ABSTRACT
Herein, we report the synthesis and characterization of two Pt(II) coordination compounds, the new platinum(II)[N,N'-bis(salicylidene)-3,4-diaminobenzophenone)] ([Pt(sal-3,4-ben)]) and the already well-known platinum(II)[N,N'-bis(salicylidene)-o-phenylenediamine] ([Pt(salophen)]), along with their application as guests in a poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) conjugated polymer in all-solution processed single-layer white organic light-emitting diodes. Completely different performances were achieved: 2.2% and 15.3% of external quantum efficiencies; 2.8 cd A-1 and 12.1 cd A-1 of current efficiencies; and 3103 cd m-2 and 6224 cd m-2 of luminance for the [Pt(salophen)] and [Pt(sal-3,4-ben)] complexes, respectively. The Commission Internationale de l'Eclairage (CIE 1931) chromaticity color coordinates are (0.33, 0.33) for both 0.1% mol/mol Pt(II):PFO composites at between approximately 3.2 and 8 V. The optoelectronic properties of doped and neat PFO films have been investigated, using steady-state and time-resolved photoluminescence. Theoretical calculations at the level of relativistic density functional theory explained these results, based on the presence of the Pt(II) central ion's phosphorescence emission, considering spin-orbit coupling relationships. The overall results are explained, taking into account the active layer morphological properties, along with the device's electric balance and the emitter's efficiencies, according to deep-trap space-charge models. Considering the very simple structure of the device and the ease of synthesis of such compounds, the developed framework can offer a good trade-off for solution-deposited white organic light-emitting diodes (WOLEDs), with further applications in the field of lighting and signage.
ABSTRACT
A salicylidene derivative, N,N'-bis(salicylidene)-(2-(3',4'-diaminophenyl)benzothiazole) (BTS), reactive in the Excited State Intramolecular Proton Transfer (ESIPT) process, was synthesized and its photophysical properties were evaluated, presenting an emission covering the entire range of the visible spectrum. Due to its broad emission band, BTS was successfully tested as an active layer in solution-processed organic light-emitting diodes with white-light emission. These diodes were prepared using solution-based protocols with the dye solubilized in a poly(9-vinylcarbazole) matrix. Different guest : host (polymer : BTS) molar ratios were used to optimize the diode performance. The optimized architecture rendered the best so far all-solution-processed ESIPT OLED with a luminance of 34 cd m-2 at 13.5 V with CIE coordinates 0.31, 0.40.