Host–Guest Chemistry in Integrated Porous Space Formed by Molecular Self-Assembly at Liquid–Solid Interfaces

Abstract

Host-guest chemistry in two-dimensional (2D) space, that is, physisorbed monolayers of a single atom or a single molecular thickness on surfaces, has become a subject of intense current interest because of perspectives for various applications in molecular-scale electronics, selective sensors, and tailored catalysis. Scanning tunneling microscopy has been used as a powerful tool for the visualization of molecules in real space on a conducting substrate surface. For more than a decade, we have been investigating the self-assembly of a series of triangle-shaped phenylene-ethynylene macrocycles called dehydrobenzo[12]annulenes (DBAs). These molecules are substituted with six alkyl chains and are capable of forming hexagonal porous 2D molecular networks via van der Waals interactions between interdigitated alkyl chains at the interface of organic solvents and graphite. The dimension of the nanoporous space or nanowell formed by the self-assembly of DBAs can be controlled from 1.6 to 4.7 nm by simply changing the alkyl chain length from C to C. Single molecules as well as homoclusters and heteroclusters are capable of coadsorbing within the host matrix using shape- and size-complementarity principles. Moreover, on the basis of the versatility of the DBA molecules that allows chemical modification of the alkyl chain terminals, we were able to decorate the interior space of the nanoporous networks with functional groups such as azobenzenedicarboxylic acid for photoresponsive guest adsorption/desorption or fluoroalkanes and tetraethylene glycol groups for selective guest binding by electrostatic interactions and zinc-porphyrin units for complexation with a guest by charge-transfer interactions. In this Feature Article, we describe the general aspects of molecular self-assembly at liquid/solid interfaces, followed by the formation of programmed porous molecular networks using rationally designed molecular building blocks. We focus on our own work involving host-guest chemistry in integrated nanoporous space that is modified for specific purposes.

Probing functional self-assembled molecular architectures with solution/solid scanning tunnelling microscopy

“…Recent reviews have described a range of demonstrated strengths of solution/solid STM as an experimental probe, including investigations of molecular reactivity 31 and patterning, 32 elucidation of kinetic and thermodynamic processes, 24 and unravelling the details of programmed host/guest assembly in porous molecular networks. 33 Here, we focus on an emerging application of solution/solid STM: its utility as an enabling technology for practical applications of solution-processed self-assembled molecular structures.…”

Bottom-Up Self-Assembled Supramolecular Structures Built by STM at Solid/Liquid Interface

“…Two methodologies are available for fabrication of nanoporous surfaces depending on the types of building blocks: intrinsic and extrinsic. [28,29]. Nanoporous monolayers developed with intrinsic building blocks are founded on macrocyclic molecular structures that are pre-designed with a hollow centre and synthesised beforehand and with specific physical and chemical characteristics.…”

“…The most used extrinsic building blocks are as trimesic acid (TMA) [30,31], dehydrobenzo [12]annulene (DBA) [32][33][34][35][36] and decycanooligophenylenes [37,38]. They form hexagonal nanopores in which pore size may be modulated by changing the chemical composition of each building block [28][29][30]34]. These are the most attractive systems, since it is possible to modify the pore properties using specific building blocks to obtain a desired purpose.…”

“…To ensure that the deposited molecules retain a specific packing arrangement avoiding pore hinderance or self-assembly of flat-lying monolayers it is important to know the interactions between molecules and surface. Table 1 resumes the main interactions of these extrinsic building blocks that were analyzed in nanoporous self-assembled networks [39]. The solvent can play an important role in the formation of nanoporous networks.…”

Formation of multicomponent 2D assemblies of C2v-symmetric terphenyl tetracarboxylic acid at the solid/liquid interface: recognition, selection, and transformation

“…Two-dimensional supramolecular self-assembly has received a great deal of attention owing to its potential applications in nano-patterning and host-guest structures on surfaces at the molecular level over recent years. [1][2][3][4][5][6] The hydrogen bonding between carboxylic acid groups is the most extensively studied assembly motif for construction of supramolecular assemblies. [7][8][9] Compared with other supramolecular interaction, hydrogen bonding exhibits both high selectivity and directionality, and is suitable to create novel nano-patterning structures with high predictivity.…”