Simple and general platform for highly adjustable thermochromic fluorescent materials and multi-feasible applications

Even though numerous thermochromic fluorescent materials (TFMs) have been reported, effective and universal strategies for the development of ideal TFMs with simple preparation, low cost, excellent performance and practicability are still urgently required. Herein, we report a simple and general platform for such TFMs via taking biomimetic lipid like fatty acids (FAs) as an effective matrix which is applicable to abundant simple fluorophores. Change of crystallinity of FAs induced by phase transition regulates the reversible interconversion between non-dispersion and dispersion states of fluorescent dyes (e.g., coumarins), thus leading to obvious fluorescence (FL) change of the TFMs based on both. The reaction mechanism was proved in detail by FL spectra, XRD and SEM techniques. The substituent effect of coumarins and the nature of FAs play important roles in adjusting the properties of the TFMs, such as FL colour and responsive temperature. Additionally, their multiple feasible potential applications (i.e., in situ thermometers, thermal response FL papers, FL colour change crayon, anti-counterfeiting and encryption, erasable or long-preservative thermal printing) with selective multi-mode (i.e., groove-fill, writable pen, loading on paper substrate) were developed. These TFMs with the merit of easy preparation, low cost, obvious colour change (ca. 100 nm shifts), fast response speed, good reversibility and high adjustability are very close to industrial application requirements. The design and preparation principles from this work should facilitate the development of other novel stimuli-responsive fluorescent materials.