Tracing the transition from covalent to non-covalent functionalization of pyrene through C-, N-, and O-based ionic and radical substrates using quantum mechanical calculations.

Pyrene is one of the widely investigated aromatic hydrocarbons given its unique optical and electronic properties. Modulating inherent characteristics of pyrene covalent or non-covalent functionalization has been attractive for a wide variety of advanced biomedical and other device applications. In this study, we have reported the functionalization of pyrene C, N, and O based ionic and radical substrates, and emphasized the transition of covalent to non-covalent functionalization through making the modulation in the substrate. As expected, strong interactions were observed for cationic substrates, however, anionic substrates also exhibited a competitive binding strength. For instance, methyl and phenyl substituted CH complexes exhibited IEs in the range of -17 kcal mol to -127 kcal mol and -14 kcal mol to -95 kcal mol and for cationic and anionic substrates, respectively. The analysis of topological parameters showed that un-substituted cationic, anionic, and radical substrates interact with pyrene covalent interactions, and further become non-covalent upon methylation and phenylation of the substrates. In cationic complexes, the polarisation component is observed to be dominating the interactions, whereas highly competitive contributions from polarization and exchange components were observed in anionic and radical complexes. The contribution of the dispersion component increases with an increase in the degree of methylation and phenylation of the substrate, and starts dominating once the interactions become non-covalent in nature.