Helix Induction to Polyfluorenes Using Circularly Polarized Light: Chirality Amplification, Phase-Selective Induction, and Anisotropic Emission
Helix Induction to Polyfluorenes Using Circularly Polarized Light: Chirality Amplification, Phase-Selective Induction, and Anisotropic Emission
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DOI：
10.1021/acs.macromol.8b01453
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发表时间：
2018-09-11
期刊：
影响因子：
5.5
通讯作者：
Nakano, Tamaki
中科院分区：
文献类型：
--
作者：
Wang, Yue;Harada, Takunori;Nakano, Tamaki
主要使用膜样品，彻底研究了使用圆偏振光（CPL）对聚（9，9-二辛基芴-2，7-二基）（聚（DOF））、聚（9，9-二十二烷基芴-2，7-二基）（聚（DDF））和聚（9，9-二己基芴-2，7-二基）（聚（DHF））的手性诱导（优选手螺旋诱导）。我们发现，β相的存在是必不可少的手性诱导聚（自由度），这表明链间相互作用的重要性，手性诱导首先发生在β相，然后扩展到α相。通过在β相吸收带（435 nm）处照射或短时间照射全波长范围，仅对β相进行手性诱导，而对于不含β相的聚（DHF），使用非手性辅助分子诱导纯α相手性。手性诱导对于具有辛基和十二烷基链的聚合物，聚（DOF）和聚（DDF）是可行的，而对于具有己基链的聚合物，聚（DHF）是不可能的，除非使用辅助分子。CPL驱动的手性诱导发生通过对映体选择性光激发的右和左手扭曲的二联体组成的聚合物链成非手性，共面构象，和失活的共面构象导致右和左手扭曲的二联体。手性放大通过共面构象优先于手的偏向失活而发生，这与附近的“预形成的单手二联体或更长链”的失活相同（“失活手性放大”）。此外，基于手性诱导过程中的温度效应，还提出了“基态手性放大”的概念。如果在室温下储存而不受强光照射，薄膜样品诱导的手性结构是稳定的。光学活性聚（DOF）薄膜显示出高效的圆偏振发光。
Chirality induction (preferred-handed helix induction) to poly(9,9-dioctylfluorene-2,7-diyl) (poly(DOF)), poly(9,9-didodecylfluorene-2,7-diyl) (poly(DDF)), and poly(9,9-dihexylfluorene-2,7-diyl) (poly(DHF)) using circularly polarized light (CPL) was thoroughly investigated mainly using film samples. We found that the presence of the beta-phase is indispensable in chirality induction to poly(DOF) which suggests the importance of interchain interactions and that chirality induction first occurs preferentially in the beta-phase and then extended to the alpha-phase. Chirality induction only to the beta-phase was attained by irradiating at the beta-phase absorbance band (435 nm) or by irradiating the full wavelength range for a short time while pure alpha-phase chirality is induced for poly(DHF) having no beta-phase using an achiral aid molecule. Chirality induction is feasible for polymers having octyl and dodecyl chains, poly(DOF) and poly(DDF), whereas it is not possible for the polymer having a hexyl chain, poly(DHF), unless an aid molecule is used. CPL-driven chirality induction occurs through enantiomer-selective photoexcitation of either a right- and left-handed twisted diad composing the polymer chain into achiral, coplanar conformation, and deactivation of the coplanar conformation leading to right- and left-handed twisted diads. Chirality amplification takes place through biased deactivation of coplanar conformation preferentially to the hand which is the same as that of "preformed single-handed diad or longer chain" in the vicinity ("deactivation chirality amplification"). In addition, "ground-state chirality amplification" is also proposed on the basis of significant temperature effects in chirality induction. Chiral structure induced to the film samples is stable if they are stored at room temperature without irradiation with intense light. Optically active poly(DOF) films showed efficient circularly polarized luminescence.