Thermal expansion, the response in shape, area or volume of a solid with heat, is usually large in molecular materials compared to their inorganic counterparts. Resulting from the intrinsic molecule flexibility, conformational changes or variable intermolecular interactions, the exact interplay between these mechanisms is however poorly understood down to the molecular level. Here, we investigate the structural variations of a two-dimensional supramolecular network on Au(111) consisting of shape persistent polyphenylene molecules equipped with peripheral dodecyl chains. By comparing high-resolution scanning probe microscopy and molecular dynamics simulations obtained at 5 and 300 K, we determine the thermal expansion coefficient of the assembly of 980 ± 110 × 10⁻⁶ K⁻¹, twice larger than other molecular systems hitherto reported in the literature, and two orders of magnitude larger than conventional materials. This giant positive expansion originates from the increased mobility of the dodecyl chains with temperature that determine the intermolecular interactions and the network spacing.

与无机材料相比，分子材料中的热膨胀（固体在形状，面积或体积方面的响应）通常较大。由于固有的分子柔韧性，构象变化或可变的分子间相互作用，这些机制之间的确切相互作用直到分子水平才被人们了解。在这里，我们调查的二维超分子网络在Au（111）上的结构变化，该结构由带有外围十二烷基链的形状持久性聚亚苯基分子组成。通过比较高分辨率扫描探针显微镜和在5和300 K下获得的分子动力学模拟，我们确定了组件的热膨胀系数为980±110×10 ^-6  K ^-1，比迄今为止文献中报道的其他分子系统大两倍，并且比常规材料大两个数量级。这种巨大的正膨胀源自十二烷基链随温度的增加而增加，该温度决定了分子间的相互作用和网络间距。