Lattice Expansion of Highly Oriented 2D Phthalocyanine Covalent Organic Framework Films
Lattice Expansion of Highly Oriented 2D Phthalocyanine Covalent Organic Framework Films
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DOI：
10.1002/anie.201107070
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Dichtel, William R.
中科院分区：
文献类型：
--
作者：
Spitler, Eric L.;Colson, John W.;Dichtel, William R.
指导有机半导体的长程有序和取向对于提高其性能至关重要。[1]用于本体异质结有机光伏器件 (OPV) 的多组分薄膜面临最大的困难，因为必须以系统的方式控制两种不相容材料的堆积、排列和界面。 [2]在微米长度尺度上操纵分子或聚合物组织的策略结合了化学设计和加工技术的各个方面。值得注意的合成方法包括基于并苯的有机半导体的晶体工程[3]和由附加功能介导的非共价组装，[4]包括盘状液晶，[5]或形状互补性。[6]然而，预测或设计功能性芳香系统的包装仍然极其困难，因为小的化学修饰往往会引起固态结构的重大变化。较长长度范围内的有序和取向通常是在成膜或退火过程中通过基板图案化、[7] 电场或磁场对准、[8] 区域精炼、[9] 或二嵌段共聚物相分离来实现。 [10]共价有机框架 (COF) 是一类新兴材料，能够以可预测的方式组织和排列有机半导体。[11-14]COF 合成使用可逆共价键形成反应将分子构建块连接成周期性二维 (2D) 或三维网络。 2D 变体结晶成包含堆叠芳香族亚基的层状结构，非常适合层间激子和电荷传输。[15-17] 2D COF 表现出几个理想且独特的特征：其连接基团的长度和相对方向决定了晶格结构，这与传统有机半导体不可预测的堆积形成鲜明对比。此外，它们的永久孔隙度为额外的功能化提供了连续的高表面积界面。 COF 通常被分离为不溶且不可加工的粉末，不易融入设备中，但我们最近在单层石墨烯 (SLG) 上合成了定向 COF 薄膜。 [18]这些薄膜非常适合有序异质结，只是它们的孔太小而无法容纳互补半导体的连续域。可行的晶格膨胀是网状化学的一个原则，但在 COF 中基本上没有得到证实。仅报道了与 OPV 最相关的方形酞菁网络的最小可能孔径 (2.3 nm)。 [13]在这里，我们通过使用迄今为止纳入 COF 中的最长连接体，描述了 2D 锌酞菁 (ZnPc) COF，其对角线孔径扩大为 2.7、3.4、4.0 和 4.4 nm（图 1）。我们在相似的反应条件下制备了每种 COF，既作为不溶性粉末又作为 SLG 上的定向薄膜。与我们制备的任何其他薄膜相比，其中一种 ZnPc COF 薄膜表现出优异的结晶度和垂直取向。调整这些材料的孔隙率和组成，同时保持其理想的拓扑结构，证明了 COF 方法的多功能性和功效。通过将八羟基酞菁锌 (5) 与方案 1 中所示的四种不同线性二硼酸连接体中的每一种缩合，将 COF 合成为粉末。COF 合成在密封玻璃安瓿中以 2:1、3:1 或 二恶烷:MeOH 5:1混合物，在1208℃下反应72小时。 COF 可重复分离为不溶性微晶粉末，其 FT-IR 光谱证实了在 1340 cm¿1 附近共振的硼酸酯键的形成，并显示出减弱的羟基拉伸（参见支持信息，图 S8-S17…
Directing the long-range order and orientation of organic semiconductors is critical to improving their performance.[1] Multicomponent films used in bulk heterojunction organic photovoltaic devices (OPVs) present the greatest difficulty, as the packing, alignment, and interfaces of two incompatible materials must be controlled in a systematic manner.[2] Strategies for manipulating molecular or polymer organization over micrometer length scales combine aspects of chemical design and processing techniques. Notable synthetic approaches include crystal engineering of acene-based organic semiconductors [3] and noncovalent assembly mediated by appended functionality,[4] including discotic liquid crystals,[5] or shape complementarity.[6] However, it remains extremely difficult to predict or design the packing of functional aromatic systems, as small chemical modifications often induce major changes in solid-state structure. Order and orientation over longer length scales are typically achieved during film formation or annealing through substrate patterning,[7] electrical or magnetic field alignment,[8] zone refining,[9] or diblock copolymer phase separation.[10] Covalent organic frameworks (COFs) are an emerging class of materials that organize and align organic semiconductors predictably.[11–14] COF syntheses use reversible covalent bond-forming reactions to link molecular building blocks into periodic two-dimensional (2D) or three-dimensional networks. The 2D variants crystallize into layered structures containing stacked aromatic subunits ideal for interlayer exciton and charge transport.[15–17] 2D COFs exhibit several desirable and unique features: The length and relative orientation of their linking groups determine the lattice structure, in contrast to the unpredictable packing of traditional organic semiconductors. Also, their permanent porosity provides a continuous, high surface area interface for additional functionalization. COFs are typically isolated as insoluble and unprocessable powders not easily incorporated into devices, but we recently synthesized oriented COF thin films on single-layer graphene (SLG).[18] These films would be well suited for ordered heterojunctions except their pores are too small to accommodate continuous domains of complementary semiconductors. Feasible lattice expansion is a tenet of reticular chemistry but is largely undemonstrated in COFs. Only the smallest possible pore width (2.3 nm) of the square phthalocyanine network most relevant for OPVs has been reported.[13] Here we describe 2D Zn phthalocyanine (ZnPc) COFs with expanded diagonal pore widths of 2.7, 3.4, 4.0, and 4.4 nm (Figure 1), by using the longest linkers incorporated into COFs thus far. We prepared each COF under similar reaction conditions, both as an insoluble powder and as an oriented film on SLG. One of the ZnPc COF films exhibits superior crystallinity and vertical alignment compared to any other film we have prepared. Tuning the porosity and composition of these materials while maintaining their desirable topology demonstrates the versatility and power of the COF approach.The COFs were synthesized as powders by condensing Zn octahydroxyphthalocyanine (5) with each of the four different linear diboronic acid linkers shown in Scheme 1. The COF syntheses were performed in sealed glass ampoules in 2: 1, 3: 1, or 5: 1 mixtures of dioxane: MeOH at 1208C for 72 h. The COFs were reproducibly isolated as insoluble microcrystalline powders whose FT-IR spectra confirmed the formation of boronate ester linkages resonant near 1340 cm¿ 1 and showed attenuated hydroxy stretches (see Supporting Information, Figures S8–S17 …