Phenanthroimidazole‐based chromophores for organic light‐emitting diodes: synthesis, photophysical, and theoretical study

Abstract

Organic light‐emitting diodes (OLED) are gaining attention and making a significant contribution to the area of lighting and displays technology. The synthesis of new materials that can act as a host as well as emissive materials is crucial and efforts have been made in this direction in this research. Here, four star‐shaped fluorophores, with a donor–acceptor (D–A) structure and with triphenylamine and phenanthroimidazole groups with different substitutions at the N1 position of the imidazole moiety, were designed and synthesized. Synthesized fluorophores showed sufficient thermal stability (10% Td in the range 230–280°C). Ultraviolet–visible (UV–vis) spectra of the fluorophores showed multiple absorption bands (bands in the UV region, due to π–π* transitions of the conjugated aromatic portion) and all fluorophores showed blue emission in dichloromethane solution. Electrochemical analysis indicated that all fluorophores had excellent oxidation and reduction characteristics. Theoretical calculations were also performed to better understand the structural and electronic properties of the synthesized fluorophores. All fluorophores had higher triplet (T1) energy (ranging from 2.49–2.52 eV) than the widely used green (Ir(ppy)3 –2.4 eV) and red (Ir (piq)2 acac – 2.2 eV) dopant materials. These results indicated that these fluorophores would be useful as host materials for efficient green and red phosphorescent OLEDs.

Controllable Circularly Polarized Electroluminescence Performance Improved by the Dihedral Angle of Chiral-Bridged Binaphthyl-Type Dopant Inducers

“…The long absorption bands ( S -6 – S -9 ) appear at around 330 nm due to intramolecular charge transfer (ICT) transition . The absorption spectra of S -1 – S -9 become broader bands in cast film compared with their DCM solutions (Figure S3), which can be attributed to intermolecular interaction between chirality inducers . However, no absorption in the visible region was observed, indicating that these inducers S -1 – S -9 can act as an excellent energy donor for fabricating efficient green and red OLEDs …”

“…27 The absorption spectra of S-1−S-9 become broader bands in cast film compared with their DCM solutions (Figure S3), which can be attributed to intermolecular interaction between chirality inducers. 32 However, no absorption in the visible region was observed, indicating that these inducers S-1−S-9 can act as an excellent energy donor for fabricating efficient green and red OLEDs. 33 The photoluminescence (PL) emission of chirality inducers S-1−S-9 were located at the range from 361 to 518 nm in DCM solution (Figure S3).…”

Recent progress in imidazole based efficient near ultraviolet/blue hybridized local charge transfer (HLCT) characteristic fluorophores for organic light-emitting diodes

“…The quantum efficiency consists of the internal quantum efficiency (IQE), which is the ratio of the total number of photons produced in the device to the number of injected charge carriers, and the external quantum efficiency (EQE), which is the ratio of the number of photons emitted from the device to the number of injected charge carriers. 13 Over the past three decades, several types of organic electroluminescent (EL) emitters have been developed, including fluorescent fluorophores, [14][15][16][17][18][19][20][21] phosphorescent fluorophores, [22][23][24][25][26][27] and a new generation of fluorophores involving triplet-triplet annihilation (TTA), [28][29][30][31][32] thermally activated delayed fluorescence (TADF), [33][34][35][36][37] and hybridized local and charge transfer (HLCT). [38][39][40][41] The emission mechanisms of these fluorophores can be divided into three categories: radiative transitions of singlet excitons (fluorescent), radiative transitions of triplet excitons (phosphorescent), and radiative transitions of singlet excitons converted from triplet excitons (TTA, TADF, and HLCT).…”

“…Over the past three decades, several types of organic electroluminescent (EL) emitters have been developed, including fluorescent fluorophores, 14–21 phosphorescent fluorophores, 22–27 and a new generation of fluorophores involving triplet–triplet annihilation (TTA), 28–32 thermally activated delayed fluorescence (TADF), 33–37 and hybridized local and charge transfer (HLCT). 38–41 The emission mechanisms of these fluorophores can be divided into three categories: radiative transitions of singlet excitons (fluorescent), radiative transitions of triplet excitons (phosphorescent), and radiative transitions of singlet excitons converted from triplet excitons (TTA, TADF, and HLCT).…”

Diphenylimidazole Based Fluorophores for Explosive Chemosensors and as Efficient Host Materials for Green Phosphorescent Organic Light Emitting Diodes

“…12 Also, PITTPA shows high thermal stability with high triplet energy, which are used for green Ir(ppy) 3 dopant materials. 13,14 The combination of suitable electron rich and electron deficient moieties in a molecular design result in controlled energy levels for their ability to transfer holes and electrons that are introduced simultaneously. 15 Hence, designing simple organic luminophores that show near UV/deep blue emission in the OLED device is a prerequisite for full color displays.…”