Redox Switchable Photonic Materials Based on Organoimido-Polyoxometalate/Cyclodextrin Host-Guest Complexes

光子材料以有用和有趣的方式与光相互作用。它们使其能够被操纵，并转化为其他形式的能量。一类重要的光子材料是非线性光学（NLO）材料，其可用于操纵和调节激光光束的性质。例如，它们被用于通过从红外源产生二次谐波（SHG）来制造绿色激光器，以及用于将数字电子信号传输到光纤电信中的电光（EO）调制器。目前，大多数商业化的非线性光学材料是简单的无机盐。这些都是廉价，耐用，简单的SHG应用的理想选择。然而，在电信和计算中，它们的速度很慢，因为它们的响应源于（相对重的）离子响应于光的电场的位移。分子有机材料和金属有机材料承诺更快的响应，因为它们来自更轻、更快的电子的位移，以及合理的性质调谐和快速性质切换（即光学或电光晶体管的开/关）的可能性。但是，很难获得结合高NLO活性与足够的透明度和光稳定性的分子，并且增加在开/关状态之间可逆切换的能力是更大的挑战。最近，我们发现了一类有前途的新型分子非线性光学材料的基础上聚氧乙烯酸酯（POM）-一种类型的分子金属氧化物簇-连接到有机基团。这些基于POM的发色团（POMophores）具有小而稳定的有机基团和优异的透明度，可获得高的NLO系数，并显示出可用于切换NLO响应的氧化还原特性。该项目的下一阶段是将POMophores组装成可用于器件的块体材料-特别是EO调制器和晶体管。要做到这一点，我们必须找到一种方法来对齐所有的POMophore，使它们指向相同的方向，并产生净NLO效果。这是具有挑战性的，因为基于POM的材料的受控组装方法目前非常有限，为了实现这一目标，我们将开发一种新方法，首先将POMophore捕获在分子容器中。分子容器以这样的方式设计，即它们形成膜，其中所需的分子取向被强加在POMophore上。除了组织POM团以赋予本体NLO特性之外，容器还将在我们研究NLO响应的氧化还原开关时保护它们免受降解。POM提供了许多非线性光学之外的其他特性-例如，许多POM团簇是优秀的催化剂或光催化剂，因为它们能够快速接受和转移电子，一些具有磁性和/或发光性质，这是通过将合适的杂金属引入POM骨架中而引入的，并且POM也已显示出抗病毒活性。因此，我们预计化学和材料科学的其他领域将受益于使其封装和控制其在纳米尺度上的定位的方法。可能包括选择性催化，太阳能转换，记忆装置，甚至靶向生物/医学活性POM物质进行治疗干预。该项目将为此类开发奠定必要的基础，并可能生产未来电信和计算所需的新型高性能大块NLO材料。

Photonic materials interact with light in useful and interesting ways. They enable its manipulation, and conversion into other forms of energy. One important class of photonic materials are non-linear optical (NLO) materials, which can be used to manipulate and adjust the properties of laser light beams. For example, they are used to make green lasers by second harmonic generation (SHG) from an infra-red source, and in electro-optic (EO) modulators that transfer digital electronic signals into fibre-optic telecommunications. At present, most commercial NLO materials are simple inorganic salts. These are inexpensive, durable and ideal for simple SHG applications. However, in telecommunications and computing they suffer from slow speed, as their responses originate from displacement of (relatively heavy) ions in response to the electric field of light. Molecular organic and metal-organic materials promise faster responses, because they arise from displacement of lighter, faster electrons, and also rational property tuning and the possibility of rapid property switching (i.e. on/off for optical or electrooptical transistors). But it is difficult to obtain molecules combining high NLO activity with adequate transparency and photostability, and adding the ability to reversibly switch between on/off states is a still greater challenge. Recently, we discovered a promising new class of molecular NLO materials based on polyoxometalates (POMs) - a type of molecular metal oxide cluster - connected to organic groups. These POM-based chromophores (POMophores) obtain high NLO coefficients from materials with small, stable organic groups and excellent transparency, and show redox properties that could be used to switch the NLO response.The next stage, addressed in this project, is to assemble POMophores into bulk materials that can be used in devices - specifically EO modulators and transistors. To do this, we must find a way to align all of the POMophores so that they point in the same direction and give a net NLO effect. This is challenging, as methods for controlled assembly of POM-based materials are currently very limited, and to achieve the goal we will develop a new approach where we first trap the POMophore in a molecular container. The molecular containers are designed in such a way that they form a film where the desired molecular orientation is forced on the POMophore. In addition to organising the POMophores to give bulk NLO properties, the containers will also protect them from degradation when we investigate redox-switching of the NLO response.POMs offer many other properties beyond non-linear optics - for example many POM clusters are excellent catalysts or photocatalysts due to their ability to rapidly accept and transfer electrons, some have magnetic and/or luminescence properties introduced by incorporating suitable heterometals into the POM framework, and POMs have also demonstrated anti-viral activity. Therefore, we expect that other areas of chemistry and materials science will benefit from methods enabling their encapsulation and control over their positioning on the nanoscale. Possibilities could include selective catalysis, solar energy conversion, memory devices, and even targeting of biologically/medicinally active POM species for therapeutic interventions. This project will lay the groundwork necessary for such developments, as well as potentially producing the new, high performance bulk NLO materials needed for future telecommunications and computing.