Theoretical Studies of Blue-Emitting Iridium Complexes with Different Ancillary Ligands

Abstract

The structural and electronic properties of two heteroleptic iridium complexes Ir(dfppy)2(pic) (FIrpic) and Ir(dfppy)2(acac) (FIracac) have been investigated theoretically, where dfppy = 2-(2,4-difluorophenyl) pyridine, pic = picolinic acid, and acac = acetoylacetonate. The geometries of ground and excited states are optimized at PBE0/LANL2DZ and CIS/LANL2DZ levels, respectively. Time-dependent density functional theory (TDDFT) method is employed to explore the absorption and emission properties. In the ground state, the highest-occupied molecular orbital has a significant mixture of metal Ir(d) and dfppy(pi), the lowest-unoccupied orbital locates primarily on pi* of pic for FIrpic and pi* of dfppy for FIracac. The luminescence of each complex originates from the lowest triplet excited state, which is assigned to the mixing of metal-to-ligand charge transfer and intraligand charge transfer characters. The effects of ancillary ligands pic and acac on absorption and emission spectra are observed by analysis of TDDFT results. The connection between the nature of excited states and the behavior of the complexes with different ancillary ligands is elucidated.

Tuning the Emission Color of Iridium(III) Complexes with Ancillary Ligands: A Combined Experimental and Theoretical Study

“…The calculated bond lengths are in good agreement with available crystal structural data (standard deviation of about 0.0038 Å) [20] and are comparable with previously calculated results. [16,21] The calculated metal-ligand Ir-C (about 2.002 Å) and Ir-N (about 2.064 Å) bond lengths in all three complexes are almost the same, whereas the Ir-O bond lengths vary slightly as the ancillary ligands change. The phenyl group in dbm exhibits a stronger conjugating effect on the C=O bond than the methyl group in acac, thus leading to higher electron density on the oxygen atom and a shorter Ir-O bond.…”

“…The effect of the strong π-electron delocalization of [a] Values in parentheses are from ref. [16] .…”

“…Likewise, spectroscopic studies have revealed that ancillary ligands alter the 1 MLCT energy by changing the HOMO energy level, [15] and theoretical calculations have indicated that strong-field ancillary L ∧ X ligands lengthen the bonds between the C ∧ N ligands and the metal, thus altering the electronic properties of the metal complexes. [16] Research on ancillary ligands has therefore attracted more and more attention.…”

Charge-transfer complexes of iodoform with 1,4-dioxane, -dithiane, and -diselenane: Theoretical electron density and energy decomposition analysis

“…All the calculated q cp are much less than 0:5 eÅ À3 , and r 2 q cp are more than zero, indicating that there exists intermolecular noncovalent interaction. Compared with the experimental value of q cp and r 2 q cp , the PBE0 gives better results than other methods, probably because PBE0 is more suitable to study the structures with charge-transfer nature, such as metal complexes, in which there exists charge transfer from metal to ligand [57]. Considering the accuracy of the geometrical structure and topological properties of electron density, the PBE0 method was chosen to study the rest of complexes.…”

Theoretical study on the influence of ancillary ligand on the energy and optical properties of heteroleptic phosphorescent Ir(III) complexes

“…However, the synthesis of an electrophosphorescent iridium complex forming the newly synthesized cyclometalating ligand (C^N) is not always feasible because the chloride-bridged iridium dimmer intermediate, (C^N) 2 Ir(m-Cl) 2 Ir(C^N) 2 , is often difficult to prepare for steric and electronic reasons [12]; so most of the groups have demonstrated tuning of the phosphorescence wavelength from blue to red with the most common strategy adjusting various electron-donating or electron-withdrawing substituents at different positions of the coordinated ligands [13][14][15][16][17][18][19]. While Park and co-workers have demonstrated the full potential of a color tuning methodology with an ancillary ligand and suggested its most probable mechanism in hetreroleptic iridium complexes [12], Gu et al [20] have done a theoretical study of complex FIrpic. In the present study, to provide an in-depth theoretical understanding of the relationship between the electronic structures of different ancillary ligands and spectroscopic properties of these Ir(III) complexes, the theoretical calculations on these four molecules selected from the system, which were synthesized by Park et al including FIrpic, FIrmpic, FIrpca, and FIrprza were performed.…”