**Corentin Pigot \* and Frédéric Dumur \***

Aix Marseille Univ, CNRS, ICR UMR 7273, F-13397 Marseille, France

**\*** Correspondence: pigotcorentin2@gmail.com (C.P.); frederic.dumur@univ-amu.fr (F.D.); Tel.: +33-(0)4-91-28-27-48 (F.D.)

Received: 17 January 2019; Accepted: 19 February 2019; Published: 22 February 2019

**Abstract:** The fabrication of macromolecular organic structures on surfaces is one major concern in materials science. Nanoribbons, linear polymers, and porous nanostructures have gained a lot of interest due to their possible applications ranging from nanotemplates, catalysis, optoelectronics, sensors, or data storage. During decades, supramolecular chemistry has constituted an unavoidable approach for the design of well-organized structures on surfaces displaying a long-range order. Following these initial works, an important milestone has been established with the formation of covalent bonds between molecules. Resulting from this unprecedented approach, various nanostructures of improved thermal and chemical stability compared to those obtained by supramolecular chemistry and displaying unique and unprecedented properties have been developed. However, a major challenge exists: the growth control is very delicate and a thorough understanding of the complex mechanisms governing the on-surface chemistry is still needed. Recently, a new approach consisting in elaborating macromolecular structures by combining consecutive steps has been identified as a promising strategy to elaborate organic structures on surface. By designing precursors with a preprogrammed sequence of reactivity, a hierarchical or a sequential growth of 1D and 2D structures can be realized. In this review, the different reaction combinations used for the design of 1D and 2D structures are reported. To date, eight different sequences of reactions have been examined since 2008, evidencing the intense research activity existing in this field.

**Keywords:** on-surface reaction; stepwise growth; sequential growth; hierarchical growth; macromolecular organic structures; surface covalent organic framework; nanoribbons; macrocycles; coordination polymers
