Oligo- and Polyfluorenes Meet Cellulose Alkyl Esters: Retention, Inversion, and Racemization of Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD) via Intermolecular C-H/O=C Interactions
Oligo- and Polyfluorenes Meet Cellulose Alkyl Esters: Retention, Inversion, and Racemization of Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD) via Intermolecular C-H/O=C Interactions
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DOI：
10.1021/acs.macromol.6b02762
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发表时间：
2017-03-14
期刊：
影响因子：
5.5
通讯作者：
Fujiki, Michiya
中科院分区：
文献类型：
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作者：
Guo, Sibo;Suzuki, Nozomu;Fujiki, Michiya
由于不带电分子和聚合物的无限分子内和分子间旋转自由度，检测它们之间的手性/螺旋相互作用是困难的。为了阐明从手性聚合物到不带电荷的非手性分子的手性和/或螺旋度转移，我们选择刚性三乙酸纤维素（CTA）和乙酸丁酸纤维素（CABu）作为非发色螺旋/手性聚合物。在这里，我们强调了刚性9，9-二烷基芴低聚物和聚合物（重复数n = 1，2，3，5，7，47，201）作为非手性发色团发光体。这些芴揭示了明确的圆偏振发光（CPL）和双信号圆二色性（CD）信号时，嵌入CTA和CABu膜。在基态，当n = 1-7时，CTA和CABu共同诱导（+）-CD信号，而当n >= 47时，它们分别诱导（+）-和（-）-CD信号。在光激发态，当n >= 3时，CTA和CABu分别诱导（+）-和（-）-CPL信号。在比较基态和光激发态时，当n = 2-7时，CABu诱导（+）-CD和（-）-CPL信号，而当n >= 3时，CTA诱导相同的（+）-CD和（+）-CPL信号。D-葡萄糖手性和主链螺旋性之间的冲突被认为是造成这些异常的原因，因为CTA和CABu尽管是β（1 -> 4）-连接的D-葡萄糖残基的共同框架，但分别优选左手和右手螺旋性。分子力学/分子动力学模拟表明H-C（由于二辛基芴的亚甲基）和O=C（由于CTA的D-葡萄糖上连接的乙酰基）之间存在分子间C-H/O=C相互作用。该模拟通过在C-13=O（Δ c = 170.6ppm，CTA）处的清晰交叉峰的第一次检测得到证实，并且发现CH 2质子（Δ（H）= 2.55ppm，芴，n = 201）表示根据固态H-1-C-13 HETCOR NMR光谱的相位调制的Lee- Goldburg同素脱耦的最短C-H-1/O=C-13距离。此外，在CTA中的光学活性芴的实时CPL/PL振幅测量中的第一个光致变化揭示了手光学状态的稳定性随着n的增加而增加，并且当n >= 47时保持不变。
Detecting chiral/helical interactions among noncharged molecules and polymers is difficult due to their unlimited intra- and intermolecular rotational freedom. To clarify the chirality and/or helicity transfer from a chiral polymer to noncharged achiral molecules, we chose stiff cellulose triacetate (CTA) and cellulose acetate butyrate (CABu) as nonchromophoric helical/chiral polymers. Here, we highlighted stiff 9,9-dialkylfluorene oligomers arid polymers (repeating number n = 1, 2, 3, 5, 7, 47, 201) as achiral chromophoric luminophores. These fluorenes revealed clear circularly polarized luminescence (CPL) and bisignate circular dichroism (CD) signals when embedded into CTA and CABu films. In the ground state, when n = 1-7, CTA and CABu commonly induced (+)-CD signals, whereas when n >= 47, they induced (+)- and (-)-CD signs, respectively. In the photoexcited state, when n >= 3, CTA and CABu induced (+)- and(-)-CPL signs, respectively. Upon comparing the ground and photoexcited states, when n = 2-7, CABu induced (+)-CD and (-)-CPL signs, whereas when n >= 3, CTA induced the same (+)-CD and (+)-CPL signs. A conflict between the D-glucose chirality and main-chain helicity was assumed to be responsible for these anomalies because CTA and CABu, despite being common frameworks of beta(1 -> 4)-linked D-glucose residues, prefer left- and right-handed helicities, respectively. Molecular mechanics/molecular dynamics simulations suggested intermolecular C-H/O=C interactions between H-C (due to the methylene group of the dioctylfluorenes) and O=C (due to the acetyl group attached to the D-glucose of CTA). This simulation was confirmed by the first detection of a clear cross-peak at C-13=O (delta c = 170.6 ppm, CTA) and the finding CH2 protons (delta(H) = 2.55 ppm, fluorene with n = 201) represented the shortest C-H-1/O=C-13 distance according to the phase-modulated Lee- Goldburg homonuclear decoupling of solid-state H-1-C-13 HETCOR NMR spectroscopy. Moreover, the first photoinduced change in the real-time CPL/PL amplitude measurement of optically active fluorenes in CTA revealed that the stability of the chiroptical state increases as n increases and remains unchanged when n >= 47.