物理化学学报 >> 2024, Vol. 40 >> Issue (8): 2307024.doi: 10.3866/PKU.WHXB202307024

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含Benzo[a]azulene单元的锯齿状梯形共轭聚合物的表面在位合成

吴名辉1, MühlinghausMarkus2, 李雪超1, 徐超婕1, 陈强1, 张海明1, MüllenKlaus2,*(), 迟力峰1,*()   

  1. 1 江苏省碳基功能材料与器件重点实验室, 苏州大学功能纳米与软材料研究院, 江苏 苏州 215123
    2 马克斯·普朗克高分子研究所, 美因茨 55128, 德国
  • 收稿日期:2023-07-12 修回日期:2023-09-08 录用日期:2023-09-18 发布日期:2023-09-22
  • 通讯作者: Email: chilf@suda.edu.cn (迟力峰)muellen@mpip-mainz.mpg.de (Klaus Müllen)
  • 基金资助:
    国家自然科学基金(51821002); 国家自然科学基金(22072103); 国家自然科学基金(22161132026); 苏州纳米科技协同创新中心; 江苏省高等学校重点学科建设项目(PAPD); 高等学校学科创新引智计划(“111”计划); 江苏省卓越博士后计划

On-Surface Synthesis of Chevron-Shaped Conjugated Ladder Polymers Consisting of Benzo[a]azulene Units

Minghui Wu1, Markus Mühlinghaus2, Xuechao Li1, Chaojie Xu1, Qiang Chen1, Haiming Zhang1, Klaus Müllen2,*(), Lifeng Chi1,*()   

  1. 1 Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University, Suzhou 215123, Jiangsu Province, China
    2 Max Planck Institute for Polymer Research, Mainz 55128, Germany
  • Received:2023-07-12 Revised:2023-09-08 Accepted:2023-09-18 Published:2023-09-22
  • Contact: Email: chilf@suda.edu.cn (Lifeng Chi)muellen@mpip-mainz.mpg.de (Klaus Müllen)
  • Supported by:
    the National Natural Science Foundation of China(51821002); the National Natural Science Foundation of China(22072103); the National Natural Science Foundation of China(22161132026); the Collaborative Innovation Center of Suzhou Nano Science & Technology; the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD); the 111 Project(“111”计划); the Jiangsu Funding Program for Excellent Postdoctoral Talent

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摘要：

梯形共轭聚合物(CLPs)因其独特的光电性质而受到广泛关注。绝大多数CLPs是通过溶液方法合成的，但近年来，在超高真空环境中进行的表面原位合成策略逐渐崭露头角，成为CPL合成的新方法。表面原位合成方法能够克服传统溶液合成的限制，如随着聚合度增加而受限的溶解度和结构稳定性，从而实现复杂共轭结构的精确合成。Azulene衍生物是在表面合成非苯型CLPs的有吸引力的前体。与传统的只含六元环的CLPs相比，使用烷基取代的azulene作为前体分子，有望获得具有复杂骨架结构的CLPs，从而调控其电子性质，但目前很少有人探索这种策略。本文报道了3,3'-二溴-2,2’-二甲基-1,1’-联薁(DBMA)在Au(111)表面上的热化学反应。在室温的Au(111)衬底上，我们发现沉积的分子在重构表面的fcc (面心立方堆积)区域形成无定型的聚集体，并在100 ℃以下保持形貌不变。当退火温度高于150 ℃后，DBMA发生脱溴反应并与金原子络合形成具有复杂空间立体结构的2,2’-二甲基-1,1’-联薁有机金属聚合物，并展现出迥异的图像特征。随后在更高温度下退火，有机金属聚合物脱去金属原子并经历碳碳偶联反应。该过程伴随着甲基与相邻薁单元之间的分子内环化反应，形成了含有benzo[a]azulene单元的梯形共轭聚合物。有趣的是，我们发现当一侧甲基参与反应并在聚合物中形成六元环时，会显著地弯折聚合物链，使得另一侧甲基与薁单元之间的距离增加，并抑制预期的环化过程。我们通过键分辨扫描探针显微镜对反应过程中的相关结构进行了研究，发现反应结果与反应中间结构的应力关联紧密。我们的结果表明，烷基取代的azulene前体可应用于非苯型碳纳米结构的表面合成，并有望实现扩展的非苯型二维碳纳米结构。

关键词: 表面在位合成, 薁, 非苯型碳纳米结构, 梯形共轭聚合物, 扫描探针显微镜, 键分辨原子力显微镜

Abstract:

Conjugated ladder polymers (CLPs) have attracted broad interest due to their intriguing optical and electronic properties. While many of these CLPs have been synthesized using solution-based reactions, on-surface synthesis under high vacuum conditions has gradually gained prominence in recent decades. This new approach holds promise for overcoming some of the limitations of conventional solution-based methods, such as the low solubility and stability of newly formed large π-conjugated systems. Azulene derivatives are attractive precursors for on-surface synthesis of CLPs that incorporate non-benzenoid moieties. The use of alkyl-substituted azulene precursors shows potential in providing CLPs with more complex backbone structures and modulated electronic properties compared to traditional CLPs that containing solely of six-membered rings. However, this strategy has been scarcely explored to date. In this study, we report on the thermal reactions of 3,3'-dibromo-2,2'-dimethyl-1,1'-biazulenyl (DBMA) on Au(111) surfaces. At room temperature, we observed that the deposited molecules formed amorphous aggregates in the fcc (face center cubic) regions of the reconstructed Au(111) surface, remaining unchanged below 100 ℃. Debromination of DBMA was induced above 150 ℃, leading to the formation of 1,1'-biazulenyl-2,2'-dimethyl-3,3'-diyls-Au organometallic polymers. These polymers exhibited complex stereostructures and distinct imaging features. At higher temperatures, the organometallic polymer underwent C―C coupling, followed by dehydrocyclization between the methyl groups and the adjacent azulene units, resulting in the ladder polymer containing benzo[a]azulene units. Interestingly, we observed that the formation of hexagonal rings between the methyl groups and the adjacent azulene units caused the polymeric chain to bend, increasing the distance between the corresponding reaction sites (methyl group and azulene) on the other side of the polymer chain. Due to the ring strain, the second ring closure did not occur within the azulene dimer as expected. Instead, this methyl group cyclized toward the other azulene unit, resulting in CLPs with a chevron shape and the absence of long-range periodicity. The evolution of related chemical species and the structures of CLPs were analyzed using scanning tunneling microscopy (STM) and bond-resolved atomic force microscopy (BR-AFM), and the reaction mechanism was discussed. This study thus demonstrates the feasibility of utilizing alkyl-substituted azulenic precursors in the synthesis of non-benzenoid carbon nanostructures on surfaces and suggests the possibility of developing two-dimensional nanostructures containing non-benzenoid units through on-surface azulene chemistry.

Key words: On-surface synthesis, Azulene, Non-benzenoid carbon nanostructure, Conjugated ladder polymer, Scanning probe microscopy, Bond-resolved atomic force microscopy