Synthesis and density functional theory study of iridium (III) complexes with pyridinylformidamide ancillary ligand for efficient blue ohosphorescent

This study aims to synthesise and characterise new blue phosphorescent iridium(III) complexes and investigate their structural and photophysical properties through experimental techniques and theoretical calculations. Complexes of bis(phenylpyridine)(2,6- difluorobenzylpyridinylformimidamide) iridium(III) (IR1), bis(2,4- difluorophenylpyridine)(2,6- difluorobenzylpyridinylformimidamide)iridium(III) (IR2), bis(phenylpyridine)(4- methylbenzylpyridinylformimidamide)iridium(III) (IR3) and bis(2,4- difluorophenylpyridine)(4- methylbenzylpyridinylformimidamide)iridium(III) (IR4) were synthesised by reaction between dichloro-bridged iridium(III) dimers with the respective triazolium salts. Characterisation was conducted using carbon, hydrogen and nitrogen (CHN) elemental analyser and spectroscopic techniques: nuclear magnetic resonance (NMR), Fourier transform-infrared (FT-IR) and liquid chromatography-mass spectrometry (LC-MS). Photophysical properties were examined using ultravioletvisible (UV-Vis), fluorescence and photoluminescence (PL) spectroscopy. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations with the B3LYP functional and LanL2DZ basis set were used to evaluate ground state geometries and electronic transitions. IR spectra showed strong _(C_N) stretching bands between 2220_2224 cm-1 for all complexes. In 1H NMR spectra, the disappearance of singlet protons from triazolium salts confirmed complex formation, while 13C NMR displayed nitrile carbon peaks between 116.7_118.6 ppm. X-ray crystallographic study verified the iridium was coordinated to two phenylpyridine ligands and one pyridinylformimidamide ancillary ligand in a distorted octahedral geometry. Emission spectra showed that IR2 (_em=463 nm) and IR4 (_em=464 nm) resulted slightly blue emission in dichloromethane solution compared to the green emission of IR1 and IR3 (_em= 518 nm). IR3 displayed the highest phosphorescence quantum yield (49%) and the longest lifetime (_ = 78.82 ns). DFT calculations showed that IR4 has the largest band gap (3.88 eV), consistent with the experimental NMR chemical shifts and IR vibrational modes. In conclusion, new blue phosphorescent iridium(III) complexes were successfully synthesised and characterised using both experimental techniques and theoretical calculations. IR4 exhibited a notable, blueshifted emission and the largest band gap. As implication, IR4 has a high potential for application in blue organic light-emitting diode (OLED) devices.