Deciphering the environment-dependent multicolor emission mechanism of phosphine amine PBT

Single-component multicolor luminescence is vital for advanced optical materials, yet its mechanism remains challenging to rationalize due to multiple environmentally regulated excited-state processes. In this Letter, the multicolor emission mechanism of PBT was elucidated using photophysical measurements and quantum chemical calculations. Specifically, in the solid state, intersystem crossing from S₁ and S₂ states to adjacent triplet states enables dual emission, with fluorescence and room-temperature phosphorescence together nearly spanning the visible region and showing clear excitation-wavelength dependence. In low-polarity solvents, phosphorescence is weakened, whereas in polar solvents it is suppressed and fluorescence dominates. We further demonstrate that excited-state intramolecular proton transfer is accessible in both the solid state and solution but does not directly contribute to emission. Twisted intramolecular charge transfer is also inhibited in solution by a high twisting barrier. This work clarifies the excited-state origin of PBT emission and guides the design of single-component multicolor and white-light emitters.