Effects of alkyl chain length on thermochromism of polydiacetylene containing two amide groups

Abstract

Five symmetrical and six unsymmetrical diyndiamide monomers were prepared. Their thermochromic properties were investigated in order to probe the effects of methylene units within the linker (x) and hydrophobic tail (y) on thermochromic reversibility. All synthesized monomers were dispersed well in Milli-Q water by ultrasonication. The dispersion could be converted to blue sols of polydiacetylenes (PDA) via UV irradiation. In case of PDA derived from symmetrical diyndiamides, high color transition temperature (CTT) (70-80 °C) and high degree of color reversibility (%DR = 88-93) were observed with PDAs containing even methylene linkers while the PDAs with odd methylene linkers showed low CTT (35-45 °C) and low degree of color reversibility (%DR = 20-65). For the PDAs derived from unsymmetrical diyndiamide, %DR of the PDAs increased upon raising the number of methylene units within the hydrophobic tail (y). The results indicate that the number of methylene units play an important role in thermochromic reversibility providing the strategy in molecular design for thermal sensor development.