Redox potentials of a molecule can be tailored by tuning its HOMO and LUMO energy levels. According to the molecular orbital theory, a lower LUMO level means higher electron affinity and thus a higher reduction potential for the molecule. Lowering the LUMO levels could be achieved in two ways; (i) substituting electron withdrawing groups to the redox active molecule and (ii) extending the conjugation in a molecule through aromatic rings.[4-5] Extending the conjugation is a conventional approach and could increase the electrochemical dead weight of the molecule, resulting in reduced theoretical capacity. Here we chose the first route and demonstrate a remarkable tunability in the discharge potential from 2.1 to 2.6 V vs. Na+/Na, with a sodium intake of ~1.6 ions per molecule, using various electrophilic substitutions on perylene diimides. Further, acknowledging the importance of a single plateau voltage profile in commercial rechargeable batteries, we attempt to achieve a single redox peak in PDIs by tuning certain parameters. With the understood inherent advantage of greater coordination energy, we presumed that the dianion species could shift the equilibrium just by having a naked state energy (energy before coordination) similar to that of the radical anion. The naked state energies of a perylene diimide derivative can be tuned by changing the dihedral angle in the ring. A single plateau discharge profile is obtained for tetra bromo substituted perylene diimide with dihedral angles of θ1 & θ2=38o. Detailed structural analysis and electrochemical studies on substituted PDIs unveil the correlation between molecular structure and voltage profile. The results are promising and offer new avenues to tailor the redox properties of organic electrodes, a step closer towards the realization of greener and sustainable electrochemical storage devices.
 Z. Song, H. Zhou, Energy & Environmental Science 2013, 6, 2280-2301.
 Y. Liang, Z. Tao, J. Chen, Advanced Energy Materials 2012, 2, 742-769.
 C. Huang, S. Barlow, S. R. Marder, The Journal of Organic Chemistry 2011, 76, 2386-2407.
 G. S. Vadehra, R. P. Maloney, M. A. Garcia-Garibay, B. Dunn, Chemistry of Materials 2014, 26, 7151-7157.
 Z. Song, H. Zhan, Y. Zhou, Angewandte Chemie International Edition 2010, 49, 8444-8448.