Thiophene Decoration Modulated Excimer Emission of Arylamine-Fluorene Luminophore for Visual and Ultrasensitive Physiological Temperature Sensing

Organic single-luminophore systems featuring regulated monomer–excimer emission constitute an attractive framework for adaptive photonic materials. Here, we report two thiophene-decorated fluorene derivatives, TDDF and MTDDF, designed to modulate molecular packing and excimer formation through heteroarene-involved interactions. Compared with the nonthiophene analogue DDF, thiophene incorporation decreases optical bandgaps, enhances thermal robustness, and promotes close intermolecular association, leading to pronounced excimer emission in aggregated states. Single-crystal analyses reveal that methyl substitution in MTDDF increases intermolecular spacing, enabling a finely tunable balance between monomeric and excimeric states. When dispersed in a fatty-acid phase-change matrix, MTDDF exhibits a distinct, reversible thermally modulated luminescence transition across the physiological temperature range, producing a continuous color shift from yellow-green to blue. This thermally driven packing reorganization enables highly sensitive ratiometric temperature readout, delivering a maximum sensitivity of 44% °C–1 near 37 °C, among the highest reported for organic luminescent thermometers. This work demonstrates thiophene decoration as an effective approach for stabilizing excimer states and provide a versatile design strategy for advanced thermoresponsive luminophores and stimuli-adaptive photonic materials.