Synthesis and thermotropic properties of new green electrochromic ionic liquid crystals

Novel 1,1′-bis(4-alkylphenyl)-[4,4′-bipyridine]-1,1′-diium salts, with alkyl chains of different lengths (8, 10 and 14 carbon atoms) and with different counteranions (Cl-, NTf2-, OTf-, OTs-, PF6-, BPh4-), have been prepared and fully characterized for their thermotropic behavior by polarized optical microscopy (POM), and calorimetric measurements. Almost all the synthesized compounds showed a high thermal stability, a wide temperature range of liquid-crystalline mesophase and, for some of them, the LC transition temperatures were relatively low. These compounds also exhibited electrochromic properties, which have been studied both in solution and in the LC phase, making the new materials very interesting for different opto-electronic applications.