Efficient Deep‐Blue Electroluminescence Based on Phenanthroimidazole‐Dibenzothiophene Derivatives with Different Oxidation States of the Sulfur Atom

Abstract

Developing efficient deep-blue materials is a long-term research focus in the field of organic light-emitting diodes (OLEDs). In this paper, we report two deep-blue molecules, PITO and PISF, which share similar chemical structures but exhibit different photophysical and device properties. These two molecules consist of phenanthroimidazole and dibenzothiophene analogs. The distinction of their chemical structures lies in the different oxidation states of the S atom. For PITO, the S atom is oxidized and the resulting structure dibenzothiophene S,S-dioxide becomes electron deficient. Therefore, PITO displays remarkable solvatochromism, implying a charge-transfer (CT) excited state formed between the donor (D) phenanthroimidazole and acceptor (A) dibenzothiophene S,S-dioxide. For PISF, it is constituted of phenanthroimidazole and dibenzothiophene in which the S atom is not oxidized. PISF displays locally excited (LE) emission with little solvatochromism. Compared with PISF, the D-A molecule PITO with an electron-deficient group shows a much lower LUMO energy level, which is in favor of electron injection in device. In addition, PITO exhibits more balanced carrier transport. However, PISF is capable of emitting in the shorter wavelength region, which is beneficial to obtain better color purity. The doped electroluminescence (EL) device of the D-A molecule PITO manifests deep-blue emission with CIE coordinates of (0.15, 0.08) and maximum external quantum efficiency (EQE) of 4.67 %. The doped EL device of the LE molecule PISF, however, reveals an even bluer emission with CIE coordinates of (0.15, 0.06) and a maximum EQE of 4.08 %.

Highly efficient and stable pure blue nondoped organic light-emitting diodes at high luminance based on phenanthroimidazole-pyrene derivative enabled by triplei-triplet annihilation

“…With the investigations of TTA processes in blue OLEDs deepening, researchers were mainly focused on fused polycyclic aromatic cores such as anthracene (An) [26−29] and pyrene (Py) [19,22,29−31], whose double energy of triplet is larger than singlet one, i.e., 2ET1>ES1, making them capable of up-converting triplets into singlets through TTA [32]. We have confirmed in our previous studies that phenanthroimidazole (PI) group is an excellent skeleton to construct saturate blue emitter for its high photoluminescence quantum efficiency (PLQY) and balanced ambipolar carrier transport properties capable of depress the efficiency roll-off [33][34][35][36][37].PI based derivatives exhibited some intriguing properties that the aryl substituents linked at position of imidazole C2 can extend the π-conjugation, judiciously adjust the electronic properties, provide effective hindrance to interchromophore packing and improve PLQY.…”

Efficient Red Electroluminescence From Phenanthro[9,10‐d]imidazole‐Naphtho[2,3‐c][1,2,5]thiadiazole Donor‐Acceptor Derivatives

“…[39][40][41][42][43] In addition, the highest occupied molecular orbital (HOMO) energy level of PI is similar to that of carbazole and can match well with the HOMO of some carbazole based hole transporting materials such as 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA), which is in favor of hole injection from hole transporting layers to the emitting layer. [44][45][46] Previously, we have applied PI as the donor to construct a series of blue-emitting DÀ A materials and some of them showed fairly good device performance. [44][45][46] However, PI is barely used as donor to construct red-emitting DÀ A molecules probably due to its relatively weak electron donating ability and its wide optical gap.…”

“…[44][45][46] Previously, we have applied PI as the donor to construct a series of blue-emitting DÀ A materials and some of them showed fairly good device performance. [44][45][46] However, PI is barely used as donor to construct red-emitting DÀ A molecules probably due to its relatively weak electron donating ability and its wide optical gap. We believe that PI can be a good building block for red-emitting DÀ A molecules.…”

Exploration of High Efficiency AIE‐Active Deep/Near‐Infrared Red Emitters in OLEDs with High‐Radiance

“…After then, the commercial TPA‐based boronic acid was introduced to connect with DBr‐NZ, and the monosubstituted intermediate of TNZ‐Br was obtained via classical palladium‐catalyzed Suzuki reaction. Alternately, three PPI‐Br derivatives were prepared via tuning structures of corresponding aromatic amines (aniline, 4‐tert‐butylaniline, and 3,5‐di‐tert‐butylaniline) as our previous reports, and their borate esterification (PPI‐B) process were done with yields of 58–74% according to the literatures with slight modification . Employing the Suzuki reaction again, three TNZPs were obtained, and purified by column chromatography, whose structures were confirmed by spectroscopical characterization using nuclear magnetic resonance spectroscopy (Figures S21–S26, Supporting Information) and high‐resolution mass spectrometry (Figures S2–S4, Supporting Information).…”