Morphological Transformation between Nanocoils and Nanoribbons via Defragmentation Structural Rearrangement or Fragmentation-recombination Mechanism

Kinetic control over the assembly pathways towards novel metastable functional materials or far-from-equilibrium systems has been much less studied compared to the thermodynamic equilibrium self-assembly. Herein, we report the distinct morphological transformation between nanocoils and nanoribbons in the self-assembly of unsymmetric perylene diimide (PDI) molecules. We demonstrate that the morphological transformation of the kinetically trapped assemblies into the thermodynamically stable forms proceeds via two distinct mechanisms, i.e., a direct structural rearrangement (molecule 1 or 2) and a fragmentation-recombination mechanism (molecule 4), respectively. The subtle interplay of the steric hindrance of the bulky substituents and the flexibility of the linker structure between the bulky moiety and the perylene core was demonstrated to enable the effective modulation of the energetic landscape of the assemblies and thus modulation of the assembly pathways. Herein, our work presents a new approach to control the self-assembly pathways and thereby can be used to achieve novel far-from-equilibrium systems.


Materials
All reagents and solvents were obtained from commercial suppliers and used as received unless otherwise noted.
(3-((3-methoxybenzyl)oxy)phenyl)methanamine (1c). 1b (470 mg) was added to a solution of dichloromethane (5 mL) and trifluoroacetic acid (5 mL). The resulting solution was stirred for 3 h at room temperature, and then trifluoroacetic acid was removed by rotary evaporation. Saturated NaHCO3 solution (10 mL) was added to the residue and the resulting solution was extracted with dichloromethane (3 × 10 mL). The combined organic layers were dried over sodium sulfate, and concentrated under vacuum to afford compound 1c, which was not purified and used directly for the following reaction.

2-(2-((3-methoxybenzyl)oxy)phenyl)ethanamine (2c)
. 2b (420 mg) was added to a solution of dichloromethane (5 mL) and trifluoroacetic acid (5 mL). The resulting solution was stirred for 3 h at room temperature, and then trifluoroacetic acid was removed by rotary evaporation. Saturated NaHCO3 solution (10 mL) was added to the residue and the resulting solution was extracted with dichloromethane (3 × 10 mL). The combined organic layers were dried over sodium sulfate, and concentrated under vacuum to afford compound 2c, which was not purified and used directly for the following reaction.
(2-((3-methoxybenzyl)oxy)phenyl)methanamine (3c) 3b (520 mg) was added to a solution of dichloromethane (5 mL) and trifluoroacetic acid (5 mL). The resulting solution was stirred for 3 h at room temperature, and then trifluoroacetic acid was removed by rotary evaporation. Saturated NaHCO3 solution (10 mL) was added to the residue and the resulting solution was extracted with dichloromethane (3 × 10 mL). The combined organic layers were dried over sodium sulfate, and concentrated under vacuum to afford compound 3c, which was not purified and used directly for the following reaction.

2-(2-((3-methoxybenzyl)oxy)phenyl)ethanamine (4c)
4b (360 mg) was added to a solution of dichloromethane (5 mL) and trifluoroacetic acid (5 mL). The resulting solution was stirred for 3 h at room temperature, and then trifluoroacetic acid was removed by rotary evaporation. Saturated NaHCO3 solution (10 mL) was added to the residue and the resulting solution was extracted with dichloromethane (3 × 10 mL). The combined organic layers were dried over sodium sulfate, and concentrated under vacuum to afford compound 4c, which was not purified and used directly for the following reaction.  Figure S1. TEM image of nanocoils assembled from 1 at 6 h after beginning the selfassembly. Figure S2. TEM image of the intermediate morphology with partly coiled structure assembled from 1 at 1 h after beginning the self-assembly process (indicated by circles).    Figure S6. TEM imaging of the assemblies from 4 at different self-assembling time points: 5 min (a); 5 h (b); 24 h (c). Inset: length distribution of the formed assemblies (the length of more than 50 aggregates was measured), which clearly shows the aggregates elongated with time. Figure S7. TEM image of the intermediate morphology with shorter nanocoils structure assembled from 4 at 1 h after beginning the self-assembly process (indicated by red circle).