The absorption profiles of DABNA-1, tDABNA, CzBN and DtBuCzB in THF are all similar but the tert-butyl-substituted analogues have a more intense and red-shifted low-energy SRCT band and the SRCT band of the carbazole analogues is red-shifted compared to the DPA-based compounds due to an enhanced conjugation in the former (Figure , Table ). Importantly, each of these compounds has a low energy absorption band that is significantly more intense than commonly used iridium photocatalysts. For example, the e for SRCT bands in THF of In THF, DABNA-1, tDABNA, CzBN and DtBuCzB emit at λPL of 453, 458, 475, 483 nm (Figure ), emissions that are blue-shifted compared to that of 4CzIPN at λPL = 528 nm (Figure ). Acquisition of the emission profiles in different solvents confirmed the small degree of positive solvatochromism (Figure ). This implies that the singlet optical gap E0,0 for all four compounds remains broadly the same across the four solvents (Figures ). The largest variance in E0,0 was observed for tDABNA of 0.04 eV (Table ). In contrast, the emission of 4CzIPN undergoes more significant stabilization in polar media, reflected in the The singlet and triplet excited-state energies were measured in 2-MeTHF glass at 77 K (Figure and Table ). The S1 energy was inferred from the onset of the steady-state emission while the T1 energy was determined from the time-gated emission (acquisition 1-9 ms after excitation We next assess the photostability of the four compounds in each of the solvents by comparing their absorption spectra before and after photoexcitation using a 440 nm LED (Figure ). The absorption spectra of all four compounds in MeCN remained broadly unchanged. In THF, the diphenylamine-based emitters DABNA-1 and tDABNA were found to be photostable, showing no obvious changes in the absorption spectra (Figure and); however, the SRCT band in the absorption spectra of CzBN and DtBuCzB after irradiation is significantly blue-shifted (Figure and). Curiously the opposite phenomenon was observed in DCM where there is no appreciable change in the absorption spectra of CzBN and DtBuCzB, while the SRCT band in DABNA-1 and tDABNA is red-shifted. Considering the structural differences between DABNA-1 and tDABNA compared to CzBN and DtBuCzB, it is evident that the inclusion of diphenyl amine groups leads to an increased photostability in THF, while the structures with carbazole are more photostable in DCM.