Figure 2 (a) Characteristics of the Friedel–Crafts gridizations, structure and nomenclature of products. Green: chiral group. Blue: positioning group. (b) Comparison diagram of product yields of different synthons and thiophene reactions. (c) Ratio diagram of the yield of DGs, TGs and NGs under different reaction precursor conditions.
detected and oligomeric nanogrids (DG7, 32%; TG7, 23%; NG7, 35% and DG8, 38%; TG8, 36%; NG8, 19%) were the main products (Figure 2c). The results were consistent with those of BINDFOH, but the yield of AGs was significantly higher in the gridization of DPDFOH. Moreover, we found that with an increase in chain length, DPDFOH had a better ability to synthesize small-sized nanogrids than BINDFOH. Overall, the reaction is less favorable for the gridization pathway as the dihedral angle of axial chirality increases.
The structures of AGs were demonstrated by MALDI-TOF-MS and NMR spectra. Figure 3a shows the 1H NMR spectra of Mix-BINDFOH, UG1 and AG1. The disappearance of the characteristic peak at 2.41‒2.38 ppm in the 1H NMR spectra of UG1 and AG1, compared to Mix-BINDFOH. Especially, the characteristic peak at 4.94 ppm was not observed in the 1H NMR spectra of UG1 and AG1 (Figure S5). These results suggest that formation of a C‒C bond in the 9-position of fluorene. Meanwhile, in the 1H NMR spectrum of UG1, a doublet at 7.05–7.03 ppm (J = 5.2 Hz) and a triplet at 6.74–6.72 ppm (J = 4.0 Hz) can be assigned to proton α (two hydrogens) and proton β1 (two hydrogens) of thiophene, respectively. However, in the 1H NMR spectrum of AG1, the characteristic peak of proton α disappears and the peak of proton β was observed at 6.18 ppm, changes from triplet peak to single peak, indicating the formation of nanogrid. Finally, to elucidate the precise structures of AGs, single crystals of AG1 and AG6 were grown using the slow evaporation method. Fortunately, single crystal of AG6 was obtained in the mixed solvents of dichloromethane and hexane (Figure S6).AG6 (CCDC: 2183271; space group: P-1) exhibited aC2 -symmetric skeleton with the two waist line length of 1.11 nm and 1.12 nm, and the bottom edge length