Single crystals suitable for X-ray diffraction of PTZ-TPI were obtained directly from temperature gradient sublimation (Figure ). The most notable feature found in the structure was that the PTZ adopts an axial conformation with an C9-N12-S19 angle of 111.68°. The PTZ shows a butterfly geometry, with the angles between its aromatic ring planes being 44.47°. TPI adopts a twisted conformation where the phenyl groups 1 and 5 being nearly orthogonal to the imidazole plane (83.62 and 89.79° between planes). By contrast, the phenyl groups 2 and 4 were found to be close to the same plane as the imidazole (18.88 Density Functional Theory (DFT) calculations at the PBE0/6-31G(d,p) level were performed to gain insight of the optoelectronic properties of the studied materials. The nature of the excited singlet and triplet states and their energies were determined from time-dependent density functional theory (TD-DFT) within the Tamm-Dancoff approximation (TDA) at the same level of theory. The TPI core adopts a geometry in the ground state where all four phenyl rings are twisted with respect to the plane of the imidazole: phenyl rings 1 and 5 are twisted by 68° and 51°, respectively, while phenyl groups 2 and 4 are twisted by 29° and 25°, respectively (Figure ). The dihedral angle between the phenylene bridge and the TPI core decreases by 6-7° in the donor-acceptor compounds, while the donor groups are themselves disposed in a close-to perpendicular orientation with respect to the bridge. DMAC was found to adopt the most twisted conformation, followed by PTZ and PXZ with torsion angles of 83°, 81°, and 71°, respectively. Such a high degree of twisting is expected to lead to only minimal conjugation between the donor and the rest of the The HOMOs of DMAC-TPI, PXZ-TPI, and PTZ-TPI are mostly localized over the DMAC, PXZ and PTZ, respectively, with a small portion of electron density residing on the phenylene spacer. TPI acts as the electron acceptor in these systems as the LUMOs were found to be delocalized throughout the imidazole core with all the adjascent phenylenes involved; phenyl group 4 contributes less to the electron density distribution of the LUMOs of these compounds than the other phenyl groups. The HOMO level of TPI is -5.45 eV (-5.46 eV , calculated using B3LYP functional). Introduction of the donors results in a destabilization of the HOMO by 9-42 meV. The relative HOMO levels of DMAC-TPI, PXZ-TPI, and PTZ-TPI at -5.28, -5.03 and -5.36 eV, respectively, reveal that in this family of compounds the donor strength increases from PTZ to DMAC to PXZ. The LUMO level of TPI is -0.76 eV, which classifies this moiety as a weak electron acceptor. We note that there is discrepancy with previously reported calculated LUMO value for TPI of -1.16 eV , however, this value was obtained using B3LYP functional, while we V in DCM , scan rate = 100 mV s -1 ).