LAUSR

Abstract Rhodamine B octadecylamine (RBO) lipophilic derivative is developed as a new thermochromic pigment in both solid and liquid system with temperature controlled turn-on fluorescence and visible color-transformation performances. In liquid system, RBO exhibits color-transformation from light pink to rose red under illuminant D65 and presents temperature controlled turn-on fluorescence, which is attributed to the atom transmitting to an upper level by the thermal excitation. The log Intensity T fits a linear relationship in the body temperature range of 37 °C to 45 °C. In solid system, RBO displays reversible thermochromic performances from pink to yellow under visible light and transforms from fluorescence pink to colorless under UV light, which is originated from the conjugation structure conversion of RBO by monitoring the structure changes during heating via FT-IR spectra. The thermochromic rate in the repeated heating-cooling cycles is fast, calculated to be 0.17 s−1 (heating) and 0.05 s-1 (cooling), respectively. The RBO possesses a good thermostability up to 380 °C. The solid system RBO can be made into a hand-writable thermochromic pen. The deposition of RBOS on paper is easily performed by manual drawing. The image drawn using the pink RBO pen is visible as a pink coating, and showing a pink-to-colorlessness color change on paper under visible light with temperature increase. This new rhodamine derivative with special thermochromic property of turn-on fluorescence and visible color-transformation performance can be applied in both solid and liquid systems, which is promised as a thermochromic coating to replace the intrusive measurement techniques and play a role in external/internal temperature measurements.