Hydrogen bonding reversibility in poly(10,12-pentacosadiynoic acid)/titanium dioxide composite analyzed by infrared spectroscopy

[Display omitted] •Polydiacetylene hydrogen bonding is monitored by infrared spectroscopy.•Blue to red change in polydiacetylene is not related to hydrogen bonding.•Chemical simulation describes thermal effect on polydiacetylene. In this work, the chromatic behavior of a poly(10,12-pentacosadiinoic acid)/titanium dioxide (TiO2) nanocomposite was studied. Infrared spectroscopy showed that above 55 °C the peak of the carboxyl groups undergoes a shift from 1690 cm−1 (25–55° C) to 1710 cm−1 (≥60 °C), which is reversible after cooling regardless of whether the sample was in the blue or red phase prior to heating. This indicates that the thermochromic behavior and the hydrogen bond shifting are not completely related, since the signal of the hydrogen bond is influenced by temperature, but is reversible; however, the color change is not. Importantly, TiO2 does favor thermochromic reversibility, unlike that indicated in previous reports. Computational chemistry showed that the effect of temperature on a polydiacetylene oligomer with three repeating units produces torsion, which directly impacts the strength of the hydrogen bonds between the carboxyl groups, coinciding with the experimental work.