Modulating Large‐Area Self‐Assembly at the Solid–Liquid Interface by pH‐Mediated Conformational Switching

Abstract

Dynamic surfaces: The conformational transition of 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (BTP) derivatives, triggered by a change in pH, has been observed with a sub-nm resolution by STM at the solid-liquid interface. Upon addition of trifluoroacetic acid two different BTP molecules, each forming a highly ordered physisorbed monolayer, underwent significant conformational changes from their "rosette" to their "tetragon" forms, as reflected in dramatically altered 2D self-assembly over large areas extending over hundreds of nanometers (see graphic).

Designing Structural Motifs for Clickamers: Exploiting the 1,2,3‐Triazole Moiety to Generate Conformationally Restricted Molecular Architectures

“…General design considerations: In our previous work, [12,[14][15][16][17] solely the BTP motif was used, which offers conformational restriction only about the C(4)-aryl connection, readily achieved by means of a click reaction of bis(ortho-ethynyl)pyridines with aromatic azides. Initial attempts to also bias the N(1)-aryl connection failed because bis(ortho-azido)pyridines could not be prepared.…”

“…By exploiting the highly efficient copper-catalyzed "click" reaction not only to efficiently connect monomer units but also to incorporate the triazole unit to induce secondary structure formation, we have recently developed the 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (BTP) motif [12,13] and investigated BTP-derived scaffolds for responsive folding in solution, [14] as ligands [15] and metallosupramolecular gels, [16] as well as at the liquid-solid interface. [17] To apply our strategy for the design of new backbones, we have engaged in a detailed study of various 1,2,3-triazole-connected (hetero)aromatic systems. Here, we report on the synthesis of these new folding motifs and discuss the influence of different heteroatoms-that is, N-, O-, F-substitution-on the conformational preference about both the N(1)-aryl of the triazole as well as the C(4)-aryl bonds.…”

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

“…This reorganisation (from 'rosette' to 'tetragon' motifs) of the meta-isomer of 59b was possible to observe in real-time over about 20 minutes. 160 Upon similar acidification of the meta-isomer of 60, the conformation of the compound was also concluded to invert, with previous 'disordered' domains reorganizing into 'lamellar' assemblies. 112 Related shape-persistent flat dendrimers 61 and 62 behaved as disc-like amphiphiles, which stacked into cylindrical nanorods.…”

“…129 Hecht and co-workers described the formation of first and second generation btp dendrons 59 and 60, which were studied upon self-assembly at the solid-liquid interface upon physisorption on highly oriented pyrolytic graphite (HOPG). 112,160 The three regioisomers of 59b displayed ordered 2D self-assembly patterns in STM images, however, pronounced effects upon the selfassembly of the monolayers were noted as a result of differing substitution patterns of the phenyl rings. Protonation of 59 upon addition of trifluoroacetic acid caused structural reorganisation to occur at the solid-liquid interface; the authors concluded this was as a result of interconversion from anti-anti ('kinked') to syn-syn ('extended') geometry.…”

2D Structural Modulation by Odd-Even Effect of Alkyl Chains Revealed by Scanning Tunneling Microscopy at Solid/Liquid Interface

“…1). The notable advantages of using STM at the solid/liquid interface are: (1) the relationship between the molecular structure with supramolecular interaction sites and the resulting 2D ordering can be resolved in the molecular level, [14][15][16][17][18][19] (2) postreaction, such as metallation, blending, UV irradiation, etc., is possible on the surface, [26][27][28][29] and thereby (3) dynamic 2D structural changes can be followed in situ on HOPG. [30][31][32] In this review, we summarize our recent progress on the formation of 2D structures, and particularly discuss the oddeven effect of alkyl tails introduced on porphyrin derivatives, isobutenyl compounds and bipyridine derivatives.…”