Liquid benzothiadiazole-based organic luminophores emitting light from the blue to red spectral region: synthesis, properties, and application in liquid scintillators

Liquid organic luminophores (LOLs) have been actively investigated as a new generation of functional materials in various fields of organic optoelectronics and photonics. However, many issues, including the structure-properties relationships and the development of LOLs emitting light in the red spectral range, remain poorly investigated. Here we report on the synthesis and investigation of a series of novel conjugated luminescent molecules consisting of a central 2,1,3-benzothiadiazole electron-withdrawing unit and lateral thiophene or phenylene electron-donating fragments with terminal trialkylsilyl units as solubilizing groups (SGs). Thermal and thermo-oxidative stability, phase behavior, structural properties, rheology, and optical and electrochemical properties of the obtained luminophores were studied and compared to their counterparts without SGs or with ineffective SGs for liquefaction. The target compounds are luminescent liquids with low glass transition temperatures (up to -65 degrees C) and viscosities (up to 1.7 Pa s) or liquid crystal materials emitting light in almost the entire visible spectral range with high photoluminescence quantum yield (PLQY) both in solutions (up to 97 %) and films (up to 87 %). For the first time, the application of LOLs as a new generation of organic liquid scintillators was demonstrated, achieving a light yield up to 1.7 times higher than that of a standard liquid scintillator.