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

The Journal of Organic Chemistry(2022)

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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 T5d ≥ 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).
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Key words
violet–blue fluorophores,narrowband violet–blue,electroluminescence properties,chromophore juggling,]carbazole-derived
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