1'-biphenyl]-4-yl)-2-phenyl-1H-imidazole)iridium (Ir(mip)3 ), have a net horizontal alignment of their transition dipole moments. Optical anisotropy factors of 0.26 and 0.15, respectively, are obtained from the latter complexes when doped into tris(4-(9H-carbazol-9-yl)phenyl)amine host thin films. The horizontal alignment is attributed to the favorable van der Waals interaction between the oblate Ir complexes and host material. Trifluoromethyl groups substituted on one polar face of the Ir(ppy)3 and Ir(mi)3 complexes introduce chemical asymmetries in the molecules at the expense of their oblate shapes. The anisotropy factors of films doped with these substituted derivatives are lower relative to the parent complexes, indicating that the fluorinated patches reinforce horizontal alignment during deposition. High efficiencies obtained from organic light emitting diodes prepared using the Ir dopants is attributed, in part, to improved outcoupling of electroluminescence brought about by molecular alignment.
ABSTRACT
Boron dipyrromethene (BODIPY) derivatives have found widespread utility as chromophores in fluorescent applications, but little is known about the photophysical properties of pyridine-based BODIPY analogues, dipyridylmethene dyes. Indeed, it has been reported that boron difluoride dipyridylmethene (DIPYR) is nonemissive, and that derivatives of DIPYR have modest, if any, luminescence. In this report, we explore this little-touched area of chemical space and investigate the photophysical properties of three simple DIPYR dyes: boron dipyridylmethene, boron diquinolylmethene, and boron diisoquinolylmethene. The three dyes strongly absorb in the blue-green part of the spectrum (λem = 450-520 nm, ε = 2.9-11 × 104 M-1 cm-1) and display green fluorescence with high quantum yields (ΦPL = 0.2, 0.8, and 0.8, respectively). Key photophysical properties in these systems were evaluated using a combination of TD-DFT and extended multiconfigurational quasidegenerate second-order perturbation theory (XMCQDPT2) methods and compared to experimental results, revealing that high quantum yields of the quinoline and isoquinoline derivatives are a result of the relative reordering of S1 and T2 state energies upon benzannulation of the parent structure. The intense absorption and high emission efficiency of the benzannulated derivatives make these compounds an intriguing class of dyes for further derivatization.
ABSTRACT
Synthesis, structural and characterization data are provided for Pt(II) and Ir(III) complexes cyclometalated with 2-(corannulene)pyridine (corpy), (corpy)Pt(dpm) and (corpy)Ir(ppz)2 (dpm = dipivaloylmethanato, ppz = 1-phenylpyrazolyl). A third compound, (phenpy)Ir(ppz)2 (phenpy = 2-(5-phenanthryl)pyridyl), was also prepared to mimic the steric bulk of (corpy)Ir(ppz)2. X-ray analysis reveals bowl depths of 0.895 Å for (corpy)Pt(dpm) and 0.837 Å in (corpy)Ir(ppz)2. Neither complex displayed bowl-to-bowl stacking in the crystal lattice. A fluxional process for (corpy)Ir(ppz)2 attributed to bowl inversion of corrannulene is observed in solution with a barrier (ΔG() = 13 kcal mol(-1)) and rate (k = 2.5 × 10(3) s(-1)) as determined using variable temperature (1)H NMR spectroscopy. All of the complexes display red phosphorescence at room temperature with quantum yields of 0.05 in solution and 0.2 in polymethyl methacrylate (PMMA).
