物理化学学报 >> 2019, Vol. 35 >> Issue (6): 637-643.doi: 10.3866/PKU.WHXB201807004

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通过增强电荷转移激发态构建激发态下稳定的基于氰基二苯乙烯的E/Z构型

董玉杰,许晨东,王士昭,李维军,宋庆宝*(),张诚*()   

  • 收稿日期:2018-07-04 出版日期:2018-10-31 发布日期:2018-10-31
  • 通讯作者: 宋庆宝,张诚 E-mail:qbsong@zjut.edu.cn;czhang@zjut.edu.cn
  • 基金资助:
    中国博士后科学基金(2018M632498);浙江省博士后基金(Z71101009);国家自然科学基金(51603185);国家自然科学基金(51673174);浙江省自然科学基金(LY17E030001)

Stabilization of the E/Z Configuration for Cyanostilbene-based Luminogens by Enhanced Charge Transfer Excited State

Yujie DONG,Chendong XU,Shizhao WANG,Weijun LI,Qingbao SONG*(),Cheng ZHANG*()   

  • Received:2018-07-04 Online:2018-10-31 Published:2018-10-31
  • Contact: Qingbao SONG,Cheng ZHANG E-mail:qbsong@zjut.edu.cn;czhang@zjut.edu.cn
  • Supported by:
    The project was supported by the China Postdoctoral Science Foundation(2018M632498);the Zhejiang Provincial Postdoctoral fellowship, China(Z71101009);the National Natural Science Foundation of China(51603185);the National Natural Science Foundation of China(51673174);the Zhejiang Provincial Natural Science Foundation, China(LY17E030001)

摘要:

在前期工作中,我们报道了一个三苯胺基团键接氰基二苯基乙烯单元的分子TPNCF,并认为从局域激发态到电荷转移(CT)激发态的快速内转换,能够有效抑制E/Z异构化反应。为了进一步证明CT态能够诱导E/Z构型的稳定,本文中我们将三苯胺基团替代为给电子能力更强的吩噁嗪基团,设计合成了分子PZNCF,并且成功获得其E/Z异构体。通过对原位核磁及紫外光谱数据的分析,我们发现相比于TPNCF,PZNCF在光辐照下的E/Z异构化反应明显变慢。这说明对于氰基二苯基乙烯单元,一个更强给电子能力基团吩噁嗪的引入能够使其在激发态下具有更稳定的E/Z构型。密度泛函理论计算及光物理测试结果表明PZNCF分子具有较强的电荷转移激发态,这也更加证实了我们先前的结论:通过合理构建给受体结构,能够获得激发态下构型稳定的E/Z异构体。

关键词: E/Z构型, 电荷转移激发态, 氰基二苯基乙烯, 给受体结构, 局域激发态

Abstract:

The E/Z isomerization reaction is found extensively in most organic molecules containing double bond unit. This limits their practical application as luminescent materials partly, especially under photoirradiation. Therefore, it is important to obtain E/Z isomers with stable configuration in the excited state after photoirradiation. It is well known that cyanostilbene and its analogues play an important role in the development of organic opto/electronic materials. The substituted cyano group on C=C double bonds has strong electron-withdrawing ability and large steric hindrance, which benefits the formation of donor-acceptor (D-A) structures and formation of intramolecular charge transfer. In our previous work, we reported a triphenylamine-cyanostilbene molecule (TPNCF) formed by modifying the cyanostilbene structure with triphenylamine, which maintained a stable E/Z configuration as a film and in high polar solvents. According to solvatochromism mechanisms and the results of theoretical calculations, we proposed that the charge transfer (CT) excited state between the triphenylamine donor and cyanostilbene acceptor groups induced the stable configuration of the E- and Z- isomers under photoirradiation. Under irradiation, the E/Z isomerization process occurring at a higher energy locally excited (LE) state was suppressed by a rapid internal conversion process from the LE to CT state. This work inspired us to provide a universal and effective molecular design strategy by modifying D-A substituents on double bonds that can successfully stabilize E/Z isomers. To further confirm that the CT excited state induced stable E- and Z- isomers in the cyanostilbene structure under photoirradiation, we designed and synthesized a donor-acceptor phenoxazine-cyanostilbene molecule (PZNCF) and successfully characterized its two E/Z isomers. In comparison with the reported TPNCF molecule, the in-situ NMR and UV spectra of E- and Z- isomers of PZNCF demonstrated that the E/Z isomerization rate became slower under photoirradiation, which indicated that the stronger electron-donating group of phenoxazine substituted in the cyanostilbene structure induced a more stable E/Z isomer configuration in its excited state. DFT calculations and photophysical results indicated that a stronger CT state was generated in both E- and Z- isomers of PZNCF. This further confirmed our hypothesized mechanism where the stable E/Z configuration can be obtained under photoirradiation by forming a suitable donor-acceptor structure to suppress the E/Z isomerization reaction in the LE state by a rapid internal crossing process from the LE to CT state. This molecular design strategy is of great significance to organic photochemistry and photoelectronics for molecules with double bond units.

Key words: E/Z configuration, Charge transfer excited state, Cyanostilbene, Donor-acceptor structure, Locally excited state

MSC2000: 

  • O644