Fluorescence Enhancement in a Tri(biphenyl-4-yl)amine Derivative via Solid-State Grinding with Metal Salts: Chemosensing and White Light-Emitting Diode Applications

Solid-state luminescent materials find enormous potential applications in LEDs, sensors, recognition, and imaging. On the other hand, molecular aggregations in the solid state limit their usage in real device applications. Herein, we report a 2-hydrazinopyridine derivative of tri(biphenyl-4-yl)amine (TBA-2HP) exhibited green fluorescence emission in the solid state and cyan in the solution. The aggregates present in the solid form of the TBA-2HP were disturbed by grinding solid powder with different metal salts, which enhanced fluorescence emission intensities. Herein, the surfaces of micron-sized metal salt crystal particles serve as templates for the TBA-2HP molecules, or in the broad sense, the salt crystal surfaces act as a “solid-state solvent.” The salt ground matrices exhibited varied emission intensities with metal salts like alkali, alkaline earth, and zinc metal salts. The gradual change in solid state emission color from yellowish green to cyan was observed in the ground matrices of zinc acetate salt with varied amounts of TBA-2HP. Furthermore, the electroluminescence properties of the TBA-2HP were investigated by fabricating the TBA-2HP-doped polymer on the surface of a near-ultraviolet (NUV) and blue light-emitting diode (LED). The TBA-2HP displayed green light emission upon coating a thin layer of TBA-2HP-doped polymer over the surface of a NUV LED bulb and white light emission upon coating a thin layer of TBA-2HP along with a red phosphor-doped polymer on the surface of a blue LED bulb. Moreover, the TBA-2HP was utilized to detect high-explosive picric acid in the solution.