Design, Synthesis, and Optoelectronic Properties of Dendrimeric Pt(II) Complexes and Their Ability to Inhibit Intermolecular Interaction

Dendrimeric Pt­(II) complexes [(C∧N)­Pt­(dpm)] and [Pt­(C∧N)2] (Hdpm = dipivaloylmethane, HC∧N = 1,2-diphenylbenzoimidazole and its derivatives containing the carbazole dendrons) have been synthesized and characterized systematically. All of the complexes display green emission in the range of 495–535 nm that originated from the 360–440 nm absorption bands, which are assigned to dπ­(Pt)→π*­(L) metal-to-ligand charge transfer (MLCT) mixed with intraligand π­(L)→π*­(L) transition. Solution photoluminescence quantum yield (φp 0.26–0.31) of the heteroleptic complexes [(C∧N)­Pt­(dpm)] obviously increases when compared with that of complex [(C∧N)­Pt­(acac)]. Organic light-emitting diode devices based on these Pt­(II) complexes with a multilayer configuration were fabricated and gave desirable electroluminescent (EL) performances, such as non- or less red-shifted EL spectra, in comparison with the photoluminescence spectra and slow efficiency roll-off with increasing brightness or current density. Complex [(t-BuCzCzPBI)­Pt­(dpm)] (where t-BuCzCzPBI = 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))­carbazol-9-yl)­phenyl-2-phenylbenzoimidazole) showed the best performance, with a maximum current efficiency of 29.31 cd/A and a maximum external quantum efficiency (EQE) of 9.04% among the fabricated devices. Likewise, for homoleptic [Pt­(t-BuCzCzPBI)2] dendrimer, the powder φp (0.14) and maximum EQE (0.74%) improve by 7 and 7.4 times, respectively, as high as they do for nondendrimeric [Pt­(1,2-diphenylbenzoimidazole)2] (0.02, 0.10%), although its efficiency is still lower than that of the heteroleptic counterpart due to the severely distorted square-planar geometry of the emitting core. These results reveal that large steric hindrance from ancillary ligand (dpm) or the homoleptic conformation can effectively inhibit intermolecular interaction for these dendrimeric Pt­(II) complexes.