Substituent-Engineered Spirofluorene-Boron Emitters: Integrating TADF, Visible Afterglow, and Mechanochromism in a Single Material

A series of spirofluorene-triarylborane derivatives bearing tunable triarylamine donors (-H, -OMe, -SMe) were designed and synthesized to systematically investigate substituent effects on their photophysical behaviors. The methoxy-substituted compound ^<b>F</b><b>XylB-DOBPDA</b> exhibits efficient thermally activated delayed fluorescence (TADF), characterized by a small singlet-triplet energy gap (Δ<i>E</i>_ST) of 0.05 eV, along with notable aggregation-induced emission enhancement (AIEE). Remarkably, through a host-guest doping strategy using triphenylamine (TPA) as the matrix, the system displays clearly visible afterglow under ambient conditions. In particular, the ^<b>F</b><b>XylB-DOBPDA@TPA</b> codoped system achieves TADF-promoted long afterglow with lifetimes exceeding 100 ms. Additionally, reversible mechanochromic luminescence is observed, indicating multistimuli-responsive behavior. The combination of experimental analyses and theoretical calculations reveals that subtle changes in substituents critically influence intramolecular charge transfer and excited-state dynamics. These results offer valuable insights into molecular design strategies for achieving tunable emission in solid-state materials. With their integrated TADF, afterglow, and stimuli-responsive properties, these multifunctional materials demonstrate significant potential for applications in organic light-emitting diodes (OLEDs), mechanical sensors, anticounterfeiting labels, and optical storage technologies.