Indolo[3,2,1-jk]carbazole-Derived Narrowband Violet–Blue Fluorophores: Tuning the Optical and Electroluminescence Properties by Chromophore Juggling

Abstract

The development of rigid polyaromatic building blocks for narrowband violet fluorophores has received tremendous attention. Herein, we designed and synthesized two new triangle-shaped rigid building blocks, namely, 2,5-di-tert-butylindolo­[3,2,1-jk]­carbazole (tBuICz) and 2,11-di-tert-butylindolo­[3,2,1-jk]­carbazole-4-carbonitrile (tBuICzCN), and tethered them with different chromophores to yield a series of violet–blue fluorophores, viz., ICzTPA–ICzPICN, and studied their structure–function relationship. The appended chromophores and cyano unit played a vital role in controlling the optical and electrical properties of the compounds. Except triphenylamine-substituted derivatives, the compounds showed pure violet emission (λem ≤ 403 nm). Intriguingly, the compounds exhibited narrow-band emission with a full-width at half-maximum ≤ 40 nm, attributed to the rigidity of the ICz core. The emission of the compounds displayed positive solvatochromism, which is ascribed to the photoinduced intramolecular charge transfer in the excited state. The compounds revealed excellent thermal robustness with T 5d ≥ 363 °C. The triphenylamine-featuring derivatives displayed a high-lying HOMO compared to their congeners due to their electron-rich nature. When we applied these materials in organic light-emitting diodes, ICzPI outperformed in the series with an EQEmax of 3.07% and a current efficiency of 1.04 cd/A. Notably, its CIEy ∼ 0.046 precisely matched with the Rec.2020 standard of deep-blue color (CIEy ∼ 0.046).

Synthetic progress of organic thermally activated delayed fluorescence emitters via C–H activation and functionalization

“…134,135 The key CÀH bond transformation relies on base-promoted b-hydrogen elimination, supporting the formation of ICz skeletons. Due to the specific arrangement wherein one nitrogen atom is linked with three fused aromatic units, ICz reveals unique FMO distribution and electronic effect, 136,137 making it a distinctive building block for designing TADF materials with new properties. Recently, derivatives of ICz with multiple resonance features and highly efficient narrowband emission have attracted wide attention from material and optoelectronic researchers.…”

Solubility Determination and Modeling of 9,9-Dihexyl-2,7-dibromofluorene in Twelve Solvent Systems at 283.15–323.15 K

“…Polyfluorenes (PFs) are a kind of blue light-emitting materials with excellent properties. , PFs with wide band gaps, excellent thermal and chemical stability, and high quantum efficiency are garnering an increasing amount of research interest. , In particular, studies on 9,9-disubstituted fluorene-based polymers have demonstrated that such PF derivatives can effectively enhance the solubility and processability of PFs. − The 9,9-Dihexyl-2,7-dibromofluorene (F6-Br) with a typical structure of 9,9-disubstituted fluorene-based halohydrocarbon (Figure ) is an important intermediate product in the synthesis of 9,9-disubstituted fluorene-based polymers. − The purity of F6-Br has a significant impact on the characteristics of the generated polymer in this type of synthesis reaction, and side reactions caused by impurities in the reactants often result in low-quality polymers with a low molecular weight and poor regioregularity. − Small levels of fluorenone in the reactants, for example, can increase the likelihood of ketone defects forming in the produced polymers, lowering the color purity, and decreasing the device longevity, while the partial substitutional oxidation of fluorenes produces these fluorenones, which can be efficiently reduced by monomer purification . The solvent/antisolvent (SAS) method has been one of the efficient methods to purify organic molecules for advanced applications. − The solubility of materials in various organic solvents is an important parameter for solution treatment and crystallization. − Therefore, it is critical to investigate the dissolution and purification of F6-Br in various solvents for advanced applications.…”