A Conformation-Dependent AIE-TADF Fluorophor Based on a Phenothiazine-Diphenyl Sulfone Derivative for Tumor Cell Growth Monitoring

An organic compound composed of a phenothiazine (PTZ) electron donor moiety and 4-fluoro diphenyl sulfone (FDPS) electron acceptor unit, PTZ-FDPS, which exhibited simultaneously polymorphism, aggregation-induced emission, thermally activated delayed fluorescence (TADF), and mechanochromic luminescence (MCL), was reported. PTZ-FDPS formed two different aggregates: rod-like crystal (C1) and block crystal (C2). Crystallographic results indicated that C1 and C2 belonged to a quasi-equatorial conformer and a quasi-axial conformer, respectively. Due to the transformation of molecular conformation under external force, C2 exhibited significant MCL performance compared with C1. More intriguingly, the fluorescence of PTZ-FDPS nanoparticles (NPs) exhibited a clear responsiveness to the tumor cell microenvironment. Initially, the NPs emitted predominantly green fluorescence, corresponding to a quasi-equatorial conformation. However, upon cellular uptake, their fluorescence shifted to a blue-green dual emission, indicating a conformational transition from quasi-equatorial to quasi-axial. As the tumor cells grew, the fluorescence gradually reverted from blue-green dual emission back to green, suggesting a return of the molecular conformation from quasi-axial to quasi-equatorial. This study offers a valuable strategy for the design and application of multifunctional materials.