Stimuli‐Directed Dynamic Reconfiguration in Self‐Organized Helical Superstructures Enabled by Chemical Kinetics of Chiral Molecular Motors

Abstract Dynamic controllability of self‐organized helical superstructures in spatial dimensions is a key step to promote bottom‐up artificial nanoarchitectures and functional devices for diverse applications in a variety of areas. Here, a light‐driven chiral overcrowded alkene molecular motor with rod‐like substituent is designed and synthesized, and its thermal isomerization reaction exhibits an increasing structural entropy effect on chemical kinetic analysis in anisotropic achiral liquid crystal host than that in isotropic organic liquid. Interestingly, the stimuli‐directed angular orientation motion of helical axes in the self‐organized helical superstructures doped with the chiral motors enables the dynamic reconfiguration between the planar (thermostationary) and focal conic (photostationary) states. The reversible micromorphology deformation processes are compatible with the free energy fluctuation of self‐organized helical superstructures and the chemical kinetics of chiral motors under different conditions. Furthermore, stimuli‐directed reversible nonmechanical beam steering is achieved in dynamic hidden periodic photopatterns with reconfigurable attributes prerecorded with a corresponding photomask and photoinduced polymerization.


Experimental details
All starting chemicals, solvents and reagents were purchased from Sigma-Aldrich, TCI or J&K. Analytical thin-layer chromatography (TLC) was performed with aluminum sheets coated on Merck silica gel 60 F254. Column chromatography was carried out on silica gel (200-300 mesh). 1 H and 13 C spectra were recorded on a Bruker 400 MHz spectrometer.

2-methyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-one (M4a)
To polyphosphoric acids (250 ml) at 80 o C was added naphthalene (3.20 g, 25.0 mmol). The mixture was heated to 110 o C under mechanical stirrer, after which methacrylic acid (3.23 g, 37.5 mmol) was added and stirred for 4 h. After cool to 70 o C, the mixture was poured into ice water and stirred for an additional 3 h. The mixture was extracted with CH 2 Cl 2 (3 x 50 mL).
The organic extracts were washed with NaHCO 3 (saturated aqueous solution, 50mL), brine and water and dried on MgSO 4 . The solvent was removed in vacuo and the crude residue was purified by column chromatography (SiO 2 , pentane: CH 2 Cl 2 = 3:1) to yield M4a as light yellow liquid (2.10 g, 41%) 1

2-isopropyl-2,3-dihydro-1H-cyclopenta[a]naphthalen-1-one (M4b)
To polyphosphoric acids (250 ml) at 80 o C was added naphthalene (3.20 g, 25.0 mmol). The mixture was heated to 110 o C under mechanical stirrer, after which 2-isopropylacrylic acid (4.28 g, 37.5 mmol) was added and stirred for 4 h. After cool to 70 o C, the mixture was poured into ice water and stirred for an additional 3 h. The mixture was extracted with CH 2 Cl 2 (3 x 50 mL). The organic extracts were washed with NaHCO 3 (saturated aqueous solution, 50mL), brine and water and dried on MgSO 4 . The solvent was removed in vacuo and the crude residue was purified by column chromatography (SiO 2 , pentane: CH 2 Cl 2 = 5:1) to yield

Kinetic analysis of motors M1-M3 in THF
The thermal relaxation rate (k Δ ) of the first-order thermal motion of the motors M1-M3 (40 μM in THF) was obtained by the decrease in absorbance at 450 nm at 20 0 o C, 25 o C, 30 o C and 35 o C, fitting the first-order chemical reaction: where A 0 is the absorbance at the PSS, A∞ is the absorbance at the initial state and A(t) is the absorbance at time t in the thermal inversion. Calculations of half-life (t 1/2 ), Gibbs free energy of activation (Δ ‡ G°), enthalpy of activation (Δ ‡ H°) and entropy of activation (Δ ‡ S°) were performed using the following equations: where h is Plank's constant, k B is Bolzmann constant, T is absolute temperature, R is gas constant. The thermal kinetic parameters are listed in Table S1.

Photo-induced and thermo-induced chiroptical variation of chiral motors M1-M3 in cholesteric liquid crystals (CLCs)
The chiroptical variation of chiral motors M1-M3 was measured by Grandjean-Cano wedge method. 3 The CLC mixture was fabricated by doping 1.0 wt% chiral motors into a commercial nematic liquid-crystal host SLC1717. The resulting mixture was capillary filled into a wedge cell (EHC, KCRK-07, tan θ = 0.0196). The wedge cell with an opening angle θ was made by two parallel-alignment substrates with two spacers in different thickness at each end of the cell ( Figure S4). The parallel arrangement of CLC produces the disclination lines between the CLC layers in which the interlayer spacer is integer multiples of p/2, where p is the pitch of CLCs as shown in Figure S3. The disclination lines can be observed by a transmission-mode POM. Therefore the pitch can be calculated by the equation p = 2L tan θ, where L is the distance between the disclination lines.

Dynamic analysis of chiral motors M1-M3 in CLCs
The  (2) and (3). The thermal kinetic parameters are listed in Table S1.         To fabricate the diffraction grating CLCs, the motor-doped CLCs containing C6M (20.0 wt%) and Irgacure 784 (1.0 wt%), as listed in Table S2, were homogeneously mixed at 80 o C, and then capillary-filled into the 15 μm-thick cells treated with anti-parallel alignment at room temperature. Upon exposure to a 480 nm laser (5.0 mW cm -2 ) though the photomask for 30 min at 40 o C, the C6M monomers were trigger by free radical polymerization to form the liquid-crystalline polymer networks with the arrangement of CLCs. After photopolymerization, the exposed and unexposed areas exhibit unapparent difference in the cells.