Theoretical insight into the photodeactivation pathway of the tetradentate Pt(II) complex: The π‐conjugation effect

In this work, density functional theory and time‐dependent density functional theory were used to investigate the effects of π‐conjugation of the ligand on the photophysical properties, radiative/nonradiative processes and phosphorescence quantum efficiency of tetradentate cyclometalated Pt (II) complex with carbazolyl‐pyridine ligands PtNON . By simulating the absorption spectra and emission wavelengths, increasing the π‐conjugation of the ligand could cause the absorption and emission wavelengths to red‐shift. The results of the computation of key parameters in the radiative decay process, such as singlet‐triplet splitting energy, transition dipole moment and spin‐coupled matrix element between the lowest triplet and singlet excited states, showed that the expansion of π‐conjugation on the carbazole ligand of PtNON resulted in reduction of these parameters, thereby reducing the radiation rate constant. The analyses of the PtNON nonradiative pathway also found that the high activation energy of PtNON made it one of the reasons for the high phosphorescence quantum yield. At the same time, enhancing the molecular orbital delocalization of the ligand further enlarged the energy barrier of the nonradiative pathway, and was conducive to the improvement of phosphorescence quantum yield.