Abstract
We report the spectra of UV-vis absorption, emission and excitation for fluoro-substituted triscarbene iridium complexesfac-tris(1-(4-fluorophenyl)-3- methylimidazolin-2-ylidene-C,C 2 ) iridium(III),fac-Ir(fpmi) 3 , andfac-tris(1-(2, 4-fluorophenyl)-3-methyl imidazolin-2-ylidene-C, C 2 ) iridium(III), fac-Ir(dfpmi) 3 . The decay of emission and transient absorption curves at 266-nm excitation in the singlet metal-to-ligand charge-transfer (MLCT) band region are recorded. Using quantum chemical calculations-density functional theory (DFT) and time-dependent DFT (TD-DFT) method B3LYP, we obtained their optimized geometries, electronic structures, energies of vertical transitions and oscillator strengths. Both complexes emit in deep blue/near UV which has the highest emission energy for iridium complexes. These emission bands display vibronic structure and a small rigidochromic shift in the low-temperature. From the measured lifetime data and the emission quantum yield, we obtain a radiative rate constant k r 2.2-2.4 × 10 4 s- 1 for the emitting state and assign the emitting state to 3 π-π * for these complexes. In subpicosecond transient absorption, we observed an ultrafast rise implying that crossing rate from 1 MLCT to this ligand-centered T1/T2 3 π-π * state is faster than our temporal resolution (300 fs)- 1 . Two components appear with time constants 0.7-1.5 ps and 15-47 ps and are assigned to vibrational cooling/solvation and geometry relaxation, respectively. © 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA.