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Triscyclometalated Iridium(III) Fluoro‐Substituted Carbene Complexes: Character of Emitting Triplet States and Excited State Dynamics
Author(s) -
Chen ChienYu,
Tsai HueiRu,
Lu KunYi,
Yao HusanHsiao,
Yang YuHan Ou,
Cheng ChienHong,
Chen IChia
Publication year - 2013
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.201300161
Subject(s) - chemistry , iridium , excited state , quantum yield , phosphorescence , emission spectrum , density functional theory , ultrafast laser spectroscopy , singlet state , photochemistry , reaction rate constant , atomic physics , analytical chemistry (journal) , spectroscopy , spectral line , fluorescence , computational chemistry , biochemistry , physics , quantum mechanics , astronomy , chromatography , kinetics , catalysis
We report the spectra of UV‐vis absorption, emission and excitation for fluoro‐substituted triscarbene iridium complexes fac ‐tris(1‐(4‐fluorophenyl)‐3‐methylimidazolin‐2‐ylidene‐C,C 2′ ) iridium(III), fac ‐Ir(fpmi) 3 , and fac ‐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 T 1 /T 2 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.