Photodeactivation Channels of Transition Metal Complexes …
273
“nuclear” coherences are not included, being especially the latter of relevance in
the photophysics of TMCs. The limitations in the electronic part will depend on
the inherent limitations of the electronic structure method of choice, and thus, they
are system-dependent and they will need some pre-calibration. Using these dynamical approaches, the ES ultrafast decay of several TMCs has already been modeled,
notably for [Ru(bpy) 3 ]
2+ (see Sect. 3.2) [69, 97], but also for Ir(III) complexes [98].
3 Photodeactivation Channels of TMCs: Selected Recent
Computational Works
3.1 ES Decay Rate Theory and ES Kinetic Modeling:
Calculation of the Temperature-Dependent
Photoluminescence Lifetimes and Efficiencies
of Cyclometalated Ir(III) Complexes
This recent work [37] is selected as a representative example of how the application of
a static approach based on state-of-the-art quantum chemical calculations along with
several ES decay rate theories and kinetic modeling enables the calculations of global
photoluminescence lifetimes and efficiencies of cyclometalated Ir(III) complexes.
Additionally, it is the perfect playground to show how extrinsic factors (temperature
in this case) strongly influence the long timescale ES decay dynamics. Ir(III) complexes are used as dopant materials in state-of-the-art organic light-emitting diode
(OLED) devices. Therefore, as lifetimes and radiative efficiencies are often optimized experimentally in a trial-and-error manner, the development of an accurate
theoretical approach to attain predictions of these magnitudes is acknowledged by
the OLEDs industry. In [37], a general approach to compute temperature-dependent
lifetimes and PLQY of Ir(III) complexes was developed, and its validity was proved
for a blue (1), a green (2), and a yellow/orange (3) emitter (see Fig. 3a). Additionally, the origins of the photoluminescence quenching mechanisms with increasing
temperatures, which importantly reduce the efficiency of blue emitters at OLEDs
standard working conditions, were disclosed. As described in Sect. 2.2, the calculation of phosphorescence rates (k r in Fig. 3b) at the first principles level is currently
attainable based on the Einstein spontaneous emission formula and relying on DFT
and TD-DFT computed data (note that the B3LYP xc functional was used in this study
and SOCs were treated as a perturbation). Two main factors lead to large k r values:
substantial
3 MLCT-S 0 SOCs and efficient intensity borrowing from the manifold of
singlets to the triplets (see Sect. 2.2). Note that the predominant
3 MLCT character of
the T 1 emissive state guarantees very efficient radiative processes, which are often
of the order of 10
5 s
−1 for Ir(III) complexes. Boltzmann statistics of the three spin
sublevels is applied to calculate the overall radiative rate at a given temperature
273
“nuclear” coherences are not included, being especially the latter of relevance in
the photophysics of TMCs. The limitations in the electronic part will depend on
the inherent limitations of the electronic structure method of choice, and thus, they
are system-dependent and they will need some pre-calibration. Using these dynamical approaches, the ES ultrafast decay of several TMCs has already been modeled,
notably for [Ru(bpy) 3 ]
2+ (see Sect. 3.2) [69, 97], but also for Ir(III) complexes [98].
3 Photodeactivation Channels of TMCs: Selected Recent
Computational Works
3.1 ES Decay Rate Theory and ES Kinetic Modeling:
Calculation of the Temperature-Dependent
Photoluminescence Lifetimes and Efficiencies
of Cyclometalated Ir(III) Complexes
This recent work [37] is selected as a representative example of how the application of
a static approach based on state-of-the-art quantum chemical calculations along with
several ES decay rate theories and kinetic modeling enables the calculations of global
photoluminescence lifetimes and efficiencies of cyclometalated Ir(III) complexes.
Additionally, it is the perfect playground to show how extrinsic factors (temperature
in this case) strongly influence the long timescale ES decay dynamics. Ir(III) complexes are used as dopant materials in state-of-the-art organic light-emitting diode
(OLED) devices. Therefore, as lifetimes and radiative efficiencies are often optimized experimentally in a trial-and-error manner, the development of an accurate
theoretical approach to attain predictions of these magnitudes is acknowledged by
the OLEDs industry. In [37], a general approach to compute temperature-dependent
lifetimes and PLQY of Ir(III) complexes was developed, and its validity was proved
for a blue (1), a green (2), and a yellow/orange (3) emitter (see Fig. 3a). Additionally, the origins of the photoluminescence quenching mechanisms with increasing
temperatures, which importantly reduce the efficiency of blue emitters at OLEDs
standard working conditions, were disclosed. As described in Sect. 2.2, the calculation of phosphorescence rates (k r in Fig. 3b) at the first principles level is currently
attainable based on the Einstein spontaneous emission formula and relying on DFT
and TD-DFT computed data (note that the B3LYP xc functional was used in this study
and SOCs were treated as a perturbation). Two main factors lead to large k r values:
substantial
3 MLCT-S 0 SOCs and efficient intensity borrowing from the manifold of
singlets to the triplets (see Sect. 2.2). Note that the predominant
3 MLCT character of
the T 1 emissive state guarantees very efficient radiative processes, which are often
of the order of 10
5 s
−1 for Ir(III) complexes. Boltzmann statistics of the three spin
sublevels is applied to calculate the overall radiative rate at a given temperature