Polydiacetylenes (PDAs) are unique micelle type polymeric, molecular system, which are containing diacetylene functional group in molecules. These specific vesicles could be polymerized from diacetylene containing linear molecules with UV irradiation and ultrasonic treatments in aqueous media. And this photopolymerization of diacetylene forms an array of acetylene-ethylene backbone with delocalized π-electrons. The polymerized vesicle solution with these compounds showed blue to purple or red or yellow colorimetric transitions by external stimuli such as temperature, pH, molecular or ion contact, solvent, and etc. Since the color changes of PDAs are detectable by naked eyes, it has been developed label free sensor for variable stimuli.¹

Recently we have designed and synthesized PCDA (pentacosa-10,12-diynoylic acid) derivatives, which have different side alkyl chain lengths of head group. These series of PCDA derivatives showed different colors (blue, purple, red and yellow) at room temperature without external stimuli. In addition, we have performed that the functionalization of PCDA molecules with a series of polar or non-polar functional groups. The polarity-controlled PCDA molecules show an elevation of color-changing (blue to purple and red) temperature. We believe that these two experimental finding allow many insights to understand color changing mechanism of PDAs.²