Empirical Relationship between Chemical Structure and Redox Properties: Mathematical Expressions Connecting Structural Features to Energies of Frontier Orbitals and Redox Potentials for Organic Molecules

A set of mathematical expressions to predict redox potentials and frontier orbital energy levels for organic molecules as a function of structural features is proposed. This is achieved by using the principal component regression method on reduction potential (<i>E</i>_red), oxidation potential (<i>E</i>_ox), highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) values calculated using density functional theory (DFT) on a training set consisting of 77 547 molecules from PubChem database. The first set of expressions allows prediction of <i>E</i>_red, <i>E</i>_ox, HOMO, and LUMO values using molecular fingerprints alone with <i>R</i>² of ca. 0.74, 0.82, 0.92, and 0.85, respectively, which can be used for preliminary screening of molecules before performing DFT calculations. In the second set of expressions, when we include DFT-calculated HOMO and LUMO values as additional descriptors, the <i>R</i>² values of <i>E</i>_ox and <i>E</i>_red predictions increase to 0.91 and 0.90, respectively. This more accurate approach for redox potential predictions is still significantly more computationally efficient compared to DFT calculations of redox potentials. The potential of these approaches is demonstrated by using the examples of polyacenes and quinoxaline family of molecules. These empirical relations are ideally suited for high-throughput screening for a variety of optoelectronic applications. The resultant tool, QSROAR, is made available at https://github.com/piyushtagade/qsroar_version2