Thermochromism is an optical property wherein color changes dramatically during a phase transition. An effective way to realize thermochromism is to manipulate emission properties depending on supramolecular interactions, and this can be achieved in the bulk state. Herein, we report the lateral chain length-dependent photoluminescence (PL) behavior of non-polycyclic luminogens in the crystalline (Cry) and liquid (Liq) phases. Under UV-irradiation at 365 nm, the emission color of 1, which has shorter tri (ethylene oxide) chains, changed remarkably from sky-blue to blue color upon melting, while that of 2, which has longer poly (ethylene oxide) (PEO) chains, remained blue regardless of the melting transition. Interestingly, dual emission near 400 nm and 515 nm was observed in the Cry phase of 1, whereas emission was observed only near 400 nm in the Cry phase of 2. Upon melting, both compounds emitted near 400 nm. PL and excitation spectra revealed that the emission at 400 nm and 515 nm originated from short- and long-ranged electronically coupled species (SRECS and LRECS), respectively. Notably, efficient fluorescence resonance energy transfer (FRET) from SRECS to LRECS occurred in the Cry phase of 1. Dielectric relaxation spectroscopy analysis indicated that the degree of electronic coupling of aromatic luminogens was closely associated with their rotational dynamics. The rotational motion was fully restricted in the Cry phase of 1, whereas it was activated in the Cry phase of 2. The different rotational dynamics were attributed to the different lengths of the lateral chain, which influenced the degree of electronic coupling in the Cry phase and endowed thermochromism in the non-polycyclic luminogens.

热致变色是一种光学特性，其中颜色在相变期间显着变化。实现热致变色的一种有效方法是根据超分子相互作用来控制发光特性，这可以在本体状态下实现。在此，我们报告了非多环发光体在结晶 (Cry) 和液态 (Liq) 相中的侧链长度依赖性光致发光 (PL) 行为。在 365 nm 的紫外线照射下，具有较短三（环氧乙烷）链的1的发射颜色在熔化时从天蓝色显着变为蓝色，而2，具有较长的聚（环氧乙烷）（PEO）链，无论熔化转变如何都保持蓝色。有趣的是，在1的 Cry 阶段观察到 400 nm 和 515 nm 附近的双发射，而在2的 Cry 阶段仅在 400 nm 附近观察到发射。熔化后，两种化合物都在 400 nm 附近发射。PL 和激发光谱显示 400 nm 和 515 nm 的发射分别来自短程和长程电子耦合物质（SRECS 和 LRECS）。值得注意的是，从 SRECS 到 LRECS 的高效荧光共振能量转移 (FRET) 发生在1的 Cry 阶段. 介电弛豫光谱分析表明，芳香族发光体的电子耦合程度与其旋转动力学密切相关。旋转运动在1的 Cry 阶段被完全限制，而它在2的 Cry 阶段被激活。不同的旋转动力学归因于侧链的不同长度，这影响了Cry相中的电子耦合程度并赋予了非多环发光体中的热致变色性。