Department of Chemistry and Pharmacy & Interdisciplinary Center of Molecular Materials (ICMM), Friedrich-Alexander-University Erlangen-Nuremberg , Egerlandstr. 3, 91058 Erlangen, Germany.
Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid , Ciudad Universitaria s/n, 28040 Madrid, Spain.
J Am Chem Soc. 2017 Dec 6;139(48):17474-17483. doi: 10.1021/jacs.7b08670. Epub 2017 Nov 17.
We report the synthesis of a full-fledged family of covalent electron donor-acceptor-acceptor conjugates and their charge-transfer characterization by means of advanced photophysical assays. By virtue of variable excited state energies and electron donor strengths, either Zn(II)Porphyrins or Zn(II)Phthalocyanines were linked to different electron-transport chains featuring pairs of electron accepting fullerenes, that is, C and C. In this way, a fine-tuned redox gradient is established to power a unidirectional, long-range charge transport from the excited-state electron donor via a transient C toward C. This strategy helps minimize energy losses in the reductive, short-range charge shift from C to C. At the forefront of our investigations are excited-state dynamics deduced from femtosecond transient absorption spectroscopic measurements and subsequent computational deconvolution of the transient absorption spectra. These provide evidence for cascades of short-range charge-transfer processes, including reductive charge shift reactions between the two electron-accepting fullerenes, and for kinetics that are influenced by the nature and length of the respective spacer. Of key importance is the postulate of a mediating state in the charge-shift reaction at weak electronic couplings. Our results point to an intimate relationship between triplet-triplet energy transfer and charge transfer.
我们报告了一系列全功能的共价电子给体-受体-受体共轭物的合成，并通过先进的光物理测定方法对其电荷转移特性进行了表征。通过可变的激发态能量和电子给体强度，锌(II)卟啉或锌(II)酞菁可以与不同的电子传输链相连，这些电子传输链具有一对电子受体富勒烯，即 C 和 C。这样，就建立了一个精细调节的氧化还原梯度，以支持从激发态电子给体通过瞬态 C 向 C 的单向长程电荷传输。这种策略有助于最小化从 C 到 C 的还原、短程电荷转移过程中的能量损失。我们研究的前沿是从飞秒瞬态吸收光谱测量中推断出的激发态动力学，以及瞬态吸收光谱的后续计算反卷积。这些提供了短程电荷转移过程级联的证据，包括两个电子受体富勒烯之间的还原电荷转移反应，以及动力学受到各自间隔物的性质和长度的影响。至关重要的是，在弱电子耦合的电荷转移反应中存在中介态的假设。我们的结果表明三重态-三重态能量转移和电荷转移之间存在密切关系。
