The corresponding HOMO energy levels are -5.28, -5.25 and -5.31 eV, indicating that HOMO energy level TPPA-BQ is slightly more stabilized than the other two analogues. Although there is a visible subtle difference in measured HOMO levels between MeTPA-BQ and tBuTPA-BQ, DFT calculations predicted that they be the same. The electrochemical band gap was found to be 1.72, 1.70, and 1.73 eV for MeTPA-BQ, tBuTPA-BQ and TPPA-BQ, respectively. While the absolute values do not correlate with the DFT calculations, the distribution of HOMO-LUMO gaps is well modelled (Table ).