A Novel Deep Blue-Emitting Zn^II Complex Based on Carbazole-Modified 2-(2-Hydroxyphenyl)benzimidazole: Synthesis, Bright Electroluminescence, and Substitution Effect on Photoluminescent, Thermal, and Electrochemical Properties

Abstract

A novel deep blue-emitting Zn II complex Zn(L c ) 2 (L c -) 2-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo [d]imidazol-2-yl)phenolate) based on a carbazole-functionalized N^O ligand was synthesized by a modified method. Other two Zn II complexes (Znwere also prepared for comparison. The remarkable substitution effect on the photoluminescent and thermal properties of the complexes was studied. The investigation indicated an unexpected amplifying hypsochromic effect of the substituents on the emission of the complex in the solid state: the larger substituent corresponded to the larger blue shift of the emission of the complex (Zn(L c ) 2 has the shortest emission wavelength of 422 nm as the deep blue emission among these three complexes). The stronger steric effect induced by the bulky substitutions should be one of the most important factors. Among the three Zn II complexes, the temperature of decomposition of Zn(L c ) 2 is the highest at 427 °C. Cyclic voltammetry (CV) of the complexes showed that the carbazole moieties remarkably improved the hole injection ability of Zn(L c ) 2 with the HOMO energy level 0.6 eV higher than those of Zn(L a ) 2 and Zn(L b ) 2 . The good hole injection and transporting ability of Zn(L c ) 2 was further proved by its three-layer devices, in which the electroluminescent (EL) emission mainly originated from the electron-transporting Alq 3 layer. Through the four-layer devices with the hole-blocking layer, the pure blue emission of Zn(L c ) 2 at 452 nm was demonstrated. Zn(L c ) 2 seems favorable among the blue-emitting Zn II complexes with a brightness more than 2000 cd m -2 , a high efficiency stability, and an excellent EL spectra stability.

Modulation of Excited‐State Proton Transfer of 2‐(2′‐Hydroxyphenyl)benzimidazole in a Macrocyclic Cucurbit[7]uril Host Cavity: Dual Emission Behavior and pKa Shift

“…[2][3][4] Molecules showing ESIPT behavior have potential applications as fluorescence probes, UV filters, UV photostabilizers, molecular switches, and light emitting diodes. [5][6][7][8] 2-(2'-Hydroxyphenyl)benzimidazole (HPBI) is one such molecule that exhibits ESIPT on the sub-picosecond timescale, and has been studied quite extensively in different solvents and in restricted media. [1,[9][10][11] In the ground state, the most stable form of this molecule is its normal enol form (E), which features an acidic hydroxyl group and a basic nitrogen atom, and this form can also adopt either cis or trans configurations.…”

Synthesis, structural and optical properties of 1-alkyl-2-(2’-tosylaminophenyl)-5-nitrobenzimidazoles and their zinc(II) complexes

“…Among the benzimidazole containing coordination compounds lately more attention was given to the zinc complexes of 2-(2'-hydroxyphenyl)benzimidazoles with N 2 O 2 ligand environment due to their photoluminescence (PL) and electroluminescence properties(EL) and the possibility to use above complexes as emissive and electron-transport layers in the Organic light emitting diodes OLED [10][11][12][13], e.g. Zn(BIZ) 2 (BIZ = 1-Phenyl-2-(2'-hydroxyphenyl)benzimidazole) showed pure blue emission with a peak wavelength of around 450 nm and calculated Commission Internationale de l'Éclairage CIE color coordinates of around (0.17, 0.16) [12].…”

Optoelectronic characterization of zinc complexes for display device applications

“…The design and fabrication of efficient light emitting devices are greatly developing due to their potential application in numerous display technology [1][2][3][4][5]. Most significant applications are in the area of full color flat panel displays and future energy saving alliances.…”

“…Zinc complexes have also shown excellent light emitting and charge transporting properties. The energy gap between HOMO-LUMO responsible for electronic transition states, efficiency and emission wavelength of devices, can be tuned by modifying structure of ligands or changing metal ions [2][3][4][5]. The absorption and emission wavelengths are influenced by electronic nature of the ligands and their substituent's.…”