Figure 1 The conceptual scheme of A-type and molecular A-type
nanogrids (AGs) structures as a model of the nanolinkage.
synthesizing AGs, yielding 9–30%. Additionally, we observed that the
yield of AGs obtained with R /S -BINDFOH was significantly
higher than that obtained with Mix-BINDFOH. Meanwhile, theoretical
calculations and experimental results demonstrate that a smaller
dihedral angle of the axial chiral group improves the yield of AGs.
Finally, the nanogrid effect of AGs is confirmed by OFET memory devices.
Before synthesizing AGs, their structures were optimized and calculated
density functional theory (DFT) at the B3LYP/6-31+G(d) level of theory.
The structure of AGs (AG1 as an example) has six stable stereoisomers
that can be divided into two pairs ofC2 -symmetric rac -isomers (aRSS -AG1,
and aSRR -AG1; aRRR -AG1 and aSSS -AG1) and two
asymmetric meso -configurations (aRSR -AG1 andaSRS -AG1) (Figure S1). Moreover, using the energy ofaRSS -AG1 and aSRR -AG1 (0 kcal/mol) as reference, the total
energies of the other four stereoisomers are 5.968 kcal/mol
(aRSR -AG1), 5.968 kcal/mol (aSRS -AG1), 14.411 kcal/mol
(aRRR -AG1), and 14.411 kcal/mol (aSSS -AG1), respectively
(Figure S2). These results suggest that achieving stereoselective
synthesis of AGs could be challenging because the total energies of each
stereoisomer are relatively similar. Meanwhile, to investigate the
effect of the chain length of B2 synthons on the properties of AGs, we
calculate the strain energies and dihedral angle (on axial chirality) of
AG1 (11.533 kcal/mol and 83o), AG4 (32.854 kcal/mol
and 91o) and AG5 (40.728 kcal/mol and
107o) (Figure S3, Table S1). These results shown that
as the chain length of B2 synthons increases, the strain energies and
dihedral angle of AGs also increases gradually.
Results and Discussion
To optimize the reaction conditions, we employed 1,1′-binaphthyl
difluorenols (Mix-BINDFOH, A2) and thiophene as model reactions under
different Brønsted or Lewis acid mediators, solvent, time and acids
concentration conditions (Table S2).
BF3·Et2O exhibited the best performance,
providing a yield of 9% for AG1. Meanwhile, during such process,
byproducts such as UG1, dimer gridization product DG1, trimer
gridization product TG1, and oligomeric gridization product NG1
(N>3) (N represents the number of duplicate units) were
obtained in 9%, 51%, 12% and 16%, respectively.
Next, to further investigate the effect of the chirality of
binaphthalene on the yields of nanogrids, we examined (R )-BINDFOH
and (S )-BINDFOH under the optimized conditions. Surprisingly, the
yields of AG2 (16%) and AG3 (20%) significantly increased compared to
Mix-BINDFOH when R /S -BINDFOH was used as the substrate.
Moreover, the yield of DG2 (38%), DG3 (43%), and ungridization UGs
(trace) decreased accordingly (Figures 2a and 2b). The results suggest
that both Mix-BINDFOH and R /S -BINDFOH support a
gridization pathway rather than a linear polymerization pathway, with
their primary product being DGs, probably due to the smaller strain
energies of DGs than AGs. Notably, the proportion of AGs produced byR /S -BINDFOH was significantly higher than that of
Mix-BINDFOH, which may be due to more competitive reactions. Thirdly, to
study the effect of the dihedral angle of axial chirality on the
gridization reaction, we explored different sizes of B2 synthons. We
tested this protocol using bithiophene (BTh) and terthiophene (TTh),
which have longer molecular chains than thiophene but the same reactive
site. As a result, the expect AGs (AG4 and AG5) were not observed, due
to the larger dihedral angle of AG4 and AG5 compared to AG1. Instead,
oligomeric nanogrids DGs (DG4, 30%; DG5, 22%), TGs (TG4, 23%; TG5,
30%) and NGs (NG4, 37%; NG5, 40%) were obtained (Figure 2c). These
results indicated that i) as the dihedral angle of the axial chirality
increases, the reaction does not support the formation of AGs and ii) as
the chain length of B2 synthons increases, the reaction tends to
generate oligomeric nanogrids with large molecular weight. Finally, to
verify the above results, we further examined biphenyl difluorenols
(DPDFOH, mixed stereoisomers) under the optimized conditions. Similarly,
we found that when thiophene was used as B2 synthon, AG6 (dihedral
angle, 79o, Table S1) could be obtained in 28% yield
and oli-gomeric nanogrids (DG6, 16%; TG6, 5%) were found. However,
with bithiophene and terthiophene, AG7 (dihedral angle,
109o, Table S1) and AG8 (dihedral angle,
162o, Table S1) were not