rISC - the game of strategic molecular design for high efficiency OLEDs

照明和显示器是我们日常生活的重要组成部分，消耗了全球约20%的电力。事实表明，夜间从太空可见的灯光是衡量一个国家经济发展的有效尺度，而通过开发吸收更多阳光的材料来捕获能源是减少我们对不可持续燃料来源依赖的核心。在产生光的背景下，有机发光二极管（OLED）是一种快速发展的技术，由于其潜在的高能效和在塑料基板上卷对卷印刷的能力，其非常有吸引力。然而，在效率方面，最初尝试实现基于纯有机材料的OLED受到发射光的激发态类型的限制。实际上，在电激发时，25%的发射分子处于发射单重激发态，而75%处于非发射三重激发态。然而，常规有机材料不能从三重激发态发射。该提案包括开发一类新的OLED，利用热激活延迟荧光（TADF）。在这里，三重态被热激活以变得与单重激发态等能，从而使有效的rISC成为辐射单重态歧管。在TADF材料中必须克服的主要挑战之一是，使用纯有机材料意味着单线态和三线态之间通常较弱的自旋轨道耦合可以导致延伸到毫秒范围内的rISC速率。这导致在较高电流密度下器件效率的不良滚降。然而，通过TADF分子的新概念设计，我们已经表明可以实现> 1 E7 s-1的反向系间穿越（rISC）速率和单位光致发光量子产率（PLQY），这是以前认为站不住脚的组合。计算和生物物理研究，以开发利用空间位阻和非空间位阻的方法。共价相互作用以施加激发态动力学的更精细构象控制，从而增强功能性质。这是结合详细的研究进行，以建立一个更深入的了解激发态和电荷复合形成的几何形状。该提案将提供关于TADF OLED中的发射过程以及如何将rISC速率提高到超过1 E8 s-1同时保持PLQY ~ 1的新理解。实现这些成果将对OLED行业产生重大的颠覆性影响，并确保英国继续留在利润丰厚的OLED材料供应链中。

Lighting and displays form essential parts of our daily lives and consume approximately 20% of the electricity used worldwide. It has been shown that lights visible from space at night time are an effective measure of a country's economic development, while energy capture through the development of materials that absorb more sunlight is at the heart of attempts to reduce our reliance upon unsustainable fuel sources. In the context of generating light, Organic Light Emitting Diodes (OLEDs) are a rapidly expanding technology which are highly appealing owing to their potential high energy efficiency and ability to be printed roll-to-roll on a plastic substrate. However, in terms of efficiency, initial attempts to implement OLEDs based upon purely organic materials were restricted by the type of excited state which emits the light. Indeed, upon electrical excitation 25% of the emitting molecules are in emissive singlet excited state, whilst 75% are in non-emissive triplet excited states. However, conventional organic materials cannot emit from the triplet excited states. The proposal consists of developing a new class of OLEDs that exploits thermally activated delayed fluorescence (TADF). Here a triplet state is thermally activated to become iso-energetic with a singlet excited state, enabling efficient rISC into a radiative singlet manifold. One of the major challenges that must be overcome in TADF materials is that the use of pure-organic materials means that the often weak spin-orbit coupling between the singlet and triplet states can lead to rISC rates that extend into the millisecond range. This causes poor roll-off in device efficiency at higher current densities. However, through a new conceptual design of TADF molecules, we have shown that it is possible to achieve both a reverse intersystem crossing (rISC) rate > 1E7 s-1 and a unity photoluminescence quantum yield (PLQY), a combination previously considered untenable.In this proposal we will combine detailed synthetic, computational and photophysical studies to develop approaches for exploiting steric hindrance and non-covalent interactions to exert finer conformational control of the excited state dynamics to enhance functional properties. This is performed in conjunction with detailed studies to establish a deeper understanding of the excited states and their geometries formed by charge recombination. This proposal will deliver new understanding about the emission processes in TADF OLEDs and how to enhance the rISC rate to beyond 1E8 s-1 whilst retaining PLQY ~ 1. Achieving these outcomes will have a major disruptive impact on the OLED industry and ensure that the UK remains in the lucrative OLED materials supply chain.