Reversible Color Transitions of Polydiacetylene Under Heating-UV Irradiation Cycles

Polydiacetylene (PDA) is an attractive polymer material due to its unique chromatic and fluorogenic transitions by external stimuli as temperature, pH, solvent, ligand-receptor, etc. However, the irreversible optical transitions of PDA make it be used as a single-use disposable materials, limiting the application to biosensor. Our study suggests a systematic approach to manipulate the degree of reversible color transitions of PDA depending on the binding strength between PDA headgroups. The reversibility of PDA is closely related to hydrogen bond strength and ionic interactions between the headgroups of PDA. Three types of PDA vesicles were prepared by using carboxyl-terminated diacetylene monomer (PCDA), amine-terminated diacetylene monomer (PCDA-EDA; PCDA-ethylenediamine), and both monomers. The PDA composed of both carboxyl- and amine-terminated monomers (poly(PCDA/PCDA-EDA)) at a molar ratio of 1:1 exhibited noticeable chromatic reversibility with colorimetric response (CR) values between <i>ca</i>. 84-91% and <i>ca</i>. 24-61% under heating-UV irradiation cycles. The changes in the backbone structure and hydrogen bond strength influencing the reversible color transitions of PDA were confirmed by Raman and Fourier transform infrared (FT-IR) spectroscopies, respectively. Furthermore, structural characterizations such as dynamic light scattering (DLS) and scanning electron microscopy (SEM) showed that morphological changes of PDA are closely connected to their color response. These results demonstrate that the hydrogen bond strength and ionic interactions of PDA with different terminal functional groups play an important role in the controllable colorimetric reversibility of PDA, which can ultimately be applied to the development of recyclable PDA sensors.