Synthesis and thermal transition behaviour of new reactive mesogens with propiolate (-C≡C-COO-) linkages

Abstract

New diacrylate reactive mesogens (Ph1 and Fl1) with propiolate (-C≡C-COO-) linkages between the aromatic rings have been synthesised. Either 2-methylphenyl-1,4-diol (Ph) or 9,9-diethylfluorene-2,7-diol (Fl) was used as a central core unit. The mesomorphic properties were then compared with those of the homologues Ph2 and Fl2, which contain ester (-COO-) linkages. The new compounds Ph1 and Fl1 exhibited an increased nematic mesophase window that was probably caused by the additional triple bond present in the propiolate (-C≡C-COO-). Interestingly, the homologues Fl1 and Fl2, which were based on a 9,9-diethylfluorene-2,7-diol (Fl) core unit, showed a polymorphism. Furthermore, double clearing behaviour was observed by polarised optical microscopy for the compound Fl2, which to the best of our knowledge is the first example of such behaviour in reactive mesogens.

Keywords:

• reactive mesogen
• propiolate
• mesomorphism
• nematic phase
• polymorphism
• double clearing behaviour

Acknowledgements

This research was supported by Korean Ministry of Knowledge Economy (Fundamental R&D program for Core Technology of Materials) and by KRICT's own project. The author would like to thank the referee for helpful comments.