Anti-Kasha's rule in phenothiazine derivatives and metal–organic frameworks: mechanism investigation and application in hypochlorite detection

Abstract

In recent years, some organic molecules have been found to produce luminescence that does not obey Kasha's rule in the aggregate state. This luminescence often originates from upper and the lowest energy-excited states. However, developing more single-component compounds with anti-Kasha's rule emissions and expanding their applications remains challenging. Herein, two phenothiazine derivatives are found to have anti-Kasha's rule luminescence in the aggregate state. Studies on photophysical properties, single-crystal structures, femtosecond transient absorption (fs-TA), and theoretical calculations indicate that the restriction of intramolecular motions (RIM) is the mechanism for the multiwavelength emission. Furthermore, a new luminescent Cd MOF, Cd-PTZ-db, which inherits the luminescence and structural characteristics of the phenothiazine derivative ligand, demonstrates great potential in the detection of hypochlorite (ClO⁻). This work gains a deeper understanding of the effect of RIM on luminescence in the aggregated state, and once again proves that the rigid structures of MOFs can work as the foundation for developing advanced solid-state emissive materials and other practical applications.