Introduction

Evolution of organic light-emitting diodes (OLEDs) reached the point, which allows to obtain maximum internal quantum efficiency of 100% partly using heavy-metal-free emitters exhibiting thermally activated delayed fluorescence (TADF). Such emitters are also predictively perfect candidates for new generation of optical sensors since triplet harvesting can be sensitive to different analytes (at least to oxygen). Although many organic TADF emitters have been reported so far as OLED emitters, the investigation of materials suitable for both OLEDs and optical sensors remains extremely rare.

Objectives

Aiming to achieve high photoluminescence quantum yields in solid-state and triplet harvesting abilities of organic semiconductors with efficient bipolar charge transport required for application in both blue OLEDs and optical sensors, symmetrical donor–acceptor-donor organic emitters containing pyrimidine-5-carbonitrile electron-withdrawing scaffold and carbazole, tert-butylcarbazole and methoxy carbazole donor moieties were designed, synthesized and investigated as the main objectives of this study.

Methods

New compounds were tested by many experimental methods including optical and photoelectron spectroscopy, time of flight technique, electrochemistry and thermal analyses.

Results

Demonstrating advantages of the molecular design, the synthesized emitters exhibited sky-blue efficient TADF with reverse intersystem crossing rates exceeding 10⁶ s⁻¹, aggregation-induced emission enhancement with photoluminescence quantum yields in solid state exceeding 50%, hole and electron transporting properties with charge mobilities exceeding 10^-4 cm²/V·s, glass-forming properties with glass transition temperatures reaching 177 °C. Sky-blue OLEDs with non-doped light-emitting layers of the synthesized emitter showed maximum external efficiency of 12.8% while the doped device with the same emitter exhibited maximum external efficiency of 14%. The synthesized emitters were also used as oxygen probes for optical sensors with oxygen sensitivity estimated by the Stern-Volmer constant of 3.24·10^-5 ppm⁻¹.

Conclusion

The developed bipolar TADF emitters with pyrimidine-5-carbonitrile and carbazole moieties showed effective applicability in both blue OLEDs and optical sensors.

中文翻译：

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嘧啶-5-腈的多功能衍生物和不同取代的咔唑用于无掺杂天蓝色 OLED 和氧的发光传感器

介绍

有机发光二极管 (OLED) 的发展达到了这一点，它允许部分使用表现出热激活延迟荧光 (TADF) 的无重金属发射器来获得 100% 的最大内部量子效率。这种发射器也是新一代光学传感器的完美候选者，因为三重采集对不同的分析物（至少对氧气）很敏感。尽管迄今为止已经报道了许多有机 TADF 发射器作为 OLED 发射器，但对适用于 OLED 和光学传感器的材料的研究仍然极为罕见。

目标

为了在固态和三重态有机半导体中实现高光致发光量子产率，具有在蓝色 OLED 和光学传感器中应用所需的高效双极电荷传输，对称的供体-受体-供体有机发射体含有嘧啶-5-腈电子-本研究的主要目的是设计、合成和研究撤出支架和咔唑、叔丁基咔唑和甲氧基咔唑供体部分。

方法

新化合物通过多种实验方法进行了测试，包括光学和光电子能谱、飞行时间技术、电化学和热分析。

结果

展示了分子设计的优势，合成的发射器表现出天蓝色高效TADF，反向系统间交叉率超过10 ⁶ s ^-1，聚集诱导发射增强，固态光致发光量子产率超过50％，空穴和电子传输特性电荷迁移率超过 10 ^-4 cm ²/V·s，玻璃化转变温度达到 177 °C 时的玻璃形成特性。具有合成发射器的非掺杂发光层的天蓝色 OLED 的最大外部效率为 12.8%，而具有相同发射器的掺杂器件的最大外部效率为 14%。合成的发射器也用作光学传感器的氧气探针，其氧气敏感性由 Stern-Volmer 常数估计为 3.24·10 ^-5 ppm ^-1。

结论

开发的具有嘧啶-5-腈和咔唑部分的双极 TADF 发射器在蓝色 OLED 和光学传感器中均显示出有效的适用性。