Ab Initio Many-Body Perturbation Theory Calculations of the Electronic and Optical Properties of Cyclometalated Ir(III) Complexes

Cyclometalated
Ir­(III) compounds are the preferred choice as organic
emitters in organic light-emitting diodes. In practice, the presence
of the transition metal surrounded by carefully designed ligands allows
fine-tuning of the emission frequency as well as good efficiency of
the device. To support the development of new compounds, experimental
measurements are generally compared with absorption and emission spectra
obtained from ab initio calculations. The standard approach for these
calculations is time-dependent density functional theory (TDDFT) with
a hybrid exchange–correlation functional like B3LYP. Because
of the size of these compounds, the application of more complex quantum
chemistry approaches can be challenging. In this work, we used many-body
perturbation theory approaches, in particular the GW approximation
with the Bethe–Salpeter equation (BSE) implemented in Gaussian
basis sets, to calculate the quasiparticle properties and the absorption
spectra of six cyclometalated Ir­(III) complexes, going beyond TDDFT.
In the presented results, we compared standard TDDFT simulations with
BSE calculations performed on top of perturbative G0W0 and accounting for eigenvalue self-consistency. Moreover,
in order to investigate in detail the effect of the DFT starting point,
we concentrated on Ir­(ppy)3 and performed GW-BSE simulations
starting from different DFT exchange–correlation potentials.