摘要/Abstract
设计合成了以乙氧基柱[5]芳烃为环状分子，萘二酰亚胺衍生物为线性分子的[3]轮烷（[3]R和[3]R'）.其分离产率分别达到45%和62%.利用核磁氢谱和碳谱、二维旋转Overhause波谱（ROESY）以及高分辨质谱等对[3]R和[3]R'的轮烷结构进行了详细表征，并系统研究了轮烷分子的紫外吸收和荧光光谱.由于两侧大体积的乙氧基柱[5]芳烃阻止了[3]轮烷在高浓度下芳香环的过密堆积，使得[3]R和[3]R'即使在固体状态下都可以发射明亮的红色荧光.推测该轮烷分子在发光材料、光电器件等方面有潜在应用，同时本研究也对高效固体发光分子的制备提供了新思路.
关键词: 轮烷, 柱芳烃, 荧光, 萘二酰亚胺
Rotaxanes, composed of macrocyclic wheel and linear axle, have been used in areas such as molecular machines, stimuli-responsive materials, information storage, supramolecular catalysts. The macrocyclic host and its noncovalent interaction are key for the rotaxanes. Pillar[n]arenes (n=5~10) have drew much attention as widely-used hosts. Their facile synthesis, unique rigid structure, versatile functionalization, and interesting host-guest properties enable pillar[n]arenes to build various supramolecular architectures including rotaxanes. Currently, the research of pillararene-based rotaxanes mainly focuses on the synthesis, the responsiveness to temperature and solvent, and the application as catalyst, however, reports of emissive pillararene-based rotaxanes are very rare. Besides, higher-ordered[n]rotaxanes (n ≥ 3) based on pillararene remain rarely explored limited by the poor synthetic yield, despite their fascinating structure and potential applications in molecular devices. Herein, we report two pillararene-based rotaxanes ([3]R and [3]R') incorporating naphthalene diimide with red fluorescence in solid state. The 1,4-diethoxypillar[5]arene (EtP5A) was chosen as the wheel, diamino-substituted naphthalene diimides (NDI) were used as the axle containing two separated linear guest parts for EtP5A. The addition reaction of NDI-precursor S1/S2 and the stopper 3,5-dimethylphenyl isocyanate with the presence of EtP5A afforded [3]R and[2]R (byproduct as model compound)/[3]R', respectively, with high yield of 45% for [3]R and 62% for [3]R'. The structures of rotaxanes were confirmed by 1H NMR spectroscopy, ROESY (rotating frame Overhause enhancement spectroscopy), and HR-ESI-MS. Limited by the length of linear chains, EtP5As are adjacent tightly to NDI in [3]R, whereas EtP5As stay four-atom distance away from NDI in 3[R]'. The optical properties of rotaxanes in various solvents and in powders were detected. [3]R and [3]R' show bright red fluorescence not only in solution but also in solid state, which distinguishes [3]R and [3]R' from [2]R and most of NDI-based fluorescent compounds. The increased fluorescence in solid state of [3]R and [3]R' benefits from the bulky EtP5As hindering the π-π interaction and suppressing the self-quenching of NDI. We suspect that [3]R and [3]R' may have potential applications in red-emitting materials and optoelectronic devices.
Key words: rotaxane, pillararene, fluorescence, naphthalene diimide
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