Circularly polarized luminescence of a fluorescent chiral Binaphtylene-Perylenebiscarboxydiimide dimer
Circularly polarized luminescence of a fluorescent chiral Binaphtylene-Perylenebiscarboxydiimide dimer
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DOI：
10.1002/cphc.200600747
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发表时间：
2007-07-16
期刊：
影响因子：
2.9
通讯作者：
Nakashima, Takuya
中科院分区：
文献类型：
--
作者：
Kawai, Tsuyoshi;Kawamura, Kensuke;Nakashima, Takuya
圆偏振发光（CPL）是圆偏振光的各向异性发射，在各种有机分子和聚合物中得到了广泛的研究。[1]分子的CPL活性提供了关于激发态分子的光学手性的特定信息，而圆二色性（CD）提供了分子基态的结构信息。利用镧系离子的CPL对生物分子进行传感和探测已经得到了广泛的研究;在某些情况下会出现相当大的CPL不对称性，并且与手性有机和生物分子结合的发射的特定对映选择性猝灭也很普遍[2]。由于高度不对称的CPL材料潜在地适用于未来的信息和显示技术，已经研究了具有实质性光学活性的各种聚合物和自组织材料。手性液晶介质的荧光发射显示出显着的CPL不对称性，因为选择性反射的宏观结构与特定的螺旋节距尺度的光波长，这甚至作为一个手性激光腔。[3，4]一些具有手性结构的π-共轭聚合物也被报道表现出显着的CPL不对称性，甚至已经报道了圆偏振电致发光。[5-8]除了基于自组织分子和聚合物的CPL不对称性之外，在各向同性溶液相中已经提出了各种基于分子的本征CPL材料。[9]在早期的工作中，一些手性羰基化合物显示出具有相对较大的CPL不对称性的n-π* 发射。[10]研究了一系列具有π-π* 型荧光基团的手性聚合物，发现了基于手性激基复合物的CPL不对称性。[11]最近，已经提出了基于螺烯结构的高CPL活性分子。[12]然而，在大多数先前报道的情况下，CPL不对称性的增强导致荧光发射量子效率的降低，并且具有大CPL不对称性的CPL分子倾向于显示弱荧光发射。例如，螺烯和链内准分子的荧光量子效率可能小于50%。据我们所知，没有荧光量子产率大于80%的有机分子在溶液相中显示出大于2 × 10 - 3的CPL g因子;对这种分子的追求是非常有趣的，因为它将是CPL光谱学标准和未来CPL设备活性材料的理想候选者。在本研究中，CPL活性和高发射性分子被证明。通过先前报道的方法合成R和S分子结构如方案1所示的化合物1。[13]化合物1具有长的烷基链-所谓的“燕尾”-其能够在有机溶剂如氯仿和甲苯中溶解，并且具有两个彼此接近的荧光二萘嵌苯单元。[14]中心联萘部分促进了两个二萘嵌苯部分的手性结构和光学活性激子耦合。图1显示了1和参考化合物二萘嵌苯四羧基二烷基酰亚胺（2）的光学吸收和荧光发射光谱。在这两种分子中观察到对应于具有特征振动边带的苝单元的强吸收和发射带。这些吸收和发射光谱本质上与先前研究的分子相同。[13a]如Langhals所述，N，N ′-位上的烷基取代基不
Circularly polarized luminescence (CPL), which is anisotropic emission of circularly polarized light, has been studied extensively in various organic molecules and polymers.[1] CPL activity of the molecules provides specific information about optical chirality of the molecules in the excited state, whereas circular dichromism (CD) provides structural information of the ground state of the molecules. Sensing and probing for biological molecules with CPL of lanthanide ions have been widely investigated; considerably large CPL dissymmetry occurs in some cases and specific enantio-selective quenching of emission in combination with chiral organic and bio-molecules [2] is also prevalent. Since the highly dissymmetric CPL material is potentially applicable for future information and display technology, various polymeric and self-organized materials with substantial optical activity have been studied. Fluorescence emission from the chiral liquid crystal medium shows significant CPL dissymmetry because of selective reflection with the macroscopic structure with the specific helical pitch of scale of the optical wavelength, which even acts as a chiral lasing cavity.[3, 4] Some π-conjugated polymers with chiral structures have also been reported to exhibit remarkable CPL dissymmetry and even circularly polarized electroluminescence has been reported.[5–8] Beside the CPL dissymmetry based on the self-organized molecules and polymers, various molecular-based intrinsic CPL materials have been proposed in the isotropic solution phase.[9] In earlier works, some chiral carbonyl compounds have showed n–π* emission with relatively large CPL dissymmetry.[10] A variety of chiral polymers with π–π* type fluorescent groups have also been studied, in which characteristic CPL dissymmetry based on the chiral exciplex has been observed.[11] Much recently, highly CPL active molecules based on the helicene structure have been proposed.[12] In most previously reported cases, however, enhancement of the CPL dissymmetry results in a decrease in fluorescence emission quantum efficiency, and CPL molecules with large CPL dissymmetry tend to show weak fluorescence emission. For example, the fluorescence quantum efficiencies of the helicene and intra-chain excimers might be less than 50%. To the best of our knowledge, no organic molecule with fluorescence quantum yield larger than 80% shows a CPL g-factor larger than 2 10À3 in the solution phase; the quest for such a molecule is of great interest as it would be an ideal candidate as a standard for CPL spectroscopy and an active material for future CPL devices. In the present study, a CPL active and highly emissive molecule is demonstrated. Compound 1 whose R and S molecular structures are shown in Scheme 1 was synthesized by a previously reported method.[13] Compound 1 has long alkyl chains—so-called “Swallow-tails”—which enable solubility in organic solvents such as chloroform and toluene, and has two fluorescent perylene units which are close to each other.[14] The central binaphthylene moiety promotes chiral structure for the two perylene moieties and the optically active exciton coupling.Figure1 shows the optical absorption and fluorescence emission spectra of 1 and a reference compound perylenetetracarboxydialkylimide (2). Strong absorption and emission bands corresponding to the perylene units with characteristic vibrational side-bands are observed in both molecules. These absorption and emission spectra are intrinsically the same as those of the previously investigated molecule.[13a] As described by Langhals, alkyl substituent groups on N, N’-position does