The efficient and accurate calculation of redox potentials of organic molecules is important for numerous applications ranging from developing organic photocatalysts and solar cells to understanding bioorganic and enzymatic reactions. State-of-the-art calculations of redox potentials utilizing linear free energy relationships correlating redox potentials with computed observables (e.g. orbital energies) have shown excellent results and reliable predictive models for a certain families of small organic molecules. This provides for a faster and simpler way to estimate the redox potentials of unknown molecules within the same family. However, constructed linear correlation of redox potentials against molecular orbital energies of large molecules such as porphyrins, phthalocyanines and phenazines have not been reported. This investigation focuses on testing different theoretical approaches including semi-empirical methods such as PM3 and AM1 as well as density functional method such as B3LYP. These theoretical methods have been employed in conjunction with several commonly used solvation models (SMD-PM3, SMD-AM1, SMD-B3LYP) and the 6-31G* basis set. This will allow us to computationally predict redox potentials for a large, diverse group of organic dyes by linearly correlating computed frontier orbital energies (HOMO-LUMO) with experimental redox potentials as measured in dichloromethane solvent. Our preliminary results utilizing 6- 31G* as a basis set showed that the inclusion of a solvent model on the structural geometry optimization is imperative to obtain a correlation coefficient (R2) greater than 0.9 and a mean absolute deviation value less than 0.07 V. The correlations obtained can be used to predict redox potentials of new molecules.

Estimating the redox potentials of organic dyes in dichloromethane

253rd National Meeting (2017)

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