The Current Understanding of how 2D Polymers Grow Photochemically

2D polymers are a relatively new class of macromolecules. Therefore, it is not astounding that so far research focused on how to provide access to this intriguing class of organic 2D materials, how to prove their existence, and how to assess their structural quality. Studies concerning the formation mechanism are comparatively scarce. We here collect and compare all the mechanistic information available for 2D polymer synthesis by photochemical means and point towards research directions to be followed in order to advance the fundamental understanding and, thus, fast development of this field. Because the two current starting situations for the photochemical synthesis of 2D polymers are layered single crystals and surface‐supported monolayers, the prominent analytical tools are X‐ray diffraction (XRD), local vibration spectroscopy, e. g. tip enhanced Raman spectroscopy (TERS), and scanning probe microscopy (SPM), e. g. low temperature scanning tunnelling microscopy (LT STM) in ultra‐high vacuum (UHV), but also atomic force microscopy (AFM). With their advantages and shortcomings, they will therefore play an important role throughout this mini review. The reaction venues are different, but the synthetic targets are the same: single‐layered long‐range ordered 2D polymer molecules. This Minireview collects and compares the first experiments helping to unravel the underlying mechanisms that afford these unique macromolecules by the controlled formation in the order of millions of covalent bonds per μm2 both in layered single crystals and on solid surfaces.