Revising Complex Supramolecular Polymerization under Kinetic and Thermodynamic Control

Abstract

Pathway complexity, hierarchical organization, out of equilibrium, and metastable or kinetically trapped species are common terms widely used in recent, high-quality publications in the field of supramolecular polymers. Often, the terminologies used to describe the different self-assembly pathways, the species involved, as well as their relationship and relative stability are not trivial. Different terms and classifications are commonly found in the literature, however, in many cases, without clear definitions or guidelines on how to use them and how to determine them experimentally. The aim of this Minireview is to classify, differentiate, and correlate the existing concepts with the help of recent literature reports to provide the reader with a general insight into thermodynamic and kinetic aspects of complex supramolecular polymerization processes. A good comprehension of these terms and concepts should contribute to the development of new complex, functional materials.

Keywords: hierarchy; out-of-equilibrium systems; pathway complexity; self-assembly; supramolecular polymers.

Figure 1

a) Chemical structure of amphiphile 1. b) Time‐dependent DLS measurement showing the transformation of initially formed spherical micelles into cylindrical micelles. c) TEM image of an aged solution showing cylindrical micelles. Adapted from Ref. 16 with permission. Copyright 2005 American Chemical Society.

Figure 2

Chemical structure of amphiphilic Pt^II complex 2 and its pathway‐dependent self‐assembly. Adapted from Ref. 17 with permission. Copyright 2011 Wiley‐VCH.

Figure 3

a) Chemical structure of 3. b) Plots of CD signal versus time in stopped‐flow kinetic experiments. c) Schematic illustration of the competitive aggregation pathways of 3. Adapted from Ref. 20 with permission. Copyright 2012 Springer Nature.

Figure 4

Energy landscapes illustrating the different concepts for pathway/aggregate characterization: a) dissipative versus non‐dissipative and equilibrium versus non‐equilibrium states; b) competitive pathways; c) consecutive pathways; d) system of higher complexity with a hierarchical kinetic pathway and the possibility of living SP by a seeded‐growth approach.

Figure 5

a) Structure of merocyanine dye 4 and b) its solvent‐dependent UV/Vis spectra. Hierarchical self‐assembly by dimerization and subsequent growth into c) helical fibrils that d) form rods that e) ultimately intertwine. Adapted from Ref. 39 with permission. Copyright 2003 Wiley‐VCH.

Figure 6

a) Structure of photochromic unit 5 and b) corresponding CD spectra recorded upon hierarchical SP into c) nanotoroids, d) nanotubes, and e) eventually chiral single and double helices, as observed by AFM. Adapted from Ref. 40 with permission. Copyright 2012 American Chemical Society.

Figure 7

a) Chemical structure of OPE 6 and c) its hierarchical self‐assembly. b) Temperature‐induced disassembly curve of P‐type superhelices that converges with the curve obtained for M‐type helices. Adapted from Ref. 41 with permission. Copyright 2017 Wiley‐VCH.

Figure 8

a) Chemical structure of 7 and b) its competitive J‐ versus H‐type aggregation. c) Cooling (pink) and heating (green) curves for the two possible pathways. d) Four‐cycle LSP through seeded growth from J‐ to H‐aggregates. Adapted from Ref. 43 with permission. Copyright 2014 Springer Nature.

Figure 9

a) Chemical structure of PBI 8 and the equilibrium between the active and dormant conformation. b) Thermal hysteresis during the SP of 8 in toluene and MCH/toluene (2:1 v/v). c) Chemical structures of corannulene derivatives 9_M (monomer) and 9_I (initiator). A schematic representation of LSP of dormant 9_M initiated through addition of 9_I inducing H‐bond reorganization is also shown. Adapted from Ref. 34 with permission. Copyright 2015 American Chemical Society and from Ref. 32. Copyright 2015 AAAS.

Figure 10

a) Chemical structure of OPE‐Pt^II complex 10. b) UV/Vis spectra of the monomer (M), as well as concomitant aggregates (A and B). c) Time‐dependent UV/Vis spectra showing the transformation of A into B via M. d) Phase diagram and energy landscape showing the competitive pathways. Adapted from Ref. 45 with permission. Copyright 2019 American Chemical Society.

Figure 11

a) Chemical structure of Pt complex 11 and schematic representation of its self‐assembly pathways. b) Fluorescence confocal microscopy images depicting the evolution (from left to right) of A into B and C. Adapted from Ref. 46 with permission. Copyright 2015 Springer Nature.

Figure 12

a) Chemical structure of ZnPs 12 and 13 as well as b) the energy landscape depicting one‐ and two‐dimensional LSP along thermodynamic and kinetic pathways. Adapted from Ref. 27 with permission. Copyright 2016 Springer Nature.

Figure 13

a) Chemical structure of PBI 14 and b) its self‐assembly into three different supramolecular polymorphs Agg 1—Agg 3. c) Qualitative 3D energy landscape of 14 illustrating its SP pathways. Parameter Q represents the lowest‐energy transformation pathway at a given concentration. Adapted from Ref. 47 with permission. Copyright 2019 American Chemical Society.