What are the difference between the homo and lumo energy levels and the electronically excited state of molecules in the oleds device
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Presentation of the energy levels, HOMO–LUMO gap and orbital composition distribution of the HOMO and LUMO for ( 1–5 ) complexes. The energy levels, HOMO–LUMO gap for the host material 22 ( TCTA , TPBI )
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The effect of substituted 1,2,4-triazole moiety on the emission, phosphorescent properties of the blue emitting heteroleptic iridium(III) complexes and the OLED performance: a theoretical study
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Jul 2014
Ruby SrivastavaJoshi Laxmikanth Rao
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... respect to eqn (10), z Ir-5d represents the one electron SOC constant of the 5d electron of the Ir ion and C d xy and C d xz represent the coefficients of the 5d orbital related to HOMO and HOMO À 1 respectively. Furthermore, theoretical values of z Ir-5d = 4430 cm À 1 for the Ir( III ) ion 47,48 are also used in the present article. We could thus evaluate the SOC value by deducing the parameters in eqn (10) through the calculations of the TDDFT method. Thus we assessed the phosphorescence mechanism by calculating the k r value using a crude approxi- mation of the model of the aforesaid one-center SOC element, together with eqn (9) and (10). A sketch of the structures of the five molecules is presented in Fig. 1. The main geometrical structural parameters together with the experimental X-ray crystal data are given in Table S1 (ESI † ). It is well known that the observed differences in the optoelectronic and photophysical properties of these complexes depend mainly on the ground state electronic structure. So to gain a better understanding of these molecular structures, the optimized geometrical parameters for the ground states and triplet states of the investigated molecules are tabulated in Table 1. As shown in Fig. 1, all the complexes show a pseudo octahedral co-ordination around the central iridium atom. The difluorophenylpyridine (F 2 ppy) ligands have an Ir–N bond-length of between 2.023–2.042 Å and an Ir–C bond-length of between 2.00–2.02 Å 15,49 which are in very good agreement with the calculated results for the bond lengths of Ir–C which were 1.99–2.01 Å. The Ir–N bond-lengths of 1 and 2 are not effected much by the addition of –Me and –OMe electron-donating substituents to the triazole, but are slightly increased in 3 , 4 and 5 by the addition of the electron withdrawing groups –4FPh, –3,5FPh and –F 5 Ph. This can be rationalized by the fact that the p -accepting ability of the triazole ring is greater than that of the pyridine ring and can be seen by the Mulliken charges of the individual atoms given in Table S2 (ESI † ). The slight difference in the calculated metal–ligand distances can be attributed to the crystal packing in the crystalline state. There is a small difference of 0.2 1 between the experimental and theoretical values for the bond-angles of N3–Ir–N4. For C–Ir–N there is a mean difference of 0.2–0.5 1 between the theoretical values and the experimental values. The Ir–N bonds for 1 and 2 are mainly in the T 1 states for the 1–4 complexes while for complex 5 the bond is contracted compared with those in the S 0 states. If the bond-length of Ir–C1 is slightly larger, then it shows a contracted Ir–C2 in 1–5 . A similar trend is observed for Ir–N3 and Ir–N4 bonds. Because of the stronger interaction between the metal and F 2 ppy in 3–5 , the F 2 ppy ligand has a greater effect on the frontier molecular orbitals (FMOs) in both the ground state and the excited state. Furthermore, this different strength between the metal and the F 2 ppy and the electron donating –Me ( 1 ), –PhOMe ( 2 ) and electron withdrawing –4FPh ( 3 ), –3,5FPh ( 4 ) and –F 5 Ph ( 5 ) results in different electron transition characters. Since the frontier molecular orbital (FMO) is key to gaining a better understanding of the optical and chemical properties of these complexes, we have aimed in this section to implement a detailed examination of the pertinent orbitals. The electron density distributions and FMO energy levels of 1–5 wit
Source publication
The effect of substituted 1,2,4-triazole moiety on the emission, phosphorescent properties of the blue emitting heteroleptic iridium(III) complexes and the OLED performance: a theoretical study
Article
Full-text available
Jul 2014
Ruby SrivastavaJoshi Laxmikanth Rao
View
Context 1
... respect to eqn (10), z Ir-5d represents the one electron SOC constant of the 5d electron of the Ir ion and C d xy and C d xz represent the coefficients of the 5d orbital related to HOMO and HOMO À 1 respectively. Furthermore, theoretical values of z Ir-5d = 4430 cm À 1 for the Ir( III ) ion 47,48 are also used in the present article. We could thus evaluate the SOC value by deducing the parameters in eqn (10) through the calculations of the TDDFT method. Thus we assessed the phosphorescence mechanism by calculating the k r value using a crude approxi- mation of the model of the aforesaid one-center SOC element, together with eqn (9) and (10). A sketch of the structures of the five molecules is presented in Fig. 1. The main geometrical structural parameters together with the experimental X-ray crystal data are given in Table S1 (ESI † ). It is well known that the observed differences in the optoelectronic and photophysical properties of these complexes depend mainly on the ground state electronic structure. So to gain a better understanding of these molecular structures, the optimized geometrical parameters for the ground states and triplet states of the investigated molecules are tabulated in Table 1. As shown in Fig. 1, all the complexes show a pseudo octahedral co-ordination around the central iridium atom. The difluorophenylpyridine (F 2 ppy) ligands have an Ir–N bond-length of between 2.023–2.042 Å and an Ir–C bond-length of between 2.00–2.02 Å 15,49 which are in very good agreement with the calculated results for the bond lengths of Ir–C which were 1.99–2.01 Å. The Ir–N bond-lengths of 1 and 2 are not effected much by the addition of –Me and –OMe electron-donating substituents to the triazole, but are slightly increased in 3 , 4 and 5 by the addition of the electron withdrawing groups –4FPh, –3,5FPh and –F 5 Ph. This can be rationalized by the fact that the p -accepting ability of the triazole ring is greater than that of the pyridine ring and can be seen by the Mulliken charges of the individual atoms given in Table S2 (ESI † ). The slight difference in the calculated metal–ligand distances can be attributed to the crystal packing in the crystalline state. There is a small difference of 0.2 1 between the experimental and theoretical values for the bond-angles of N3–Ir–N4. For C–Ir–N there is a mean difference of 0.2–0.5 1 between the theoretical values and the experimental values. The Ir–N bonds for 1 and 2 are mainly in the T 1 states for the 1–4 complexes while for complex 5 the bond is contracted compared with those in the S 0 states. If the bond-length of Ir–C1 is slightly larger, then it shows a contracted Ir–C2 in 1–5 . A similar trend is observed for Ir–N3 and Ir–N4 bonds. Because of the stronger interaction between the metal and F 2 ppy in 3–5 , the F 2 ppy ligand has a greater effect on the frontier molecular orbitals (FMOs) in both the ground state and the excited state. Furthermore, this different strength between the metal and the F 2 ppy and the electron donating –Me ( 1 ), –PhOMe ( 2 ) and electron withdrawing –4FPh ( 3 ), –3,5FPh ( 4 ) and –F 5 Ph ( 5 ) results in different electron transition characters. Since the frontier molecular orbital (FMO) is key to gaining a better understanding of the optical and chemical properties of these complexes, we have aimed in this section to implement a detailed examination of the pertinent orbitals. The electron density distributions and FMO energy levels of 1–5 wit
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