N-phenylbenzimidazole and trimethylsilyl-containing Pt(II) complexes with short triplet radiative decay of 1.2 μsec for efficient blue-emitting phosphor-sensitized fluorescent organic light-emitting diodes

Abstract

Two novel tetradentate Pt(II) complexes, PtON7-BzPhTMS and PtON7-MeBzPhTMS, were developed by introducing N-phenylbenzimidazole and N-phenyldimethylbenzimidazole moieties to the PtON7 core in place of methylimidazole, aiming to address the challenge of shortening the triplet radiative lifetime (TRL) of blue-emitting Pt(II) complexes for application in phosphor-sensitized fluorescent organic light-emitting diodes (PSF-OLEDs). These structural modifications resulted in markedly shortened TRLs of 1.18 μs for PtON7-BzPhTMS and 1.26 μs for PtON7-MeBzPhTMS, accompanied by photoluminescence emission peaks at 458 and 457 nm with full width at half maximum (FWHM) values of 27 and 26 nm, respectively. Corresponding blue-emitting phosphorescent OLEDs exhibited maximum external quantum efficiencies (EQEs) of 14.6 % and 16.4 %, along with low efficiency roll-off at high luminance. To overcome the low photoluminescent quantum yields of the complexes (<56 %), they were further employed as sensitizers in PSF-OLEDs incorporating the terminal emitter, mBP-DABNA-ME. These PSF-OLEDs achieved maximum EQEs of up to 24.0 % with an FWHM of 26 nm. Notably, the short TRLs of the complexes enabled a 1.5-fold improvement in efficiency roll-off characteristics of the PSF-OLEDs compared to the OLED without the sensitizer (Pt-complex). These findings highlight the importance of shortening the TRL of Pt-complexes to realize efficient blue-emitting OLEDs with reduced efficiency roll-off.