Structure design of light-resistance fluorane dyes and preparation of color changing materials

Abstract

Fluorane dyes were widely applicated in the thermochromic area, especially in the form of smart textiles, as they could adjust color via electron transfer. However, developing perfect bright color and light-resistance fluorane dyes had remained challenging due to the intrinsic structural limitations. Here, we reported a series of new fluorane dyes with different electron withdrawing groups that controlled the electron cloud density of the lactone ring, which enhance the thermochromic stability and light-resistance properties. The red shift or blue shift of the absorption wavelength, which could broaden the dye's spectrum, was controlled by the number of electron-absorbing substituents. Moreover, fluorane dyes with a withdrawing group introduced at the R3 position of the lactone ring had excellent light-resistance ability, which was 66%∼57.2% lower than that of commercial dye after 14 h of light irradiation. But, the excess substituents would have weakened its original light-resistance. We also explain the photostability associated with the electron distributon using Density Functional Theory (DFT) simulation. This achievement in the development of light-resistance fluorane offers a promising solution for the application of color-changing materials with a broad absorption spectrum and light-resistance.