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

光活性过渡金属配合物的开发是非常重要的，因为这些材料在过去几年中在许多应用中显示出巨大的潜力，包括生物成像，非线性光学，MEMS，太阳能电池和OLED。选定的有机过渡金属化合物现在已商业化用于移动的电话和其他平板显示器的OLED中。尽管显示技术的商业领域取得了进展，但在开发用于其他应用的光敏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。一个关键问题是单重态和三重态激发态的形成以及系统在这两种自旋态之间交叉的能力，这是一个通常被禁止的过程，但在金属原子存在的情况下可以成为允许的。这两种状态具有非常不同的性质，包括来自单线态的荧光和来自三线态的磷光和单线态氧敏化。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，即金属杂环戊二烯，这是很容易从简单的二炔前体以优异的产率制备，可以显示出意想不到的有效的荧光，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，反应可以同时产生异构的二苯并-金属杂环戊二烯，其显示出这类化合物中最高的磷光量子产率。为了理解和以可控的方式调节它们的高度不寻常的光学性质，需要进行基础研究。此外，令人惊讶的和非常令人兴奋的形成的两种异构体，显示完全不同的光学性质，一个荧光和一个磷光，激发态寿命相差5个数量级，需要一个系统的研究，以获得完全控制的反应途径，使这成为一个通用的路线，以获得非常有趣的二苯并-金属环戊二烯。我们还可能发现在某些条件下由其他新的二炔偶联过程形成的全新类型的产物。我们将制备各种此类化合物，并对其光学性质进行详细测量，结合理论研究，将深入了解其激发态的性质，使我们能够以受控的方式调整其性质。

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.