In contrast with DMAC-TRZ, the ground-state optimized geometry of DMAC-py-TRZ has a bent structure (Figure ), as also observed in the crystal structure (Figure ). To better understand the structural differences between DMAC-TRZ and DMAC-py-TRZ, a rigid dihedral angle scan of DMAC-py-TRZ starting from an analogous orthogonal conformation to that of DMAC-TRZ has been performed. The rigid scan leads to a qualitatively similar picture for the two compounds (Figure ), with relevant MOs and NTOs in Figures and, showing the HOMO and LUMO localized on the donor and acceptor moieties, respectively. The presence of the nitrogen atom in the pyridine bridge effectively increases the electron-withdrawing strength of the acceptor, resulting in a stabilized LUMO and a smaller HOMO-LUMO gap in DMAC-py-TRZ (EHOMO -LUMO = 4.78 eV for the orthogonal structure) vs DMAC-TRZ (EHOMO -LUMO = 4.99 eV for the orthogonal structure). Accordingly, the S1 and T1 excitations occur at lower energy in DMAC-py-TRZ than in DMAC-TRZ and both the S1 and T1 states are stabilized compared to those of and). The rigid energy scan, however, points to a large increase of the ground-state energy when the dihedral angle deviates significantly from orthogonality, so that non-orthogonal conformations are hardly accessible. To address the bent conformer, we performed a relaxed scan of the dihedral angle, relevant results being shown in Figure . The relaxed scans show that for each of the emitters, two minima are present, corresponding to the orthogonal and bent structures. For DMAC-TRZ, the energy difference between the two conformers amounts to 0.04 eV, slightly larger than thermal energy at room temperature. The energy barrier for the interconversion between the two conformers, 0.22 eV (21.2 kcal/mol), is, however, much larger than thermal energy so that only the orthogonal geometry is expected to be significantly populated at room temperature. The situation is very different for DMAC-py-TRZ where the bent conformer (dihedral angle ~10 o ) is lower in energy than the orthogonal conformer by 0.20 eV and the energy barrier for the interconversion between the bent and orthogonal conformers is 0.20 eV (19.3 kcal/mol). Thus, at room temperature only the bent conformer is populated. The MOs and NTOs calculated for the bent structure (Figures and)