Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-2136, USA.
J Am Chem Soc. 2013 Aug 21;135(33):12259-69. doi: 10.1021/ja4043092. Epub 2013 Aug 9.
Silsesquioxanes (SQs) are of considerable interest for hybrid electronic and photonic materials. However, to date, their photophysical properties have not been studied extensively, thus their potential remains conjecture. Here we describe the first known efforts to map structure-photophysical properties as a function of cage symmetry and size by comparing identically functionalized systems. Our focus here is on the solution photophysical properties of the title stilbenevinyl-SQs, which were characterized using single photon absorption, two-photon absorption, fluorescence emission, and fluorescence lifetime kinetics. We offer here the first detailed photophysical study of the larger pure T10 and T12 silsesquioxanes and show photophysical properties that differ as a function of size, especially in their fluorescence behavior, indicating that cage size and/or symmetry can strongly affect photophysical properties. We also find that they offer excitation-dependent emission (evidence of rare "red-edge" effects). The T10 stilbenevinyl-SQ offers up to a 10-fold increase in two-photon absorption cross section per chromophore over a free chromophore, signifying increased electronic coupling. The SQ cage compounds show "rise times" of 700-1000 fs and low anisotropy (~0.1) in fluorescence lifetime kinetic studies. These results indicate excited state energy transfer, unobserved for the free chromophores and unexpected for systems with "inert" silica cores and for 3-D hybrid molecular species. These findings provide the first detailed photophysical study of chromophore-functionalized T10 and T12 silsesquioxanes and show that SQs may be considered a separate class of compounds/materials with anticipated novel properties of value in developing new components for electronic and photonic applications.
倍半硅氧烷（Silsesquioxanes，简称 SQs）在混合电子和光子材料方面具有重要的应用价值。然而，迄今为止，它们的光物理性质尚未得到广泛研究，因此其潜在应用仍存在争议。在本文中，我们首次尝试通过比较具有相同功能的系统，来描绘结构-光物理性质与笼对称性和尺寸的关系。我们的研究重点是标题化合物的溶液光物理性质，通过单光子吸收、双光子吸收、荧光发射和荧光寿命动力学等方法对其进行了表征。我们首次详细研究了较大的纯 T10 和 T12 倍半硅氧烷的光物理性质，结果表明其光物理性质随尺寸变化而变化，尤其是在荧光行为方面，这表明笼的尺寸和/或对称性可能会强烈影响光物理性质。我们还发现它们具有激发依赖性的发射（罕见的“红色边缘”效应的证据）。与自由发色团相比，T10 苯乙烯基倍半硅氧烷的每个发色团的双光子吸收截面增加了 10 倍，这表明电子耦合增强。笼状化合物的荧光寿命动力学研究显示出“上升时间”为 700-1000fs，各向异性低（~0.1）。这些结果表明，在自由发色团中未观察到的激发态能量转移，对于具有“惰性”二氧化硅核和 3-D 混合分子的系统来说是出乎意料的，这在 SQs 中得到了证实。这些发现提供了对 T10 和 T12 倍半硅氧烷的首次详细光物理研究，并表明 SQs 可能被视为一类具有预期新型性质的化合物/材料，可用于开发电子和光子应用的新型组件。
