Theoretical Study Of The Impact Of Non-conjugated Nuture In Carbene Ir(Ⅲ) Complexes On The Excited State And Spectrocscopic Properties

In this study we design and investigate electronic structures and spectroscopic properties of several cyclometalated iridium carbene complexes possessing at least one functionalized methylene moiety, (dfpmb)(dfbmb)Ir(mptz) (2),(dfbmb)2Ir(mptz)(3),and(dfbmb)₂Ir(mpmtz)(4)(dfpmbH=1-difluorophenyl-3-methyl-benzimidazoline-2-ylidene;dfbmbH=1-(2,4-difluorobenzyl)-3-(methylbenzimidazolium;mptzH=4-methyl-2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine);mpmtzH=4-methyl-2-(3-methylene-5-(trifluoromethyl)-2H-1,2,4-triazole-3-yl)pyridine)on the basis of their parent (dfpmb)₂Ir(mptz) (1). DFT was conducted to optimize the geometries of the ground state and triplet excited state for 1-4, respectively. The absorption and emissions of 1-4 in CH₂Cl₂ media were calculated using TDDFT associated with PCM model.On the basis of FMOs analysis, it clearly represents that for all examined compounds 1-4, in the ground states, HOMO is almost composed of center metal atom and benzyl (phenyl) part on the dfbmb (dfpmb) ligands, whereas LUMO is located at the ancillary moiety. In addition, the introduction of a saturated methylene group into cyclometalated ligands effectively destabilized both of HOMO and LUMO, directly resulting in the increase in HOMO and LUMO levels, respectively. In our study, the incorporation of the methylene moiety into ligands renders a major influence on LUMO level. Thus, the resulting complexes 1-4 show that energy gaps of HOMO-LUMO follows the order 2 < 1 < 3 < 4. In addition, 2 containing comparable LUMO energy level but higher HOMO is anticipated to bring about a good device performance as compared to all examined complexes. Although the lowest-lying absorptions 370 nm for 1, 372 nm for 2, 364 nm for 3, and 338 nm for 4, can be assigned to MLCT mixing with a certain extent of LLCT, the apparent discrepancy in the oscillators might result from the observation that the LUMO property of 4 is essentially similar to LUMO+1 of the rest of complexes. The pristine mptz LUMO orbital is dissipated under the saturated methylene breaking the largeÏ€-conjugation stream at mpmtz segment. Likewise, the LUMO+1Ï€composition for 4 is extremely similar to the LUMO+2 for 1-3. Meantime, the synergism of the imperfection of the PCM model and the simplification of our chemical computations might lead to the molar extinction coefficient discrepancy observed by between experiment and calculations.A careful examination of results shows: (1) the patterns of the occupied orbitals for 1-4 are almost the same with the HOMO being a admixture of Ir atom and benzyl part, whereas the LUMO is predominately delocalized over the ancillary chelate mptz or mpmtz; (2) the lowest-lying absorption appearing in 370 nm for 1, 372 nm for 2, 364 nm for 3, and 338 nm for 4, can be assigned to the spin-allowed MLCT mixed with a certain amount of LLCT transition; (3) complexes 1-3, especially 4, all exhibit blue emission with maxima wavelengths at 506, 495, 486 and 478 nm, respectively; (4) complex 4 with the relative highest component of 3MLCT can be reasonably expected to have a higher radiative transition rate constant (kr) among 1-4. From the highest absorption peaks, eventually, the molar extinction coefficient discrepancy between experiment and calculations might be tentatively attributable to the synergism of the intrinsic imperfection of the PCM model and the simplification of chemical computations.