Boron Ketoimine Fluorophores with Unique Optical Properties: Multicolor Tuning, Efficient Dual-State Emission, and Reversible Acid-Base Response

Organic luminophores with high emission efficiency in solution as well as solid-state have received increasing attention due to their promising applications in biosensors, biological imaging, and optoelectronic devices. Herein, four triphenylamine (TPA)-substituted boron ketoimine molecules (TPA-BKI a-d) are designed and synthesized by combining a donor-acceptor (D-A) electronic system and highly twisted block. The asymmetry of molecular and the planarity of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) sides in the excited state endow TPA-BKI a-d with rigidified conformations, allowing bright emission in dilute solution. Additionally, their highly twisted structures avoid close contact between molecules and detrimental exciton interactions, leading to efficient emission in the solid state. Meanwhile, the emission colors are modulated by the incorporation of different substituents through the amino-yne click reaction. Furthermore, because of the protonation and deprotonation of the amino substituents, TPA-BKI-d exhibits reversible alterations of optical properties in both solution and solid states.