Having the HOMO of chromium(iii) tris-(8-hydroxyquinolinate) mainly on metal 3d orbitals and the LUMO on the ligand leads to increased electrochemical stability.
Mono-/tri-β-substituted metalloporphyrins have been synthesized and characterized. Dramatic reduction in the HOMO–LUMO gap with tunable electronic, spectral and electrochemical redox potentials were observed as the number of electron withdrawing groups increased.