Charge Dynamics in A Donor-Acceptor Covalent Organic Framework with Periodically Ordered Bicontinuous Heterojunctions
Charge Dynamics in A Donor-Acceptor Covalent Organic Framework with Periodically Ordered Bicontinuous Heterojunctions
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DOI：
10.1002/anie.201209513
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Jiang, Donglin
中科院分区：
文献类型：
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作者：
Jin, Shangbin;Ding, Xuesong;Jiang, Donglin
施主-受主异质结是当前技术中的关键结构，包括晶体管、发光二极管和光致发光器件，因为它控制器件中的电荷动力学。[1-3]共价有机框架（COF）是结晶分子骨架，其允许结构单元原子精确地整合成周期性阵列结构。[4-12]在这方面，我们已经证明了芳烃，卟啉和酞菁COF，它们提供了π组分的周期性有序柱状阵列，并显示出出色的半导体和光电导性能。[6]我们最近合成了一种供体-受体COF [6 i]，其产生了周期性有序的双连续异质结结构和以纳米级间隔分离的自分选供体和受体柱状阵列。这种纳米级偏析形态形成了电荷分离的宽界面，为电荷收集提供了双极路径，并且对于涉及光能转化的当前半导体器件是理想的;然而，电荷动力学，这是控制能量转化的关键机制，仍然不清楚。在这里，我们报告的供体-受体COF，这是确定使用时间分辨光谱，以阐明从它们的产生离域和保留的自由电荷的光化学过程的电荷动力学。在COF中，异质结允许从供体到受体柱的超快电子转移。因此，光吸收与电荷解离直接耦合，以在2 ps内在供体和受体π-柱中产生自由电荷。另一方面，堆叠的π-柱使电荷离域，抑制电荷复合，并且将电荷保持延长的时间段。我们发现，溶剂化和固态COF，使快速的电荷分离和特殊的长期电荷保持，从而提供了一个关键的机制基础，设想的高潜力的给体-受体COF的光电applications.The给体-受体COF（方案1a，DZnPc-ANDI-COF）是一个四面体，介孔的2D框架，是由酞菁锌作为电子供体和萘二酰亚胺作为受体。在COF中，两个π-单元在电子转移距离内以约428的二面角交替连接。COF提供了自分选的双连续柱状阵列，并构成了周期性结构的异质结，其中每个供体柱与四个受体柱连接，这四个受体柱在捕获光生电子方面具有同等活性（方案1b）。DZnPc-ANDI-COF吸收高达1100 nm的可见光和近红外区域的光（支持信息中的图S1）。元素分析、红外光谱、核磁共振光谱和电子显微镜证实了COF的形成（图S2-S4和表S1）。相同的COF已被报道为薄膜。[8c]
The donor–acceptor heterojunction is a key structure in current technologies, including transistors, light-emitting diodes, and photovoltaics, because it controls the charge dynamics in the devices.[1–3] Covalent organic frameworks (COFs) are crystalline molecular skeletons that allow atomically precise integration of building blocks into periodic array structures.[4–12] In this regard, we have demonstrated arene, porphyrin, and phthalocyanine COFs that provide periodically ordered columnar arrays of π-components and show outstanding semiconducting and photoconductive properties.[6] We recently synthesized a donor–acceptor COF [6i] that gives rise to a periodically ordered bicontinuous heterojunction structure and self-sorted donor and acceptor columnar arrays separated at nanometer-scale intervals. This nanoscopic segregation morphology forms a broad interface for charge separation, provides ambipolar pathways for charge collection, and would be ideal for the current semiconducting devices that involve photoenergy transformations; however, the charge dynamics, which is a key mechanism that controls the energy transformation, remains unclear. Here, we report the charge dynamics of a donor–acceptor COF, which were determined using time-resolved spectroscopy to elucidate the photochemical processes of the free charges from their generation to delocalization and retention. In the COF, the heterojunctions allow an ultrafast electron transfer from the donor to the acceptor columns. Consequently, the light absorption is directly coupled with charge dissociation to generate free charges in the donor and acceptor π-columns within 2ps. On the other hand, the stacked π-columns delocalize the charges, suppress charge recombination, and retain the charges for a prolonged period of time. We show that both solvated and solid-state COFs enable rapid charge separation and exceptional long-term charge retention, thereby providing a key mechanistic basis to envisage the high potential of donor–acceptor COFs for photoelectric applications.The donor–acceptor COF (Scheme 1a, DZnPc-ANDI-COF) is a tetragonal, mesoporous 2D framework that is composed of zinc phthalocyanine as an electron donor and naphthalene diimide as an acceptor. In the COF, the two π-units are alternately linked within an electron-transfer distance and at a dihedral angle of approximately 428. The COF provides selfsorted, bicontinuous columnar arrays and constitutes periodically structured heterojunctions in which each donor column is interfaced with four acceptor columns that are equally active in capturing photo-generated electrons (Scheme 1b). The DZnPc-ANDI-COF absorbs light over a broad visible and near-infrared region up to 1100 nm (Figure S1 in the Supporting Information). Elemental analysis, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron microscopy confirmed the formation of the COF (Figure S2–S4 and Table S1). The same COF has been reported as a thin film.[8c]