Thermodynamic Fluorescence Behavior of a Fluorenone Derivative through Solvent‐ and Temperature‐Controlled Hydrogen Bonding

Abstract A fluorenone derivative with an extended conjugated structure emitting visible light was examined as a functional fluorescent dye that responds to solvent and heat stimuli in a precisely controlled manner. Intermolecular hydrogen bonds between the fluorenone dye and solvent, which cause fluorescence (FL) quenching due to vibronic coupling, were broken and regenerated by adjusting the hydrogen bond acidity and basicity of solvent mixtures in various combinations or by varying the temperature. The fluorenone dye exhibited a unique heat‐induced FL emission enhancement during heating and returned to the quenched state during cooling. Thus, this FL change was highly reversible and repeatable. Moreover, through thermodynamic consideration based on the spectroscopic analysis, the Gibbs energy change was calculated for each solvent mixture composition to predict the thermodynamic preference for FL enhancement.