Presented here is the study of a new example of [4]cyclofluorene, with ethyl chains on the bridgeheads. Its molecular structure was established by solution NMR spectroscopy and single-crystal X-ray diffraction. Three successive oxidation processes and one reversible reduction were observed through cyclic voltammetry. The optical properties were characterized both in solution and thin film by UV/visible spectroscopy as well as stationary and time-resolved fluorescence. It was found that this [4]cyclofluorene displays different characteristics compared with the other [4]cyclofluorenes substituted by methyl or propyl chains: a simple modification of the chain length induces a non-negligible effect on the emission properties, which must be linked to the specific arrangement of the fluorene units. Furthermore, single-crystal X-ray diffraction reveals the formation of a pseudo-tubular solid-state arrangement of fully symmetrical ring structures, which was not observed for the other members of the [4]cyclofluorenes family. This finding could open the way to modulation of properties of cyclofluorenes through alkyl chain engineering.

中文翻译：

---

[4]环芴：烷基链长的意外影响。

这里介绍的是对[4]环芴的一个新实例的研究，该化合物在桥头上带有乙基链。通过溶液NMR光谱和单晶X射线衍射确定其分子结构。通过循环伏安法观察到三个连续的氧化过程和一个可逆的还原。通过紫外/可见光谱在溶液和薄膜中以及在固定和时间分辨的荧光中表征了光学性质。发现与其他被甲基或丙基链取代的[4]环芴相比，[4]环芴显示出不同的特性：对链长的简单修饰对发射性能产生不可忽略的影响，必须将其与芴单元的具体排列。此外，单晶X射线衍射揭示了完全对称的环状结构的伪管状固态排列的形成，这在[4]环芴家族的其他成员中没有观察到。这一发现可以为通过烷基链工程调节环芴的性质开辟道路。