TD-DFT investigation of electronic structures, photophysical properties and the theoretical design of OLEDs based on phosphorescent Ir(III) complexes bearing the non-πelectron-conjugated carbene ligand

摘要

In the search for efficient phosphorescent materials, a rational design is presented for the iridium complex material (dfbmb)Ir(fptz)_2 (2) (dfbmb=1-(2,4-difluorobenzyl)-3-methylbenzimidazolium), which involves the use of two 2-pyridyl triazolate (fptz) chromophores and a non- electron-conjugated high-field ligand dfbmb assembled by a saturated -bond methylene group, and a comparison with the benchmark (dfbmb) _2Ir(fptz) (1). In this work the electronic structures, absorption and phosphorescence spectra were investigated using the TD-DFT method. In order to obtain the mechanism of high phosphorescence yield in (1) and estimate the radiative rate constant k_r for (2), the radiative rate constant k~r, the spin-orbital coupling (SOC) matrix element, E(ST), and the square of the SOC matrix element (ψS _1HSOψT ~12) for (1) and (2) were measured. It is concluded that the switch of the cyclometalated ligand from the main chelate to the ancillary chelate seems to enhance the splitting of E(ST) in the current system. Finally, using the information gained, a PhOLED utilizing (1) and (2) was designed.