The respective estimated LUMO energy levels are -3.56, -3.55 and -3.58 eV, following the trends predicted by DFT calculations that the LUMO energy level of TPPA-BQ is stabilized in comparison to MeTPA-BQ and tBuTPA-BQ (Table ). The oxidation potentials were also found to be reversible, with Eox of 0.94, 0.91 and 0.97 V for MeTPA-BQ, tBuTPA-BQ and TPPA-BQ, respectively, reflecting the relative donor strength of the substituted TPA (tert-butyl > Me > H).