Electronic correlations in organometallic complexes

Abstract

We investigate an effective model for organometallic complexes (with potential uses in optoelectronic devices) via both exact diagonalisation and the configuration interaction singles (CIS) approximation. This model captures a number of important features of organometallic complexes, notably the sensitivity of the radiative decay rate to small chemical changes. We find that for large parameter ranges the CIS approximation accurately reproduces the low energy excitations and hence the photophysical properties of the exact solution. This suggests that electronic correlations do \emph{not} play an important role in these complexes. This explains why time-dependent density functional theory works surprisingly well in these complexes.Comment: 11 pages, 6 figure

Properties of materials for organic light emitting diodes

“…The line is a best fit for the predicted dependence between the inverse fourth power of the radiative rate and the singlettriplet energy gap. 205 The calculated radiative rate is the same order of magnitude as the experimentally measured rate. 19 Table 3.1 Selected properties of Ir(ptz) 3 and Ir(ppy) 3 at 300 K; from Lo et al 19 Table 4.2 The measured optical energy gaps from low temperature absorption spectroscopy, oxidation potentials from cyclic voltammetry, 19 and the orbital energies from scalar relativistic DFT However, beyond their use in displays, OLEDs are also attracting attention for their application in unique lighting solutions.…”

“…Generically, one expects that such accidental near degeneracies will be most important in regions with high densities of states. 205 This is indeed borne out by the calculations reported above where these issues are slightly more prominent in the MLCT band of Ir(ppy) 3 than they are in the MLCT band of Ir(ptz) 3 .…”

“…In particular, there is an indirect relativistic stabilisation of the MLCT states. This means that indirect relativistic effects increase the degree to which SOC can hybridise singlet and triplet states 205 and hence plays an important role in determining the optical properties of these complexes. The low energy spectra of these two complexes share very similar structures and can be qualitatively understood in the same terms.…”

“…209 It has recently been shown that for a simple (and exactly soluble) model of organometallic complexes, such as those discussed in this paper, the configuration interaction singles (CIS) approximation gives accurate results. 205 The and therefore relatively weakly correlated. As one expects TDDFT to outperform CIS for this problem this suggests that TDDFT will be reliable, consistent with the excellent agreement found between these calculations and experiment.…”

“…This effect is important because the closer the singlet is in energy to a triplet the more strongly spin-orbit coupling can hybridise the two states. 205 Thus the indirect relativistic effect increases the phosphorescent decay rate and hence increases the PLQY of these complexes.…”