Phenothiazine-based bipolar green-emitters containing benzimidazole units: synthesis, photophysical and electroluminescence properties

Abstract

A series of bipolar green emitters bearing hole-transporting phenothiazine and electron-transporting Nphenylbenzimidazole are synthesized and characterized by their photophysical, electrochemical and thermal properties. All the dyes exhibited solvent dependent emission characteristics indicative of more polarized excited state probably arising from the enhanced intramolecular charge transfer (ICT) character in the photo-excited state. Dyes possessing two N-phenylbenzimidazole units and pyridine showed larger degree of ICT in the excited state than the remaining dyes as evidenced from the huge solvatochromic shifts in emission spectra. The dyes exhibited facile oxidation attributable to the removal of electron predominantly from the phenothiazine donor. However, the oxidation is positively shifted due to the electronic perturbations arising from the electron-withdrawing N-phenylbenzimidazole and pyridine units. The compounds exhibited marked thermal stability with the high decomposition temperatures in the range, 412-454 °C. Solution processed organic light-emitting diodes fabricated using the dyes as neat hole-transporting emitting layer or dopant emitter in CBP host showed promising device parameters. A dye possessing three phenothiazine units exhibited bright green electroluminescence with maximum luminance of 1,365 cd/m 2 , CIE coordinates (0.314, 0.593) resembling the prescribed NTSC 1987 standards with a current efficiency of 1.9 cd/A at 100 cd/m 2 .

Phenothiazine and carbazole substituted pyrene based electroluminescent organic semiconductors for OLED devices

“…25 In the methoxyphenyl)-9H-carbazol-3-yl)pyrene (PY-CA) and 1, 3, 6, 8-tetrakis(10-(4-methoxyphenyl)-10H-phenothiazin-3-yl)pyrene (PY-PH). Although the carbazole and phenothiazine combination have been reported as an efficient deep blue and green emitting material in OLEDs earlier 26,27 but so far there is no report in the literature about using them in the form of tetra-functionalized pyrene derivatives for any device application. Our results reveal that introduction of carbazole and phenothiazine unit on tetrabromopyrene core is the effective way to design wide band gap electroluminescent materials.…”

Structure-induced optoelectronic properties of phenothiazine-based materials

“…14) via one-step Heck cross-coupling and used it in two different devices as a hole-transporting emitting layer and as a 10 wt% dopant emitter in 4,4 0 -bis(Ncarbazolyl)-1,1 0 -biphenyl (CBP) host, respectively. 75 While both OLEDs emitted light in the green region, the first one showed EQE of 0.4% and a slight increase up to 0.6% was observed in the second device, which was credited to efficient Förster energy transfer from the CBP matrix to 67. Shanmugasundaram and co-workers presented 68-based OLED that also worked in the green region with a B max of 499 cd m À2 .…”

“…75,76 Generally, they are utilized as the host matrix of the emissive organic layer, playing the role of the energy donor but they could also be applied as the dopant emitter. 75,77 Possessing strong electron-donating features, and many favorable properties as pointed out above, PTZs are considered as strong candidates for LED applications. In this section, we summarize the most recently published results on the use of PTZ-derivatives in OLEDs (see Fig.…”

Simple Synthesis of Red Iridium(III) Complexes with Sulfur-Contained Four-Membered Ancillary Ligands for OLEDs

“…In particular, the Ir(III) complexes with diverse ligands are by far the most effective heavy metal complexes of triplet emitters for phosphorescent OLEDs due to the relative short excited lifetime and high efficiency [6,7]. However, in most cases, the ancillary ligands of Ir(III) complexes mainly rely on six-or five-membered ring structures such as acetylacetonate (acac), picolinate (pic), and tetraphenylimidodiphosphinate [8]. Four-membered ancillary ligands are rarely researched because the conventional idea believes that the materials containing four-membered rings are not stable.…”

“…However, in most cases, the ancillary ligands of Ir(III) complexes mainly rely on six- or five-membered ring structures such as acetylacetonate (acac), picolinate (pic), and tetraphenylimidodiphosphinate [ 8 ]. Four-membered ancillary ligands are rarely researched because the conventional idea believes that the materials containing four-membered rings are not stable.…”