Thermodynamic Self-Assembly of Two-Dimensional π-Conjugated Metal–Porphyrin Covalent Organic Frameworks by “On-Site” Equilibrium Polymerization

Abstract

Two-dimensional pi-conjugated metal-porphyrin covalent organic frameworks were produced in aqueous solution on an iodine-modified Au(111) surface by "on-site" azomethine coupling of Fe(III)-5,10,15,20-tetrakis(4-aminophenyl)porphyrin (FeTAPP) with terephthal dicarboxaldehyde and investigated in detail using in-situ scanning tunneling microscopy. Mixed covalent organic porphyrin frameworks consisting of FeTAPP and metal-free TAPP (H2TAPP) were prepared through simultaneous adsorption in a mixed solution as well as partial replacement of FeTAPP by H2TAPP in an as-prepared metal-porphyrin framework. In the mixed framework, the relative distribution of FeTAPP to H2TAPP was not random and revealed a preference for homo-connection rather than heteroconnection. The construction of substrate-supported, pi-conjugated covalent frameworks from multiple building blocks, including metal centers, will be of significant utility in the design of functional molecular nanoarchitectures.

Covalent organic frameworks based on Schiff-base chemistry: synthesis, properties and potential applications

“…69 The self-assembly of the sophisticated covalent nanostructures on well-defined surfaces in aqueous solution can be achieved by reversible equilibrium ''on-site'' polymerization at the solid-liquid interface, whereby aromatic building blocks spontaneously and selectively form linkages consisting of metal-free porphyrin and bifunctional aromatic linkage molecules. 69 The self-assembly of the sophisticated covalent nanostructures on well-defined surfaces in aqueous solution can be achieved by reversible equilibrium ''on-site'' polymerization at the solid-liquid interface, whereby aromatic building blocks spontaneously and selectively form linkages consisting of metal-free porphyrin and bifunctional aromatic linkage molecules.…”

Self-assembled π-conjugated macromolecular architectures — A soft solution process based on Schiff base coupling

“…Specifically, the use of aromatic primary amine and aromatic aldehyde units as complementary reactive substituents for aromatic Schiff base (also known as imine or azomethine) coupling. [49][50][51][52] The reaction between primary amines and aldehydes can be achieved spontaneously even in aqueous media at room temperature. The Schiff-base reaction has been widely applied for the synthesis of discrete supramolecules and 2-D [53] as well as 3-D nanoarchitectures.…”

“…49. Copyright 2011 American Chemical Society.2-4 Porphyrin based 2-D mesh frameworks and supramolecular arrays of discrete reaction productsFollowing the "on-site" successive polycondensation of π-conjugated 1-D polymeric systems, the ability to apply this synthetic methodology toward the fabrication of 2-D π-conjugated supramacromolecular frameworks was pursued [49,51]. Compared with chain polymerization on substrate surfaces such as polyacetylene and polythiophene initiated by local bias[56] or electrochemical control[57,58], surface-mediated successive polymerization enables the preparation of sophisticated cross-linked nanostructures like meshes or honeycombs by varying the number and relative arrangements of predefined reaction points, as for non-covalent hydrogen bonded network systems,15,20-tetrakis-(4-aminophenyl)-21,23H-porphyrin (TAPP) provides adlayers for nanomesh frameworks.…”

Persistent Homology to Quantify the Quality of Surface‐Supported Covalent Networks

“…A large variety of surface‐supported 2D networks were fabricated in ultrahigh vacuum (UHV) environment or at the liquid‐solid interface . In the latter case thermodynamic equilibrium conditions can be reached and extended well‐ordered networks can be formed.…”