Highly Efficient Preparation of Single-Layer Two-Dimensional Polymer Obtained from Single-Crystal to Single-Crystal Synthesis.

A two-dimensional polymer (2DP) single crystal (T-2DP) with submillimeter size was synthesized by single-crystal to single-crystal transformation based on photochemical [2 + 2]-cycloaddition. A successful conversion from monomer to polymer was achieved in the single-crystal state. The structure information with an atomic resolution of both the monomer and 2DP was given through single-crystal X-ray diffraction. By simply treated with trifluoroacetic acid (TFA) under mild conditions, an unprecedented efficiency of exfoliation was achieved. The triazine core in T-2DP could be protonated by TFA, which resulted in a solution-like sample with >60% of monolayers. The size of the exfoliated monolayer reaches to several hundreds of μm2. This is another precious example of 2DP single crystal with nearly perfect structure and large enough size. The successful preparation of the highly desirable 2DP "solution" for a long time containing large sized and large amount of 2DP monolayers may open up new prospects for the basic properties study and the applications of 2DPs.