Recently, a paper of Prof. Weihong Zhu group, “Separation of Photoactive Conformers Based on Hindered Diarylethenes: Efficient Modulation in Photocyclization Quantum Yields” has been published on Angewandte Chemie (Angew. Chem. Int. Ed. 2014, 53, 4603–4607, http://onlinelibrary.wiley.com/doi/10.1002/anie.201310438/full). In this work, a new photochromic diarylethene (DAE) system with high photocyclization quantum yields (Φo-c) was achieved.

    DAEs bestow two conformers as parallel conformation (p-) and anti-parallel conformation (ap-). Since the photochromic reaction can only result from the ap- conformation, the Φo-c in conventional DAEs is usually limited to 50%. With critical concerns on the photo-switching efficiency for practicable device application, it is pivotal to tailor the equilibrium between p- and ap- conformations for an increase in the photocyclization quantum yield. To reach this goal, the group of Prof. Zhu for the first time separated the p- and ap- conformers with high thermal stability employing the steric hindrance originated from the extended ethene bridge and large aryl groups. The ap- conformers showed double enhancements in Φo-c with solvent independency and well thermal bistability. Furthermore, the Φo-c was promoted up to 90.6%, upon suppressing intramolecular charge transfer. This work made important foundations on building novel photochromic systems with high photosensitivity, and benefited for the studies on hindered DAEs with internal chirality in the future.

    The research was completed by doctoral student, Wenlong Li and master student, Changhong Jiao under the direction of Prof. Weihong Zhu, and financially supported by National 973 Program (No. 2013CB733700), NSFC/China, NSFC for Distinguished Young Scholars (Grant No. 21325625).