(354 nm, e=4.1×10 4 M -1 cm -1 )], which are attributed to LE π-π* transitions of both the donors and acceptor moieties based on a comparison with literature data of BP and GCz. Weaker and broader absorption bands are observed at 460 nm (e=1.6×10 4 M -1 cm -1 ) for 2GCzBP, 506 nm (e=0.7×10 4 M -1 cm -1 ) for 2DPACzBP, 436 nm (e=1.4×10 4 M -1 cm -1 ) for 2FBP2GCz and 464 nm (e=1.1×10 4 M -1 cm -1 ) for 2FBP2DPACz, which are assigned to ICT transitions from the donor units to the acceptor core, assignments that are corroborated by the relative oscillator strengths (f = 0.04, 0.01, 0.10 and 0.04 for 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz, respectively) calculated by TDA-DFT (Figure The prompt fluorescence and phosphorescence spectra in 2-MeTHF glass at 77 K were measured to determine the S1 and T1 energies from their respective onsets (Figure ). The S1 energies of 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz are 2.45, 2.12, 2.56, and 2.34 eV, and the T1 energies are 2.25, 2.12, 2.33, and 2.33 eV, respectively. The observed trends for both S1 and T1 energy levels align with the computational data presented in Figure . The phosphorescence spectra of 2GCzBP and 2FBP2GCz are structured, and each is assigned from TDA-DFT calculations as a mixed locally excited triplet ( 3 LE) state of the acceptor (BP-F) and charge-transfer ( 3 CT) state (Figure ). The ΔEST of 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz are 0.20, 0.00, 0.23, and 0.01 eV, respectively, which are similar to the trend in the calculated values, where 2FBP2GCz has the largest calculated ΔEST of 0.10 eV compared to 2GCzBP (0.04 eV), 2DPACzBP (0.08 eV) and 2FBP2DPACz (0.04 eV), as shown in Figure .