Color Change and Thermal Stability of Polydiacetylenes Containing Intermolecular and Intramolecular Hydrogen Bonds

Abstract

We investigated temperature dependence of the UV-vis and infrared absorption spectra of PDA with different alkyl chain lengths and methylene spacer lengths and containing carboxylic acid and amide groups capable of forming intermolecular and intramolecular hydrogen bonds in order to clarify their color change behavior upon heating. Intermolecular hydrogen bonds formed between PDA molecules via carboxylic acid dimers showed a stabilizing effect on PDA, and showed different thermal responses depending on the carbon number of the methylene spacer. On the other hand, it was found that PDA containing amide groups in the side chains, in which one-dimensional hydrogen bonds form along the conjugated main chain direction, showed poor thermal stability. We confirmed that PDA with both carboxylic acid and amide groups exhibited the most remarkable effect of thermal stabilization by intramolecular and intermolecular hydrogen bonds, and a reversible color change from blue to red phases in the temperature range below 130℃.