Switching Between Fluorescence and Phosphorescence - Synthesis and Optical Properties of Metallacyclopentadienes

光活性过渡金属络合物的开发具有重要意义，因为这类材料在生物成像、非线性光学、光催化、太阳能电池和有机发光二极管等领域显示出巨大的应用潜力。选定的有机过渡金属化合物现在被用于手机和其他平板显示器的有机发光二极管中。尽管在商业显示技术领域取得了进展，但在开发用于其他应用的光活性过渡金属化合物之前，仍然存在许多挑战和额外的基础研究。一个关键问题是单态和三态激发态的形成，以及系统在这两个自旋态之间交叉的能力，这一过程通常是被禁止的，但在金属原子存在的情况下可以成为允许的过程。这两个态具有非常不同的性质，包括来自单态的荧光和来自三态的磷光和单态氧敏化。它们不同的寿命也允许其他应用，例如，涉及电荷分离或复合。因此，了解这些状态之间的系统间交叉是相当重要的。我们最近发现，一类有机金属化合物，即金属环戊二烯，可以很容易地从简单的二炔前驱体中制备出来，并且可以显示出出人意料的高效荧光而不是磷光。此外，初步结果表明，通过改变金属前体上的配体，反应可以同时生成异构型二苯并金属环戊二烯，这些异构体显示出这类化合物最高的磷光量子产率。我们设想了我们的化合物的几个潜在应用，但要实现这些应用，需要进行基础研究，以便以受控的方式理解和调制它们非常不寻常的光学性质。此外，两种异构体的形成令人惊讶和非常兴奋，这两种异构体表现出完全不同的光学性质，一个荧光的和一个磷光的，激发态寿命相差5个数量级，需要进行系统的研究来完全控制反应途径，使这成为获得高度感兴趣的二苯并金属环戊二烯的一般路线。在一定条件下，我们还可以发现由其他新的联炔偶联工艺形成的全新产品类型。我们将制备各种类型的化合物，并对它们的光学性质进行详细的测量，结合理论研究，将提供对它们激发态性质的见解，使我们能够以可控的方式调整它们的性质。

The development of photoactive transition metal complexes is of great importance, as such materials have shown immense potential in the last few years for many applications including biological imaging, non-linear optics, photocatalysis, solar cells and OLEDs. Selected organo-transition metal compounds are now employed commercially in OLEDs for mobile phones and other flat panel displays. Despite the progress in the commercial field of display technology, there are still many challenges and additional fundamental studies are required prior to the development of photoactive transition metal compounds for other applications. One key issue is the formation of singlet and triplet excited states and the ability of a system to cross between these two spin states, a process which is normally forbidden, but can become allowed in the presence of a metal atom. These two states have very different properties, including fluorescence from singlets and phosphorescence and singlet oxygen sensitization from triplets. Their different lifetimes also allow for other applications which, for example, involve charge separation or recombination. It is thus of considerable important to understand intersystem crossing between these states.We have recently discovered that a class of organometallic compounds, namely metallacyclopentadienes, which are easy to prepare in excellent yield from simple diyne precursors, can display unexpectedly efficient fluorescence rather than phosphorescence. In addition, preliminary results show that by changing the ligands on the metal precursor, the reactions can simultaneously generate isomeric dibenzo-metallacyclopentadienes which display amongst the highest phosphorescence quantum yields for this class of compounds.We envisage several potential applications of our compounds, but to realize them, fundamental studies are required in order to understand and modulate their highly unusual optical properties in a controlled fashion. In addition, the surprising and very exciting formation of two isomers which display completely different optical properties, one fluorescent and one phosphorescent, with excited state lifetimes differing by 5 orders of magnitude, requires a systematic study to gain full control of the reaction pathway making this a general route to access highly interesting dibenzo-metallacyclopentadienes. We may also discover entirely new types of products formed by other novel diyne coupling processes under certain conditions. We will prepare a wide range of these types of compounds and make detailed measurements of their optical properties which, in combination with theoretical studies, will provide insights into the nature of their excited states, allowing us to tune their properties in a controlled manner.