Relativistic Study on Emission Mechanism in Tris(2-phenylpyridine)iridium

Abstract

The mechanisms of radiative processes from electronically excited states were investigated for tris(2phenylpyridine)iridium [Ir(ppy) 3 ]. It was found that low-lying excited singlet and triplet states in the facial (fac) isomer are strongly mixed with each other by spin-orbit coupling (SOC) effects and, as a result, the radiative transitions could occur easily from low-lying spin-mixed states to the lowest spin-mixed state (ground state), where the low-lying spin-mixed states mainly have a triplet character. On the basis of the assumption that radiative processes obey Fermi's Golden rule, large transition probabilities are obtained between the sublevels of the adiabatic lowest triplet state (T 1 ) and the ground state (S 0 ), and phosphorescence is expected to be observed in this complex. This result is in good agreement with experimental reports.

Photo- and field-induced charge-separation and phosphorescence quenching in organometallic complex Ir(ppy)3

“…Interestingly, this behavior is different from one reported so far, 6 where the lifetime increased with application of electric fields up to 2 MV cm −1 and decreased afterwards with further increasing field strength. As already reported so far, 23 the emitting state of Ir͑ppy͒ 3 is not purely a triplet state but the PL originates from low lying spin-mixed metal-to-ligand charge transfer ͑CT͒ states; a charge-separated state is produced following photoexcitation. Then field-induced dissociation of the charge separated state i.e., migration of hole and/or electron takes place prior to their relaxation to the emitting state.…”

Properties of materials for organic light emitting diodes

“…Controlling the electronic and emissive properties of OLED materials remains a key research area from both an experimental and theoretical perspective. [11][12][13][14][15][16][17][18][19] Equally important are the morphology, interfacial interactions and thermal stability of organic thin films, which together play a vital role in device performance, longevity and durability. [20][21][22][23][24][25][26][27] In this thesis both the electronic and morphological properties will be explored with a particular emphasis on phosphorescent OLED designs.…”

“…However, these TDDFT calculations do not, typically, include relativistic effects, such as SOC. 11,13 They are therefore incapable of describing the fine structure of iridium(III) complexes that lowtemperature (LT) spectroscopic measurements reveal. 72,84,96,172,174 This is a major problem as these measurements suggest that the fine structure of the excitations plays an important role in determining optoelectronic properties and hence the performance of OLED's based on these materials.…”

“…11,13,15,86,113,[194][195][196]220 Most approaches taken have included SOC perturbatively. In Chapter 3 it was shown that this approximation accurately reproduces the results of calculations in the two-component formalism, which includes SOC to all orders, in these complexes.…”

“…86 Furthermore, it was seen in Chapter 2 that scalar relativistic effects are also sizeable in these iridium(III) complexes, and play a key role in determining the degree of metal-to-ligand charge transfer (MLCT) character and hence their optical properties. 196 Both Matsushita et al 11 and Jansson et al 113 studied Ir(ppy) 3 with SOC included via the semi-empirical effective nuclear charge method, which includes SOC on top of non-relativistic calculations. Matsushita et al 11 studied the mixing of singlet and triplet states and the implications of this for phosphorescence and Jansson et al 113 investigated the nature of the T 1 excitation in some depth.…”