1 State Key Laboratory of Bioinspired Interfacial Materials Science, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou 215123, PR China. ivasenko@suda.edu.cn.
2 Division of Molecular Imaging and Photonics, Department of Chemistry, KU Leuven, Celestijnenlaan 200 F, 3001 Leuven, Belgium. steven.defeyter@kuleuven.be.
3 i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, PR China.
4 Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec H4B 1R6, Canada.

Gentle annealing and photopolymerization under inert atmospheres strongly enhance the quality of polydiacetylene monolayers. These simple measures not only triple the average degree of polymerization but also alter the preferred photoexcitation mode and cause pronounced nano-alignment during the early stages of polymerization.