Interplay of Zero-Field Splitting and Excited State Geometry Relaxation in fac-Ir(ppy)₃

Abstract

The lowest energy triplet state, T1, of organometallic complexes based on iridium(III) is of fundamental interest, as the behavior of molecules in this state determines the suitability of the complex for use in many applications, e.g., organic light-emitting diodes. Previous characterization of T1 in fac-Ir(ppy)3 suggests that the trigonal symmetry of the complex is weakly broken in the excited state. Here we report relativistic time dependent density functional calculations of the zero-field splitting (ZFS) of fac-Ir(ppy)3 in the ground state (S0) and lowest energy triplet (T1) geometries and at intermediate geometries. We show that the energy scale of the geometry relaxation in the T1 state is large compared to the ZFS. Thus, the natural analysis of the ZFS and the radiative decay rates, based on the assumption that the structural distortion is a small perturbation, fails dramatically. In contrast, our calculations of these quantities are in good agreement with experiment.

Bond Fission and Non-Radiative Decay in Iridium(III) Complexes

“…Complex 4 with fluorine atoms located on the phenyl ring ortho and para to the triazole of each ligand presents the simplest case. The geometry found for the T1 state at the equilibrium bond length is similar to that found in the S0 state, with some relaxation [11][12][13][14][15] . As the Ir-N1 bond is lengthened there is a single discontinuous change in the energy when it is 0.2-0.3 Å longer than at equilibrium.…”

“…Furthermore, it has been shown that geometry relaxation in the excited state is crucial for understanding the radiative properties of Ir(III) complexes. 11,16,[12][13][14][15] Nevertheless, understanding non-radiative processes in Ir(III) complexes remains a major challenge. But, if one aims to rationally design more efficient blue OLEDs it is the problem that needs to be solved.…”

Effects of steric encumbrance of iridium(iii) complex core on performance of solution-processed organic light emitting diodes

“…36 Previous experimental and theoretical studies of the emissive properties of Ir(ppy) 3 have shown that in experimental setting the C 3 symmetry of the complex is being reduced and the phosphorescence proceeds from C 1 -symmetric excited triplet state, which is localized only on one of the cyclometalating ligands. 33,[36][37][38] The main cause for this process is Jahn-Teller distortion, which lis the energetically unfavorable degeneracy of the long-lived C 3 -symmetric excited state through a transformation of the molecular geometry. [36][37][38] An interaction with surrounding solvent or host matrix molecules is also considered as a possible origin for the loss of the symmetry.…”

“…33,[36][37][38] The main cause for this process is Jahn-Teller distortion, which lis the energetically unfavorable degeneracy of the long-lived C 3 -symmetric excited state through a transformation of the molecular geometry. [36][37][38] An interaction with surrounding solvent or host matrix molecules is also considered as a possible origin for the loss of the symmetry. 33 The aforementioned processes are also expected to take place in the case of the investigated derivatives of Ir(ppy) 3 .…”

Organometallic Coatings for Electroluminescence Applications

“…Some important parameters of the OLED structures can be theoretically simulated by using different quantum chemistry software, like Gaussian or Amsterdam Density Functional, which allow the estimation of the HOMO and LUMO levels for the organometallics, together with their charge transport properties and the influence of the spin-orbit coupling on the photophysical properties of these materials [34][35][36].…”