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

Abstract

Cyclometalled Ir(III) compounds are the preferred choice as organic emitters in Organic Light Emitting Diodes. In practice, the presence of the transition metals surrounded by carefully designed ligands allows the fine tuning of the emission frequency as well as a good efficiency of the device. To support the development of new compounds the experimental measurements are generally compared with ab-initio calculation of the absorption and emission spectra. The standard approach for these calculations is TDDFT with hybrid exchange and correlation functional like the B3LYP. Due to 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) 1 arXiv:2001.01959v1 [cond-mat.mtrl-sci] 7 Jan 2020 implemented in gaussian basis sets, to calculate the quasiparticle properties and the adsorption spectra of six cyclometalled Ir(III) complexes going behind TDDFT. In the presented results we compared standard TDDFT simulation with BSE calculations performed on top on perturbative G 0 W 0 and accounting for eigenvalue self consistency.Moreover, in order to investigate in detail the effect of the DFT starting point, we concentrate on Ir(ppy) 3 performing GW-BSE simulations starting from different DFT exchange and correlation potentials.

Low-Order Scaling G0W0 by Pair Atomic Density Fitting

“… 59 , 60 Large numbers of computational material science codes 48 , 56 , 61 − 72 feature GW implementations, and also in the quantum chemistry community, it has acquired some momentum over the last years. 58 , 73 − 93 …”

“…The many body perturbation theory (MBPT) − based on Hedin’s equations describes the correlation of the excited electron with its surrounding by an expansion in powers of the response of the system’s total classical potential to an external perturbation. − In the GW approximation, , this expansion is truncated after first order, which accounts for the major part of electron correlation. ,,, The GW approximation makes MBPT computationally tractable, greatly improves over DFT for the description of single-particle excitations, ,, and also paves the way toward accurate optical spectra using the Bethe-Salpeter equation formalism. , Large numbers of computational material science codes ,,− feature GW implementations, and also in the quantum chemistry community, it has acquired some momentum over the last years. ,− …”

Time-Dependent Density Functional Theory Investigation on the Electronic and Optical Properties of Poly-C,Si,Ge-acenes

“…15,60,61 The many-body perturbation theory can be used to compute optical absorption spectra of molecules and clusters. 62,63 However, while this technique has proven to provide results in very good agreement with high-level quantum chemistry techniques, 64 it is computationally intensive and not suited for a systematic comparative investigation like the one presented here. We estimate exciton-binding energies (E bind ) by subtracting the energy of the first optically active transition (E opt ) from that of the fundamental gap (E gap ): E bind = E gap − E opt .…”

“…We used the frequency space implementation in which the poles of the linear response function correspond to vertical excitation energies and pole strengths represent oscillator strengths . TD-DFT is an efficient and powerful scheme for the calculation of the absorption spectra of finite systems, typically yielding results in very good agreement with available experimental data. ,, The many-body perturbation theory can be used to compute optical absorption spectra of molecules and clusters. , However, while this technique has proven to provide results in very good agreement with high-level quantum chemistry techniques, it is computationally intensive and not suited for a systematic comparative investigation like the one presented here. We estimate exciton-binding energies ( E bind ) by subtracting the energy of the first optically active transition ( E opt ) from that of the fundamental gap ( E gap ): E bind = E gap – E opt . ,, E bind is one of the key parameters regulating the optical absorption of materials .…”

High Intrinsic Phosphorescence Efficiency and Density Functional Theory Modeling of Ru(II)-Bipyridine Complexes with π-Aromatic-Rich Cyclometalated Ligands: Attributions of Spin–Orbit Coupling Perturbation and Efficient Configurational Mixing of Singlet Excited States

“…Cyclometalated transition metal–polypyridine complexes have been the focus of interesting studies on photophysics and excited-state relaxation, ,− and these types of complexes have recently been applied in areas of solar energy conversion, − OLEDs, ,− and photodynamic therapy. , In previous work, the 77 K phosphorescence parameters of Ru-bpy chromophores for the cyclometalated ruthenium­(II)-(2,2′-bipyridine) complexes ([Ru­(bpy) 2 (CM)] + ) with a simply constructed cyclometalated (sc-CM) coordination ligand (sc-CM = 2-phenylpyridine (ppy) and benzo­[ h ]­quinoline (bhq)) showed unusually higher ι em(p) values compared to those of typical [Ru­(bpy) 3– n (Am) 2 n ] 2+ complexes. In addition, in the case of the observed variations in ι em(p) of the emitting 3 MLCT states of the Ru-bpy chromophores for [Ru­(bpy) 2 (sc-CM)] + and typical [Ru­(bpy) 3– n (Am) 2 n ] 2+ complexes, a good linear relation with the intensity component values of ∑SOCM-IS was found, as seen in eq .…”