Kinetic and thermodynamic control of tetraphenylethene aggregation-induced emission behaviors: Nanoscience: Special Issue Dedicated to Professor Paul S. Weiss

Many aggregation-induced emission (AIE) systems exhibit broad and structureless luminescence emission spectra resembling the Gaussian distribution, which is likely due to kinetically locked molecular conformers in the condensed phase. To verify the hypothesis, a series of tetraphenylethene (TPE) derivatives are synthesized and characterized as aqueous nanoparticle suspensions. It is found that the unsubstituted TPE exhibits reduced fluorescence intensity accompanied by a blueshift of the emission maximum, after the temperature of the aqueous suspension is elevated and cooled to room temperature again. For a naphthalimide-substituted TPE compound, thermal treatment of the AIE aqueous suspension results in complete, irreversible aggregation-caused quenching (ACQ) of fluorescence, which can be restored by a redissolving-precipitation process of thermally treated aggregates. The phenomenon is ascribed as a relative population shift of a kinetic AIE (k-AIE) state to a thermodynamic AIE (t-AIE) or ACQ state, evidenced by differential scanning calorimetry, dynamic light scattering, and scanning electron microscopy. The phenomenon may be universal for many other AIE systems and could be explored as stimuli-responsive materials.