It is quite challenging to realize fluorescence resonance energy transfer (FRET) between two chromophores with specific positions and directions. Herein, through the self-assembly of two carefully selected fluorescent ligands via metal-coordination interactions, we prepared two tetragonal prismatic platinum(II) cages with reverse FRET process between their faces and pillars. Bearing different responses to external stimuli, these two emissive ligands are able to tune the FRET process, and thus making the cages sensitive to solvents, pressure and temperature. First, these cages could distinguish structurally similar alcohols such as n-butanol, t-butanol and i-butanol. Furthermore, they showed decreased emission with bathochromic shifts upon high pressure. Finally, they exhibited remarkable ratiometric response to the temperature in a wide range (223~353 K) with high sensitivity. For example, by plotting the ratio of the maximum emission (I600/I480) of metallacage 4b against the temperature, the slope reaches 0.072, which is among the highest values for ratiometric fluorescent thermometers reported so far. This work not only offers a strategy to manipulate the FRET efficiency in emissive supramolecular coordination complexes, but also paves the way for the future design and preparation of smart emissive materials with external stimuli responsiveness.

中文翻译：

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具有用于多重传感的反向荧光共振能量转移的发光铂 (II) 笼

在具有特定位置和方向的两个发色团之间实现荧光共振能量转移（FRET）是非常具有挑战性的。在此，通过金属配位相互作用对两个精心挑选的荧光配体进行自组装，我们制备了两个四方棱柱形铂 (II) 笼，它们的面和柱之间具有反向 FRET 过程。这两种发光配体对外部刺激有不同的反应，能够调整 FRET 过程，从而使笼子对溶剂、压力和温度敏感。首先，这些笼子可以区分结构相似的醇，例如正丁醇、叔丁醇和异丁醇。此外，它们在高压下显示出随着红移变化而减少的发射。最后，它们在宽范围（223~353 K）内对温度表现出显着的比率响应，具有高灵敏度。例如，通过绘制 metallacage 4b​​ 的最大发射率 (I600/I480) 与温度的比率，斜率达到 0.072，这是迄今为止报告的比率式荧光温度计的最高值之​​一。这项工作不仅提供了一种操纵发射超分子配位复合物中 FRET 效率的策略，而且为未来设计和制备具有外部刺激响应性的智能发射材料铺平了道路。