Poddar Madhurima, Jang Youngwoo, Misra Rajneesh, D'Souza Francis
Department of Chemistry, Indian Institute of Technology, Indore, 453552, India.
Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, TX, 76203-5017, USA.
Chemistry. 2020 May 26;26(30):6869-6878. doi: 10.1002/chem.202000346. Epub 2020 May 8.
A new set of donor-acceptor (D-A) conjugates capable of undergoing ultrafast electron transfer were synthesized using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-substituted phenothiazine, SM1-SM3, by a Pd-catalyzed Sonogashira cross-coupling reaction and a [2+2] cycloaddition-electrocyclic ring-opening reaction. The incorporation of 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD (abbreviated as DCNQ=dicyanodiquinodimethane) in BODIPY-substituted phenothiazine resulted in significant perturbation of the optical and electronic properties. The absorption spectrum of both SM2 and SM3 showed red shifted absorption as compared to SM1. Additionally, both SM2 and SM3 exhibited a distinct intramolecular charge-transfer (ICT) transition in the near-IR region more so for SM3. The electrochemical study revealed multi-redox processes due to the presence of redox-active phenothiazine, BODIPY, TCBD or DCNQ entities. Using data from spectral, electrochemical and computational studies, an energy-level diagram was established to witness excited-state electron-transfer events. Finally, evidence of electron transfer and their kinetic information was secured from studies involving a femtosecond transient absorption technique. The time constants for excited-state electron-transfer events in the case of SM2 and SM3 were less than 5 ps revealing ultrafast processes.
通过钯催化的Sonogashira交叉偶联反应和[2+2]环加成-电环化开环反应，使用4,4-二氟-4-硼-3a,4a-二氮杂-s-茚（BODIPY）取代的吩噻嗪（SM1-SM3）合成了一组能够进行超快电子转移的新型供体-受体（D-A）共轭物。在BODIPY取代的吩噻嗪中引入1,1,4,4-四氰基丁-1,3-二烯（TCBD）和环己-2,5-二烯-1,4-二亚基扩展的TCBD（缩写为DCNQ = 二氰基二喹喔啉二甲烷）导致光学和电子性质发生显著扰动。与SM1相比，SM2和SM3的吸收光谱均显示出红移吸收。此外，SM2和SM3在近红外区域均表现出明显的分子内电荷转移（ICT）跃迁，SM3更为明显。电化学研究表明，由于存在氧化还原活性的吩噻嗪、BODIPY、TCBD或DCNQ实体，会发生多氧化还原过程。利用光谱、电化学和计算研究的数据，建立了能级图以见证激发态电子转移事件。最后，通过涉及飞秒瞬态吸收技术的研究获得了电子转移的证据及其动力学信息。SM2和SM3情况下激发态电子转移事件的时间常数小于5 ps，表明是超快过程。
