PtII(C∧N)(N-donor Ligand)cl-Type Complexes with the Four-Coordinate Organoboron Unit and Their Optoelectronic Properties

In this research, we have developed a series of Pt-II(C<^>N)(N-donor ligand)Cl-type phosphorescent complexes with the four-coordinate organoboron unit in the C<^>N ligand. Through shifting the coordinating position of the Pt(II) center from phenyl ring to pyridyl ring of the 2-phenylpyridine-type (ppy-type) four-coordinate organoboron unit, the variation of >50 nm in charge-transfer (CT) absorption band and >40 nm in phosphorescent wavelength can be observed in the synthesized Pt-II(C<^>N)(N-donor ligand)Cl-type complexes, indicating effective tuning of their photophysical properties incurred by the four-coordinate organoboron unit. In addition, based on the cyclic voltammetry result, obvious variation of electron density on the Pt(II) center of these Pt-II(C<^>N)(N-donor ligand)Cl-type phosphorescent complexes can also be observed. Critically, these Pt-II(C<^>N)(N-donor ligand)Cl-type complexes with the ppy-type four-coordinate organoboron unit can exhibit aggregation enhanced phosphorescent emission (AEPE) behavior. It seems that the hydrogen bonding among the N-donor ligands and water molecules can affect their AEPE response greatly, representing a new way to tune the AEPE behavior in the Pt-II(C<^>N)(N-donor ligand)Cl-type complexes. In the solution-processed organic light-emitting diodes (OLEDs), peak electroluminescent (EL) efficiencies of 15.3%, 10.3 cd A(-1) and 9.8 lm W-1 have been achieved with EL at ca. 648 nm. These impressive results have provided key information for tuning optoelectronic properties of the Pt-II(C<^>N)(N-donor ligand)Cl-type complexes by the four-coordinate organoboron unit and N-donor ligand.