Molecular engineering in 2D surface covalent organic frameworks: Towards next generation of molecular tectons - A mini review

Molecular engineering on surface has been revolutionized by the possibility to create covalent connections between molecular tectons. Following the pioneering works on supramolecular structures and their triumphal developments during a decade, covalent organic frameworks on surface open up new routes towards robust and regular porous macromolecular structures usable in practical applications such as molecular electronics, energy conversion or catalysis. Metal surfaces can be also be decorated with semiconducting organic structures, widening the scope of applicability of these polymer-modified surfaces. If the first generation of molecular building blocks was designed so that the functional groups were introduced for a specific reactivity, recently, a breakthrough has been achieved in 2016 and 2017 with the almost simultaneous reports of ENA and INDO4 capable to initiate different reaction pathways depending of the surface topography or the surface coverage. Prior to these two works, in 2015, another exciting candidate (i.e. TAPB) exhibiting however a more limited range of reactivity than ENA or INDO4 was reported, its reactivity being based on the presence of acetyl end-groups. In this minireview, the intriguing properties of these unique building blocks are presented.