Stimuli-Responsive Naphthalene Diimide-Based Charge-Transfer Liquid Materials Showing Thermal Response to Tune Photoluminescent Properties

Abstract

Stimuli-responsive luminescent liquid materials have recently attracted considerable attention due to their potential to address the limitations of solid-state materials, such as the necessity of organic solvents and the difficulty in fabricating composite systems. Liquid-state materials offer superior processability and enable facile modulation of photophysical properties by simply selecting appropriate solutes. In particular, molecular designs incorporating electron-donating or electron-accepting properties into liquid materials allow to form charge-transfer (CT) complexes upon dissolving solutes with their opposite electronic properties, altering both solution color and photoluminescence (PL) behavior. In this study, we developed a room-temperature supercooled liquid material based on an electron-accepting naphthalene diimide (NADI) derivative, BR-Val-NADI. Upon dissolving electron-rich naphthalene-based derivatives (NA-##s) into BR-Val-NADI, NA-##/BR-Val-NADI with CT character were readily obtained as solutions, exhibiting various colors and PL properties. NA-##/BR-Val-NADI also functioned as printable PL inks that could be applied onto various substrates such as glass and paper. Notably, the PL properties of NA-##/BR-Val-NADI were responsive to thermal stimuli, with temperature-induced changes in PL color and PL off/on switching. These results highlight the potential of NA-##/BR-Val-NADI as a new class of stimuli-responsive soft materials for applications in printable photonic devices and smart sensing platforms.

Keywords

naphthalene diimide / stimuli response / liquid material / stimuli-responsive liquid / photoluminescence

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