A supramolecular bundling approach toward the alignment of conjugated polymers
A supramolecular bundling approach toward the alignment of conjugated polymers
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DOI：
10.1002/anie.200503128
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Shinkai, S
中科院分区：
文献类型：
--
作者：
Kubo, Y;Kitada, Y;Shinkai, S
Exploring new methods for controlling the orientation and electronic state of π-conjugated oligomers and polymers is of importance for the production of materials with optimized properties and for their ultimate assembly into molecular circuitry. In addition to supramolecular assembly schemes,[1–4] methods for aligning conjugated polymers, which lead to many new photophysical functions, include the use of metastable states enforced by liquid-crystalline phases,[5–7] Langmuir monolayers at the air–water interface,[8] incorporation into prealigned host matrixes,[9, 10] and rubbing.[11, 12] Unlike synthetic macromolecular systems, the bundling proteins found in animal cells bind one-dimensional (1D) actin filaments in high affinity to elicit the formation of actin bundles.[13] The bundling proteins possess two interactive modules for cross-linking actin filaments; their distinct properties determine the type of assembly. If one can reconstruct such modules interacting with 1D materials in a supramolecular manner, not only would these systems provide a new means of aligning the materials but also would create complex mesoscopic structures and networks akin to those found in nature. Herein, we report a new concept for aligning and assembling conjugated polymers through the action of supramolecular bundling (“aligner”) molecules. We demonstrate this concept by utilizing the dative bonds formed between porphyrinatozinc and amine derivatives because of the high affinity and distinct bonding geometry of these species.[14] We designed the aligner molecules 1 and 2, which are porphyrinatozinc oligomers,[14, 15] to elicit positive homotropic allosterism [16–18] during their binding of the amino-functionalized conjugated polymers CP and CCP in an effort to organize the polymers into aligned, rather than random, assemblies (Figure1). Although the distances between pairs of porphyrinatozinc units in 1 and 2 aligned in parallel can vary through conformational rearrangements about their rotational axes (the butadiyne unit for 1 and the ethylene bridges for 2), the distances between the binding subunits when in a cofacial orientation are 2.5 and 2.0 nm, respectively. Each pair of cofacially aligned porphyrinatozinc tweezers in 1 and 2 binds to a diamine moiety of the polymer in an allosteric manner to form polymer bundles (Figure 1 B); in this process, the binding of the first polymer to an aligner molecule facilitates the second binding, which results in the ready formation of aligned assemblies (Figure 1 C).To confirm the cooperativity of the binding of CP and CCP by 1 and 2, we used MCP as a guest molecule for 1 and 2. We noted the formation of the [1· MCP] or [2· MCP] complexes in CHCl3 from changes in the UV/Vis absorption spectra that occurred upon the successive addition of MCP (see the Supporting Information). The values of λmax of the Soret and Q bands shifted to longer wavelengths with tight isosbestic points; these changes are consistent with those observed from studies of other porphyrinatozinc–amine coordination systems.[14] We estimated the stoichiometries of the complexes formed between MCP and both 1 or 2 from molar ratio plots, which clearly indicated the formation of 1: 2 [1·(MCP) 2] and 1: 3 [2·(MCP) 3] complexes. Importantly, plots of absorbance at the Q band (607 nm) versus [MCP] possessed sigmoidal curvature. From analyses of these binding isotherm using nonlinear-curve-fitting and Hill-plot [19] methods, we calculated the association constants (Kn/MCP) and Hill coefficients (nH) to be K1= 1.6 105, K2= 3.0 105, and nH= 1.9 for [1·(MCP) 2] and K1= 8.8 105, K2= 9.2 105, K3= 4.8 106, and nH= 2.8 for [2·(MCP) 3]. These results …
