Bottom-up multicomponent molecular self-assembly is an efficient approach
to fabricate and manipulate chiral nanostructures and their chiroptical activi
ties such as the Cotton effect and circular polarized luminescence (CPL).
However, the integrated coassembly suffers from spontaneous and inherent
systematic pathway complexity with low yield and poor fidelity. Consequently,
a rational design of chiral self-assembled systems with more than two
components remains a significant challenge. Herein, a modularized, ternary
molecular self-assembly strategy that generates chiroptically active materials
at diverse hierarchical levels is reported. N-Terminated aromatic amino acids
appended with binding sites for charge transfer and multiple hydrogen bonds
undergo the evolution of supramolecular chirality with unique handedness
and luminescent color, generating abundant CPL emission with high lumines
cence dissymmetry factor values in precisely controlled modalities. Ternary
coassembly facilitates high-water-content hydrogel formation constituted by
super-helical nanostructures, demonstrating a helix to toroid topological tran
sition. This discovery would shed light on developing complicated multicom
ponent systems in mimicking biological coassembly events.
systems, thermodynamic equilibrium and
non-equilibrium aggregates coexist, origi
nated from on and off-pathways.[8]
The
systematic pathway complexity would be
magnified dramatically in case of mul
tiple constituent self-assembly supported
by weak forces excluding metal–ligand
coordination.[9,10]
Two-component systems
suffer from mixed coassembly and self
sorting pathways, depending on the non
covalent binding competition and other
factors.[11,12]
For a further consideration,
there would be more than 20 possible
pathways or combinations in a ternary
system, and the number would rise to
≈200 for a quadruple component system.
Although artificial multiple constituent
systems (such as ternary and quadruple
systems) possess advantages in synthe
sizing soft materials with advanced pho
tophysical properties in a more precise
manner, such significant systematic com
plexity brings along great challenges.[13–15]
To overcome high systematic pathway complexity and fab
ricate synergistically integrated soft materials that beyond two
components, in this work, we employed two independent non
covalent interactions including CT[16]
and duplex hydrogen
bonding interactions among N-terminated pyrene amino acids
(namely PF and PV),[17]
1,3,5-tri(1H-benzo[d]imidazol-2-yl)
benzene (TBIB) and 1,2,4,5-tetracyanobenzene (TCNB) for
multicomponent molecular self-assembly (Figure 1). We estab
lished a general principle that multi-constituent molecular self
assembly could be modularized as different parts with distinct
functions.[18–20]
In this case, PF and PV (module A) are primary
building blocks with chiral centers and binding sites to the other
modules, where TBIB (module B) and TCNB (module C) could
selectively bind to module A to allow for rational manipulation
of modularized coassemblies via distinct attractive and repulsive
forces. Molecular module ABC is not a mutual binding system,
which has specific directional interactions upon noncovalent
combination. Module A could bind to A, B, and C primarily via
π–π stacking, duplex hydrogen bonding, and charge transfer
(CT) interactions, generating functional chiroptical materials
of AA, AB, and AC, respectively. However, due to the lack of
sufficient weak interactions between TCNB and TBIB, the BC
complexation is ruled out, avoiding unfavorable competitive
pathways. For PV, it has the propensity to form ABC type ternary
coassembly via duplex hydrogen bonding and CT interactions.
The hierarchical integration allows for flexible synthesis
of chiroptical materials with fine tailored Cotton effects,
Q3
Small 2020, 2002036
UNCORREC
