Controlled Molecular Orders in Layered Multiple Porphyrins

Abstract

Nature precisely regulates multicomponent assemblies with the assistance of cooperativity. However, establishing such high precision in multicomponent assemblies of artificial supramolecular structures remains challenging. Here, we successfully position multiple distinct guest molecules within two equivalent binding cavities of a zinc-metalated trisporphyrin host by combining two distinct negative cooperative interactions, including donor-acceptor π-stacking and metal-ligand coordination. Comprehensive characterization using UV-vis absorption spectroscopy and diffusion-ordered NMR spectroscopy confirmed the exclusive formation of a ternary supramolecular complex. X-ray crystallographic analysis further revealed that the introduction of an additional bridging ligand effectively linked the two ternary complexes to produce an unprecedented septenary supramolecular assembly with alternating guest sequences. In contrast to conventional methods, which require structural differentiation or positive cooperativity, our strategy relies exclusively on negative cooperativity to achieve highly precise molecular ordering. This study presents a novel approach toward constructing sophisticated multicomponent molecular assemblies, emphasizing the significant but underutilized role of negative cooperativity in achieving molecular precision in artificial supramolecular chemistry.

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Structures of trisporphyrin 1 and 1Zn and guest molecules G1, G2, and G3.

1. Multistep Host–Guest Complexation of 1Zn with G1, G2, and G3

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UV–vis absorption spectra of 1Zn (8.1 × 10^–7 mol L^–1) with (a) G1 (a–j: 0.0, 3.1, 6.5, 10, 16, 24, 40, 65, 120, and 400 × 10^–7 mol L^–1) and (c) G2 (a–h: 0.0, 1.6, 3.3, 4.9, 6.5, 8.1, 16, and 24 × 10^–7 mol L^–1) at 295 K in chloroform. Job plot 1Zn with (b) G1 and (d) G2 at 295 K in chloroform. The total concentration of a mixture of host and guest was maintained at a constant value (1Zn + G1: 2.0 × 10^–4 mol L^–1; 1Zn + G2: 2.0 × 10^–4 mol L^–1). ΔAbs′ indicates |Abs – Abs_H·X – Abs_G·X|, where Abs, Abs_H, and Abs_G indicate the observed absorbance, absorbance of the host, and absorbance of the guest, respectively.

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(a, b) UV–vis absorption spectral changes of 1Zn (2.0 × 10^–5 mol L^–1) upon addition of G1 (a–i: 0.0, 0.38, 0.77, 1.2, 1.6, 2.1, 2.8, 8.1, and 30 × 10^–5 mol L^–1) and then G2 (i–q: 0.0, 0.42, 0.83, 1.2, 1.7, 2.1, 2.8, 5.3, and 30 × 10^–5 mol L^–1) at 295 K in chloroform. (c, d) UV–vis absorption spectral changes of 1Zn (2.0 × 10^–5 mol L^–1) upon addition of G2 (a–i: 0.0, 0.42, 0.83, 1.2, 1.7, 2.8, 3.8, 6.1, and 30 × 10^–5 mol L^–1) and then G1 (i–q: 0.0, 0.38, 0.77, 1.2, 1.6, 2.1, 2.8, 5.3, and 30 × 10^–5 mol L^–1) at 295 K in chloroform. (e) Plots of Abs at 563 nm of 1Zn versus ([G1] + [G2])/[1Zn] upon the stepwise addition of G1 (circle) and G2 (rhombus).

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¹H NMR spectra of (a) G1, (b) G2, and (c) a 1:1:1 mixture of 1Zn, G1, and G2. (d) Diffusion coefficients of a 1:1:1 mixture of 1Zn, G1, and G2 (blue line) and a 1:1:1.5 mixture of 1Zn, G1, and G2 (red line).

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Crystal structures of G2•1Zn•G1•G2•G1•1Zn•G2 from (a) the side and (b) the top. Guest molecules G1 and G2 are shown in red and blue, respectively. All hydrogen atoms have been omitted for clarity.

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¹H NMR spectra of (a) a 1:1:1:0.5 mixture of 1Zn, G1, G2, and G3, and (b) diffusion coefficients of a 1:1:1 mixture of 1Zn, G1, and G2 (blue line) and a 1:1:1:0.5 mixture of 1Zn, G1, G2, and G3 (red line).