Thermochromic Properties of Mixture Systems of Octadecylphosphonic Acid and Fluoran Dye

Abstract

We have examined the thermochromic behavior of thin films formed by mixing a fluoran dye (FD: 2 ′ -( o -chloroanilino)-6 ′ -di- n -butylaminospiro[isobenzofuran-1(3 H ),9 ′ -[9 H ]xanthene]-3-one) and octadecylphosphonic acid (P18). The coloring and discoloring states were revealed to be controllable by changing the rate of cooling from the colored mixture liquid ( 100°C); quenching at 0°C maintained the solidified colored state, yet discoloring occurred after slow cooling at the rate of 4°C/min. We confirmed by X-ray diffraction and FT-IR spectra that the solidified colored state is produced by formation of the supramolecules, in which seven molecules of P18 and one molecule of FD combined, whose aggregates are in a lamellar structure. In the discoloring state, the supramolecule is decomposed to P18 and FD due to the fractional crystallization of P18.