The as-prepared sample emits at 590 nm (FWHM = 106 nm), has a FPL of 3% and a tPL of 5.2 ns, while the ground sample emits at 755 nm (FWHM = 195 nm), has a much diminished FPL of 0.2% and a tPL of 1.8 ns. (Figure ). Akin to tBuTPA-BQ, the ground form of TPPA-BQ was stable under ambient conditions and the photophysics did not revert to the as-prepared form upon heating to 200 °C. However, the photophysics of the ground form could be converted to that of the as-prepared form upon fuming with EtOAc. Akin to the sublimed form of tBuTPA-BQ, the PXRD of TPPA-BQ showed a resolved diffraction peaks for the as-prepared sample, indicating its crystalline nature (Figure ). The diffractograms of the ground powder did not show any noticeable patterns indicating that these samples are in an amorphous state. The PXRD pattern is perfectly restored after EtOAc fuming of the ground sample of TPPA-BQ (Figure ). The asprepared sample of TPPA-BQ showed multiexponential emission decay kinetics with τP of 5.2 ns and average τd, of 60 µs. Variable temperature time-resolved PL measurements further confirmed the TADF behavior of as-prepared sample of TPPA-BQ (Figure ). However, when ground no TADF was observed, possibly due to its weak PL behavior. The 1 H NMR spectra of the ground samples dissolved in CDCl3 were the same as those of the as-prepared samples, indicating that grinding did not decompose the compounds, and that a solid-state transformation was responsible for the piezochromism. In the solid-state absorption spectra of TPPA-BQ, distinct differences were observed for as-prepared and ground samples (Figure ). The as-prepared sample showed absorption bands at ~310 nm, ~410 and ~475 nm. The ground sample has the same ~310 nm band but a new band at ~420 nm with a tail extending to 600 nm. Such a long wavelength tail likely indicates that partial conformational planarization results in the increase of conjugation to some extent in the ground form (Figure ). However, the absorption spectra of the sublimed and ground samples of tBuTPA-BQ are similar indicating that no significant changes occurred to its conformation. The grinding and fuming cycles for TPPA-BQ were repeated 20 times and showed a high degree of reproducibility, confirming the reversibility of the phase transformations and with no obvious fatigue response (Figure ). To demonstrate the practical application of TPPA-BQ as a photoluminescent ink, the compound was dispersed in EtOAc under ultrasonication for 2 min. The dispersed suspension was coated onto a filter paper by drop casting and left to dry for 1 h. A glass rod was used as the writing implements on the substrate (Figure ), and the areas of the filter paper upon which the rod was in contact showed a contrasting reddish color, indicative of the ground form while the rest of the filter paper emitted yellow-orange emission under UV light illumination. The distinct emission color change of the written text remained for at least 2 months of observation. The text could be erased upon the addition of EtOAc drops to the written region, while DCM, hexane and THF did not produce the same behavior. ).