Hierarchic Self-Assembly of Nanoporous Chiral Networks with Conformationally Flexible Porphyrins

Abstract

We report the hierarchic design of homochiral 2D nanoporous networks under ultrahigh vacuum conditions on the Ag(111) surface by using a flexible porphyrin derivative as a primary unit. The conformational adaptation of the molecular module gives rise to two enantiomers upon 2D confinement, which self-assemble in enantiopure clusters made of three molecules reflecting chiral recognition, which constitute the secondary supramolecular building block mediating the formation of the tertiary complex open networks. Our results show that the creation of homochiral superstructures based on the hierarchical assembly of conformationally flexible molecular components constitutes a unique pathway toward the design of novel and functional chiral structures.

Sequential nested assembly at the liquid/solid interface

“…4, a purely rotational step is not possible for sterical reasons as indicated by the dotted circle in structure i if one assumes that the molecule is rigid and the molecule is confined to two dimensions, i.e., all parts of the molecule are always in contact with the surface. Even if one takes into account that the ethynyl bonds exhibit considerable flexibility, [63][64][65][66] they would have to be deformed to an extent (more than 60°) which seems unreasonable (structure ii). Including the third dimension by allowing the molecule to partially detach, the deformation of the molecule during a rotational step can be limited to its normal flexibility by one arm passing above a PTCDI molecule (structure iii).…”

Imaging on-surface hierarchical assembly of chiral supramolecular networks

“…13,[24][25][26][27] Recently, special attention has been devoted to systems presenting a hierarchical chirality transfer, which reveals the presence of sequentially-activated enantioselective mechanisms. 24,[28][29][30][31][32][33][34][35] Blüm et al 28 reported the fascinating case of rubrene (C 42 H 28 ) assembling into pentagonal structures, which act as building blocks for a second generation decagons. Interestingly, both the resulting supramolecular structures are enantiopure, indicating the conservation of chirality during the coordination.…”

“…Hierarchical organization can also be steered through metal-ligand interactions, where the presence of metal adatoms imposes distinctive multilevel binding processes. 24,33 Furthermore, sequential self-assembly of nanoporous homochiral networks has been recently observed using porphyrin derivatives, 29 representing an appealing platform for the realization of flexible functional materials. However, the atomic-scale mechanisms driving molecular recognition in hierarchical assemblies are yet to be clarified and the factors governing the enantioselectivity of these processes are largely unknown, limiting the possibility to design a priori tailored molecular units with programmed functionalities.…”

Self-assembly of iron TCPP (meso-tetra(4-carboxyphenyl)porphyrin) into a chiral 2D coordination polymer

“…This is the reason why synthetic metalloporphyrin complexes are often used as analogues of natural systems found in photosynthesis, oxygen carriers, and catalysts [5] [9][10][11][12][13][14]. For instance, these systems are used to understand the mechanism of electron transfer through intermolecular interactions, and some works show that efficient energy transfer may occur across the intermolecular bonds [15][16][17][18][19].…”