Predicting the Switchable Screw Sense in Fluorene‐Based Polymers

Abstract

A chirality‐switching free‐energy landscape was reconstructed on a 43‐mer of poly(9,9‐dioctylfluoren‐2,7‐diyl) (PDOF). The simulations were conducted on amorphous silica surface as well as in the vacuum phase for a single chain or for a group of sixteen chains. The achiral‐to‐chiral transition occurs only on amorphous silica (activation free‐energy 35 kcal mol−1), where the enantiomeric (homochiral) basins are detected. This was supported by the experiments where effective chirality induction to PDOF using circularly polarized light (CPL) was attained only for a film deposited on a quartz glass and not for a solution or a suspension. These results indicate that interactions of PDOF with amorphous silica play a crucial role in chirality switching. Importance of chain assembling was also indicated. Theoretical ECD spectra of the enantiomeric basins containing a 51 helix reproduce the experimental spectra.

Chirality analysis of helical polymers

“…Pietropaolo & Nakano, 2013, 2020Pietropaolo, Cozza, Zhang, & Nakano, 2018;Sakamoto, Fukuda, Sato, & Nakano, 2009). In the case of poly(9,9-dioctylfluroene-2,7-diyl) discussed earlier, the presence and the absolute helical sense of the helix were concluded by the following: (1) the most probable conformation was estimated, (2) theoretical CD spectra were calculated for the conformation, and (3) matching of the theoretical CD spectra with experimental CD spectra was confirmed ( Figure 6) (Pietropaolo et al, 2015). The combination of experiments and theoretical calculations is thus a powerful method of chirality analysis of the helix.…”

“…While any conformation having no planes of symmetry can account for chiroptical properties, a helix may be proposed as the simplest one. As a typical example of a helical polymer having no centers or planes of chirality, optically active poly(9,9-dioctylfluorene-2,7-diyl) has been reported ( Figure 3A) (Pietropaolo, Wang, & Nakano, 2015;Wang, Sakamoto, & Nakano, 2012;Wang, Harada, Phuong, Kanemitsu, & Nakano, 2018). Because axial chirality around the single bond's connecting monomeric units is the only chiral element for this polymer, a preferred-handed twist is reasonably proposed to explain its chiroptical properties, and accumulated twists of the same hand in a chain means a preferred-handed helix.…”

Effect of Different Z‐Inducers on the Stabilization of Z Portion in BZ‐DNA Sequence: Correlation Between Experimental and Simulation Data

“…The free energy profile of the B‐Z junction and its brominated variant at position 8 of G2’ and G4’ (Fig. ) was reconstructed along a chiral descriptor represented by the z G coordinate . The z G coordinate indicates how far a given conformation sampled during the simulation is from the X‐ray structure of the B‐Z junction( pdb code 2ACJ ).…”

Helical screw sense bias in chiral polyfluorene stimulated by solvent

“…Chemists have successfully realized the helical chirality switching by means of external stimuli, such as solvent, temperature, light irradiation, pH and so on. [21][22][23][24][25][26][27][28][29][30][31] In particular, intrinsic chirality exists in many organic solvents (e.g., limonene), and it tends to influence the solute conformation, then results in complete helical chirality inversion. Gin and Moore demonstrated that [This article is part of the Special Issue: Proceedings of 28th International Symposium on Molecular Chirality, Heidelberg 2016.…”

“…Interestingly, supramolecular helical handedness of chiral materials is not invariable, actually, they display conformational transformations under certain treatments. Chemists have successfully realized the helical chirality switching by means of external stimuli, such as solvent, temperature, light irradiation, pH and so on . In particular, intrinsic chirality exists in many organic solvents (e.g., limonene), and it tends to influence the solute conformation, then results in complete helical chirality inversion.…”