Nondoped Deep‐Blue Organic Light‐Emitting Diodes with Color Stability and Very Low Efficiency Roll‐Off: Solution‐Processable Small‐Molecule Fluorophores by Phosphine Oxide Linkage

Abstract

A series of solution-processable small molecules PO1-PO4 were designed and synthesized by linking N-phenylnaphthalen-1-amine groups to a phenyl phosphine oxide core through a π-conjugated bridge, and their thermal, photophysical, and electrochemical properties were investigated. The phosphine oxide linkage can disrupt the conjugation and allows the molecular system to be extended to enable solution processability and high glass transition temperatures (159-181 °C) while preserving the deep-blue emission. The noncoplanar molecular structures resulting from the trigonal-pyramidal configuration of the phosphine oxide can suppress intermolecular interactions, and thus these compounds exhibit strong deep-blue emission both in solution and the solid state with high photoluminescent quantum yield (PLQY) of 0.88-0.99 in dilute toluene solution. Solution-processed nondoped organic light-emitting diodes featuring PO4 as emitter achieve a maximum current efficiency of 2.36 cd A(-1) with CIE coordinates of (0.15, 0.11) that are very close to the NTSC blue standard. Noticeably, all devices based on these small-molecular fluorescent emitters show striking deep-blue electroluminescent color stability and extremely low efficiency roll-off.

Pure-organic phosphine oxide luminescent materials

“…In 2012, Yang and Ma et al used P = O as a linker and an electron-transporting unit to construct a series of PO blue emitters, PO1-PO4, with phenylene and 2,7-fluorenyl bridges and N-phenylnaphthalen-1-amine as hole-transporting moieties (Table 1 and Figure 4) [32]. The non-coplanar molecular structure produced by the triangular pyramidal configuration of P = O can inhibit intermolecular interactions, making these compounds show deep-blue emissions with high φ PL values of 88-99% both in solution and the solid state.…”

Organophosphorus derivatives for electronic devices

“…4). 40 These structures allowed authors to obtain balanced charge transport and deep blue emission. EQE up to 2.06% was achieved with P2 and very low efficiency roll-off.…”

Carbazole-functionalized polyphenylene-decorated solid state emissive D–A–D molecules: reduced donor–acceptor interaction and enhanced emission in the solid state

“…These systems are anticipated to simplify the device configuration by reducing the number of active layers and consequently improving the device performance. [4][5][6][7][8][9][10][11][12][13] However, most of the conjugated D-A molecules show very high luminescence efficiency in dilute solutions only, and exhibit large bathochromic shift with relatively weak or no emissions in thin film due to aggregation caused quenching (ACQ) effect. This ACQ may be attributed to the facilitated non radiative decay induced by strong intermolecular interactions, including exciton coupling and excimer formation.…”