Unexpectedly, we observed that TPPQ showed photochromic behaviour in ethereal solvents. On exposure to UV light (365 nm) at room temperature in THF solution, over 6 minutes the blue band at 456 nm decreased in intensity while a broad, green band at 556 nm appeared, with a corresponding iso-emissive point at 504 nm (Figure ). At 77 K in glassy 2-MeTHF, there is no appearance of the green emission band and only the narrow blue emission band at 448 nm is observed (Figure ). There were no changes in the 1 H NMR spectrum of TPPQ in THF-d 8 before and after exposure to UV light (Figure ), which confirms that that there is no photodegradation of TPPQ. From these experiments, the appearance of the new green emission band at 556 nm in TPPQ is attributed to excimer formation. To corroborate these conclusions, we modelled a TPPQ dimer, which has a more stable S1 energy of 2.86 eV compared to the S1 energy of TPPQ monomer of 3.11 eV (Figure ). Both 4DMAC-TPPQ and 4PXZ-TPPQ also showed a similar but weak photochromic behaviour in ethereal solvents (Figure ). The photoluminescence quantum yield (FPL) in degassed toluene of 4DMAC-TPPQ is 13.7%, higher than those of TPPQ (2.1%) and 4PXZ-TPPQ (0.8%). Upon exposure to air, the FPL for TPPQ, 4DMAC-TPPQ and 4PXZ-TPPQ decrease to 1.9, 7.3, and 0.6%, respectively. The PL decays of the three emitters in toluene under degassed and aerated conditions are shown in Figure . There is only a single decay component observed for all three compounds, with lifetimes, tPL, of 7.9 ns for TPPQ, 20.2 ns for 4DMAC-TPPQ and 1.98 ns for 4PXZ-TPPQ.