posted on 2023-02-17, 04:43authored byPayel Khanra, Ajeet Kumar Singh, Lisa Roy, Anindita Das
This study unravels the intricate kinetic and thermodynamic
pathways
involved in the supramolecular copolymerization of the two chiral
dipolar naphthalene monoimide (NMI) building blocks (O-NMI and S-NMI), differing merely by a single heteroatom
(oxygen vs sulfur). O-NMI exhibits distinct supramolecular
polymerization features as compared to S-NMI in terms
of its pathway complexity, hierarchical organization, and chiroptical
properties. Two distinct self-assembly pathways in O-NMI occur due to the interplay between the competing dipolar interactions
among the NMI chromophores and amide–amide hydrogen (H)-bonding
that engenders distinct nanotapes and helical fibers, from its antiparallel
and parallel stacking modes, respectively. In contrast, the propensity
of S-NMI to form only a stable spherical assembly is
ascribed to its much stronger amide–amide H-bonding, which
outperforms other competing interactions. Under the thermodynamic
route, an equimolar mixture of the two monomers generates a temporally
controlled chiral statistical supramolecular copolymer that autocatalytically
evolves from an initially formed metastable spherical heterostructure.
In contrast, the sequence-controlled addition of the two monomers
leads to the kinetically driven hetero-seeded block copolymerization.
The ability to trap O-NMI in a metastable state allows
its secondary nucleation from the surface of the thermodynamically
stable S-NMI spherical “seed”, which leads
to the core-multiarmed “star” copolymer with reversibly
and temporally controllable length of the growing O-NMI “arms” from the S-NMI “core”.
Unlike the one-dimensional self-assembly of O-NMI and
its random co-assembly with S-NMI, which are both chiral,
unprecedentedly, the preferred helical bias of the nucleating O-NMI fibers is completely inhibited by the absence of stereoregularity
of the S-NMI “seed” in the “star”
topology.