Steady-state absorption and photoluminescence (PL) spectra of dBr-tBu-DiKTa and tBr-DiKTa in different solvents are shown in Figure . Both absorption and PL spectra undergo a small bathochromic shift (120-150 meV) with increasing solvent polarity, a phenomenon consistent with short-range charge transfer (SRCT) character of the emissive excited states in MR-TADF materials. In toluene (PhMe) solution, the lowest energy absorption maximum of dBr-tBu-DiKTa is centred at 445 nm and the main PL peak, lPL, is at 464 nm.