Octapodal Corannulene Porphyrin-Based Assemblies: Allosteric Behavior in Fullerene Hosting

Abstract

An octapodal corannulene-based supramolecular system has been prepared by introducing eight corannulene moieties in a porphyrin scaffold. Despite the potential of this double picket fence porphyrin for doubletweezer behavior, NMR titrations show exclusive formation of 1:1 adducts. The system exhibits very strong affinity for C 60 and C 70 (K 1 = (2.71 ± 0.08) × 10 4 and (2.13 ± 0.1) × 10 5 M −1 , respectively), presenting selectivity for the latter. Density functional theory (DFT) calculations indicate that, in addition to the four corannulene units, the relatively flexible porphyrin tether actively participates in the recognition process, resulting in a strong synergistic effect. This leads to a very strong interaction with C 60 , which in turn also induces a large structural change on the other face (second potential binding site), leading to a negative allosteric effect. We also introduced Zn 2+ in the porphyrin core in an attempt to modulate its flexibility. The resulting metalloporphyrin also displayed single-tweezer behavior, albeit with slightly smaller binding constants for C 60 and C 70 , suggesting that the effect of the coordination of fullerene to one face of our supramolecular platform was still transmitted to the other face, leading to the deactivation of the second potential binding site.

Interacciones supramoleculares de porfirinas funcionalizadas con múltiples sustituyentes poliaromáticos planos y no planos con fullerenos

“…This is in contrast to 2H-Octa(II), in which the corannulene units could establish intramolecular interactions that had to be overcome prior to the inclusion of C60 and that were possible due to the bending of the porphyrin core, revealing its relatively flexible nature. 17 In the case of 2H-PTetraCor, the two corannulene moieties on each side of the porphyrin are preorganized for C60 interaction and adopt an approximately concave-concave conformation with two potential binding sites, as shown in Figure 2. The cleft formed by the two corannulene units is large enough (ca.…”

“…8.73 ± 0.05 × 10 1 for 2H-PTetraCor vs 5.4 ± 0.2 × 10 3 (averaged value from atropisomers) for 2H-tetra(I) and 2.71 ± 0.08 × 10 4 for 2H-Octa(II)). 15,17 The relative difference is even greater for the association of C70 (cf. 5.24 ± 0.02 × 10 1 for 2H-PTetraCor vs 2.13 ± 0.10 × 10 5 for 2H-Octa(II)).…”

“…Corannulene, 1-pinacol corannuleneboronate (Cor-Bpin) and 1-pinacol pyreneboronate (Pyr-Bpin) were obtained following literature procedures. [16][17]25 2H-PTetraBr: Pyrrole (278 μL, 4 mmol), p-bromobenzaldehyde (740 mg, 4 mmol), propionic acid (13 mL, 173 mmol), and nitrobenzene (7 mL, 68 mmol) were mixed in a sealed vessel specifically designed for microwave irradiation. The mixture was stirred inside a microwave reactor at 200 °C for 15 min.…”

“…Además de los más conocidos por el público en general, diamante y grafito, existen otra variedad que en las últimas tres décadas ha revolucionado la ciencia a nivel nanométrico por sus excelentes propiedades fotovoltaicas, mecánicas, ópticas y detectoras, 15 son los conocidos como nanoalótropos de carbono. 16 Estos nanomateriales de carbono pueden clasificarse en función del número de dimensiones que presentan, siendo cero dimensionales (0D) los fullerenos, 17 en donde las tres dimensiones se encuentran a escala nanométrica, monodimensionales (1D) los nanotubos de carbono (CNT) 18 y bidimensionales (2D) el grafeno, 19 donde una y dos dimensión se ubican a escala nanométrica, respectivamente (Figura 1). Todos ellos comparten una hibridación sp 2 en el átomo de carbono, pero la estructura final es muy diferente en función de cómo están organizados a nivel atómico, como puede observarse en la Figura 1.…”

“…15 However, the formation of four inseparable atropoisomers diminished the binding ability of the system and resulted in a difficult to analyse system. Nonetheless, this study highlighted the importance of the participation of the porphyrin core in the recognition process In order to prevent the formation of atropisomers, we first introduced eight pyrene units (i.e., in all meta positions), 16 and, very recently eight corannulene units, 17 at the meta positions of the tetraaryl porphyrin. Figure 1b shows the resulting octapodal corannulene-based system, which features two binding sites as a result of the 4+4 arrangement of the corannulene arms.…”