Anticooperative Supramolecular Oligomerization Mediated by V‐Shaped Monomer Design and Unconventional Hydrogen Bonds

Abstract

After more than three decades of extensive investigations on supramolecular polymers, strategies for selflimiting growth still remain challenging. Herein, we exploit a new V-shaped monomer design to achieve anticooperatively formed oligomers with superior robustness and high luminescence. In toluene, the monomer-oligomer equilibrium is shifted to the monomer side, enabling the elucidation of the molecular packing modes and the resulting (weak) anticooperativity. Steric effects associated with an antiparallel staircase organization of the dyes are proposed to outcompete aromatic and unconventional BÀ F•••HÀ N/C interactions, restricting the growth at the stage of oligomers. In methylcyclohexane (MCH), the packing modes and the anticooperativity are preserved; however, pronounced solvophobic and chain-enwrapping effects lead to thermally ultrastable oligomers. Our results shed light on understanding anticooperative effects and restricted growth in self-assembly.

Sterically Allowed H‐type Supramolecular Polymerizations

“…For some of the aggregates, complementary cooling studies were also possible (see the S.I.). The thermodynamic parameters could be derived by plotting the evolution of absorbance at a particular wavelength against the volume fraction of CH 2 Cl 2 at different concentrations and subsequent fitting to the solvent‐dependent model [26] . Thermodynamic analysis for 2AggA revealed a Gibbs free energy of Δ G 0 =−30.83 kJ mol −1 , and its formation follows the isodesmic mechanism (Figure 5a,e).…”

“…However, as these values largely depend on the concentration, this energy difference should be considered as a qualitative measure. On the other hand, disassembly of 3AggA and 3AggB can be probed independently using denaturation studies [26] . For both assembled states, direct disassembly to monomeric 3 is achieved by increasing the CH 2 Cl 2 volume fraction (Figure 5c,d).…”

“…On the other hand, disassembly of 3AggA and 3AggB can be probed independently using denaturation studies. [26] For both assembled states, direct disassembly to monomeric 3 is achieved by increasing the CH 2 Cl 2 volume fraction (Figure 5c,d). The plots of α agg vs. the volume fraction of CH 2 Cl 2 are non-sigmoidal (Figure 5g,h), indicating that both assemblies follow the cooperative mechanism.…”

“…The thermodynamic parameters could be derived by plotting the evolution of absorbance at a particular wavelength against the volume fraction of CH 2 Cl 2 at different concentrations and subsequent fitting to the solvent-dependent model. [26] Thermodynamic analysis for 2AggA revealed a Gibbs free energy of ΔG 0 = À 30.83 kJ mol À 1 , and its formation follows the isodesmic mechanism (Figure 5a,e). Thermodynamic analysis of 2AggB using similar denaturation (or alternatively thermal) approaches are not possible, as 2AggB always dissociates first into 2AggA prior to complete disassembly into monomeric 2 (Figure 5b,f, 4b and S6).…”

“…Accordingly, the supramolecular polymerization of two new BODIPY derivatives with phenyl (2) and mesityl (3) mesosubstituents was compared with that of a reference BODI-PY dye with a small meso-methyl substituent (1) that was previously demonstrated to form a single type of supramolecular polymer with H-type excitonic coupling in nonpolar media. [23] We observed that an increase of steric demand from methyl (1) to phenyl substitution (2) attenuates the aggregation propensity and causes pathway complexity [24] into two assembled states with one-dimensional morphology that do not interconvert over time: a Jtype aggregate driven by unconventional NÀ H•••FÀ B hydrogen bonding interactions [25,26] that is stable at higher temperatures and a more stable H-type aggregate stabilized by NÀ H•••O=C hydrogen bonds that exists at lower temperatures. A further increase of the steric demand from phenyl (2) to mesityl (3) also leads to two distinctly stable H-and Jtype supramolecular polymers, which are now both stabilized by NÀ H•••O=C hydrogen bonds.…”