Efficient Blue and Yellow Organic Light-Emitting Diodes Enabled by Aggregation-Induced Emission

Abstract

A new class of donor-bridge-acceptor (D-π-A) π-conjugated light-emitting molecules comprising carbazole as donor and maleimide (Cbz-MI, Cbz-MI(d)), phthalimide (Cbz-Pth) as acceptor units with phenyl ring as spacer have been synthesized in good yields. These compounds exhibit high quantum yield with three distinct emission colors yellowish-green (Cbz-MI), bright yellow Cbz-MI(d), and sky blue (Cbz-Pth) in the solid state. Single-crystal X-ray and quantum chemical calculations reveals that twisting of the phenyl rings with high torsional angle on maleimide and phthalimide units reduce the effective inter-chromophore electronic coupling, furnish dramatic changes in their photophysical properties in solution and solid states. Intriguingly, Cbz-MI(d) and Cbz-Pth exhibits a unique aggregation-induced blue-shifted emission (AIBSE) due to restricted intramolecular rotation (RIR) process, while Cbz-MI shows red-shifted emission in the solid state. The solvatochromic study reveal that combined RIR and excited state migration augment AIE (aggregation-induced emission) properties. The electrochemical properties reveal that Cbz-MI exhibits high oxidation propensity while Cbz-Pth shows low reduction values. Subsequently, organic light-emitting diodes (OLEDs) were fabricated with a simple three-layer device containing Cbz-Pth and Cbz-MI(d) as emitting layers. Cbz-MI(d) exhibits high performance yellow OLED with an external quantum efficiency exceeding ∼4.1% and a brightness exceeding ∼73915 cd/m, which is among the best performance reported for bright yellow fluorescence organic light-emitting diodes.

Facile Synthetic Route for Direct Access of Perylenediimide Single Crystals in High Yield through In Situ Crystallization

“…Self‐assembly of π‐conjugated organic molecules into one‐dimensional (1D) materials are of special interest due to their potential applications in optical, electronic and optoelectronic devices . Molecular organization of π‐conjugated organic molecules strongly influence on the material properties and performance of the devices, such as field effect transistor, organic photovoltaics, organic light emitting diodes (OLED) and electrical conductivity . For instance, self‐assembly of polyaromatic molecules via aromatic stacking into infinite columnar structures resulted in the formation of 1D columnar liquid crystals .…”

“…[1][2][3][4][5][6][7][8][9][10] Molecular organization of π-conjugated organic molecules strongly influence on the material properties and performance of the devices, such as field effect transistor, organic photovoltaics, organic light emitting diodes (OLED) and electrical conductivity. [11][12][13][14][15][16][17] For instance, self-assembly of polyaromatic molecules via aromatic stacking into infinite columnar structures resulted in the formation of 1D columnar liquid crystals. [18][19][20] that showed enhanced electron-transporting and charge carrier mobility along the direction of aromatic stacking.…”

Biphenyl Diimide Based Novel Blue Emitters with Aggregation‐Induced Blue‐Shifted Emission Characteristics

“…This was attributed to the conjugated aromatic imides or diimides suffered red-shifted and quenched fluorescence in film or solid state. [14] Clearly, unsatisfying emission properties of conjugated imides was caused by their rigid plane structures. It can be envisioned that introducing the twisted structure, such as two seven-membered imide rings, should significantly enhance their emission properties and expand their application in OLED.…”

Electronic, optical, and charge transfer properties of porphyrin and metallated porphyrins in different media

“…EL materials are found between ETL and HTL materials and emit light from red to blue depending on the wavelength of the emission. [49][50][51][52] Recently, the scientists have focused on improving the materials having a high charge transfer rate and exhibiting strong emission in the visible region to increase the performance of OLEDs. While TPD is metal-free molecules, Alq3 is metallated organic molecules.…”

“…[40][41][42][43][44][45][46][47][48] Additionally, color properties of emitter materials in EL layer have been studied. [49][50][51][52] Recently, the scientists have focused on improving the materials having a high charge transfer rate and exhibiting strong emission in the visible region to increase the performance of OLEDs. [53][54][55][56][57][58][59] For this purpose, they have modified the compounds via using the metal or substituent.…”