First-Principles Prediction for Phosphorescence Spectra of Tetradentate Platinum(II) Complexes with Narrow Emission Width

Heavy metal complexes are important organic light-emitting diode (OLED) materials, with the advantage of theoretically up to 100% quantum efficiency, but suffer from low color purity, specifically due to a large emission spectral width. Recently, several tetradentate platinum(II) complexes have been found to demonstrate a narrow emission width. In order to suggest a molecular design strategy to achieve narrow emission width, we combine density functional theory (DFT) and its time-dependent formalism coupled with the thermal vibrational correlation function (TVCF) formalism to evaluate the emission energy and spectral line shape for 50 tetradentate platinum(II) complex compounds. We have benchmarked the computational approach by testing 14 xc-functionals and 4 potential energy surface models. We find that the pyridine-carbazole-oxygen structure is the essential moiety to achieve high color purity for the Pt(II) coordination compounds, which can suppress the excitation of low-frequency vibrational relaxation motion during phosphorescence emission, leading to a narrow emission spectrum.