The dihedral angles between the donor and acceptor moieties were found to be around 87. The S1 energies are 2.04, 1.95, and 1.99 eV for DMACPyBP, PXZPyBP, and DPACzPyBP, respectively, while the T1 energies decrease from 2.00 to 1.78 and 1.84 eV, respectively, following a trend consistent with the decreasing DEHOMO-LUMO across the series. The clear spatial separation of the frontier orbitals in all three compounds results in a small ΔEST of less than 0.17 eV. Natural transition orbital (NTO) analyses of S1 and T1 excited states were modelled at the S0 geometry (Figure . 2b), revealing that the S1 state in each compound exhibits a clear intramolecular charge transfer (CT) character, while the T1 state has a mixed locally excited (LE) and CT character.