states and to understand at this lower level of theory the nature and the energies of the excited states. In addition, SOCME between S1/T1 states were determined at the optimized T1 state geometry to corelate the regiochemistry of the sulfur atoms with the magnitude of the SOC between these states. Similar to the geometry found in the X-ray crystal structures of tDPABT1B and tCzBT2B, the optimized S0 geometries of the four emitters are planar with respect to the DtBuCzB core, with the benzothiophene moieties slightly bent away from planarity (Figure ). Due to the rigid, fused structure of the four emitters, negligible geometrical change of the tert-butyl groups and benzothiophene moieties are observed between the S0/S1 geometries, reflected in the root mean squared displacement (RMSD) of around 0.044 Å and the small reorganization energies (λ) of around 0.11 eV (Figure ), similar to those seen for BTC-BNCz (0.062 Å and 0.12 eV, respectively, calculated at the M062X/6-31G* level). As the high frequency molecular vibrations contribute significantly to a larger FWHM in the emission spectra, the Huang-Rhys (HR) factors for the S1 state of the four emitters were calculated to quantify the coupling strength of the vibrational modes between S1 and S0 states. As shown in Figure , for each of the four emitters, the geometry relaxation is dominated by low frequency (<250 cm -1 ) twisting vibrational modes whereas the high frequency (> 2000 cm -1 ) vibrations are largely suppressed. These results align with the previously reported calculations of BTC-BNCz, suggesting that our four emitters should also exhibit narrowed emission.