The Ugi Four-Component Reaction Route to Photoinducible Electron-Transfer Systems
The Ugi Four-Component Reaction Route to Photoinducible Electron-Transfer Systems
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DOI：
10.1002/cplu.201200279
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发表时间：
2013-02-01
期刊：
影响因子：
3.4
通讯作者：
Mueller, Thomas J. J.
中科院分区：
文献类型：
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作者：
Bay, Sarah;Villnow, Torben;Mueller, Thomas J. J.
在功能有机材料中，[1] 供体-受体 (D-A) 缀合物引起了人们对分子电子学和光电子学等先进和未来技术的极大兴趣。它们构成了整流器、非线性光学材料[2]和光伏器件[3]的关键功能单元。特别是，光到电流的转换是建立在光致电子转移（PET）原理的基础上的。[4]除了完善的供电子部分，例如卟啉、多环芳烃、苝二酰亚胺[5]和（低聚）噻吩[6]，吩噻嗪（PT）衍生物[3b，7]由于其可逆和可调的氧化电位，作为电泳剂变得越来越有吸引力。另一方面，富勒烯[8]和9, 10-蒽醌（AQ）衍生物[9]已在D-A系统中作为有利的电子受体单元得到应用。例如，PT-受体二联体显示分子内 PET，可以通过 PT 荧光的猝灭轻松识别。 [10]电荷分离态的形成可以通过各种光谱方法来验证，例如 EPR 光谱、闪光光解或超快瞬态光谱。尽管吩噻嗪和蒽醌的组合作为基于肽支架[11]和刚性炔基桥联[12]的有利D-A对已经在PET方面被提出、制备和研究，但迄今为止，尚未探索一种通用、简便且面向多样性的D-A系统合成方法。令人惊讶的是，在这项工作之前，从未探索过通过多组分反应来合成这些类型的功能性 π 电子系统的最优雅的方法。特别是Ugi四组分反应（4CR）[13]，它提供了具有高水平多样性的化学稳健的α-氨基酰酰胺支架，广泛应用于生物和药物化学[14]，但之前从未用于合成功能性D-A PET系统。在此，我们报告了基于 PT-AQ 的 PET 系统的第一个 Ugi 4CR 路线，并通过循环伏安法、稳态紫外/可见光和荧光光谱以及飞秒瞬态吸收光谱进行电子表征，以识别光激发后所需的电荷分离状态。在使用吩噻嗪基甲基氯化铵（通过用氢氧化钾释放碱）进行 Ugi 4CR 时，[15]在室温下，将蒽醌-2-甲醛、乙酸和叔丁基异氰化物在甲醇和二氯甲烷中，以良好的产率获得 PT-AQ 双联体 1（方案 1）。同样，为了进行光谱比较，Ugi 4CR 也成功应用于合成仅受体参考 3，使异丙胺作为氨基组分，仅供体 2 与乙醛反应（方案 1）。
Among functional organic materials,[1] donor–acceptor (D–A) conjugates have aroused preeminent interest in advanced and future technologies, such as molecular electronics and optoelectronics. They constitute key functional units in rectifiers, nonlinear optical materials,[2] and photovoltaic devices.[3] In particular, light-to-current conversion is founded on the principles of photoinduced electron transfer (PET).[4] Besides well-established electron-donating moieties, such as porphyrins, polycyclic aromatic hydrocarbons, perylenediimides,[5] and (oligo)-thiophenes,[6] phenothiazine (PT) derivatives [3b, 7] have become increasingly attractive as electrophores because of their reversible and tunable oxidation potentials. On the other hand, fullerene [8] and 9, 10-anthraquinone (AQ) derivatives [9] have found application as favorable electron-acceptor units in D–A systems. For instance, PT–acceptor dyads display intramolecular PET, which can be identified readily by quenching of the PT fluorescence.[10] The formation of charge-separated states can be verified by various spectroscopic methods, such as EPR spectroscopy, flash photolysis, or ultrafast transient spectroscopy. Although combinations of phenothiazines and anthraquinones as advantageous D–A pairs based upon peptide scaffolds [11] and rigid alkynyl-bridged dyads [12] have been proposed, prepared, and studied with respect to PET, a general, facile, and diversity-oriented synthetic approach to D–A systems has remained unexplored so far. Surprisingly, the most elegant synthetic approach to these types of functional π-electron systems by multicomponent reactions has never been scouted prior to this work. In particular, the Ugi four-component reaction (4CR),[13] which furnishes the chemically robust α-aminoacyl amide scaffold with high level of diversity, is applied widely in biological and medicinal chemistry [14] but has never been used for the synthesis of functional D–A PET systems before. Herein, we report the first Ugi 4CR route to a PT–AQ-based PET system and its electronic characterization by cyclic voltammetry, steady-state UV/Vis and fluorescence spectroscopy, as well as femtosecond transient absorption spectroscopy for identification of the desired charge-separated state after light excitation.Upon performing the Ugi 4CR with phenothiazinyl methyl ammonium chloride (by liberating the base with potassium hydroxide),[15] anthraquinone-2-carbaldehyde, acetic acid, and tert-butyl isocyanide in methanol and dichloromethane at room temperature, the PT–AQ dyad 1 is obtained in good yield (Scheme 1). Likewise and for spectroscopic comparison, the Ugi 4CR is also successfully applied to synthesize the acceptor-only reference 3 upon reacting isopropylamine as amino component and the donor-only 2 with acetaldehyde (Scheme 1).