## 3 Results and Discussion
### Calculated vs. Experimental: The Explanation of Electrochemical Behavior
Good correlation between the experimentally and theoretically obtained spectra was achieved, showing that the share of protonated forms decreased with an increase in pH value. Moreover, HOMO-LUMO energies calculated for protonated form **A** and deprotonated form **D** and their distribution are presented in Figures S6 and S7 (Supplementary Materials) and Table S6 for compounds **5**-**9** in their favorable tautomeric forms. As seen in Figure 4, among studied pyridones **5**-**9**, \(N\)-unsubstituted pyridine containing an amido group in position 3 of the ring (**8**) had the lowest value of peak potential in both pH values (0.7 V and 0.6 V for pH values of 1.81 and 9.94, respectively), as well as the highest peak current in an acidic medium (31.3 \(\mu\)A cm\({}^{-2}\)). A strong correlation was found between the experimental potential values (Figure S7, Supplementary Materials) and the calculated energies (VIE, AIE, \(\Delta\)IE, Tables S2-S4) of **A** forms of molecules using both calculation methods (M06-2X and B3 LYP) in water, whereas the obtained correlation coefficient in gas phase was significantly lower. As for method M06-2X, a higher correlation coefficient was obtained for AIE values (\(R^{2}\) = 0.948), than for VIE values (\(R^{2}\) = 0.933), while as for the B3 LYP method, a better correlation was obtained for VIE values (\(R^{2}\) = 0.948) (Figure S8, Supplementary Materials). Bearing in mind the above, although groups in position 3 of the pyridone ring did not directly participate in electrooxidation, they indirectly stabilized the radicals formed through their electron-accepting ability. The highest current values obtained for **8** at pH 1.81 (Figure 4a) were in accordance with the lowest energy values of 7.78 and 7.53 eV for AIE and VIE, respectively. This could be related to the lower capability of the amido group to withdraw electrons, whereas radicals were more easily formed when compared to 3-cyano (**5**, **6** and **7**) and 3-pyridinium (**9**) analogues. On the other hand, the positive charge of molecule **9** made radical formation more challenging, which was reflected in the highest potential value (0.87 V). The highest peak current value of 48 mA cm\({}^{-2}\) obtained for **5** at pH 9.94 (Figure 4b) could be related to the stronger electron-withdrawing capability of the cyano group [40] which enabled the formation of deprotonated form **D** more easily with respect to **the** other 3-substituted pyridones. The correlation coefficients of AIE and VIE (**D** form) with peak potential values in an alkaline medium were significantly lower than those obtained for protonated forms of the compounds. The obtained results were expected, considering the fact that, in the solution at pH value of 9.98, the mixture of forms **A** and **D** was present. On the other hand, SWVs indicated that all molecules were more electrochemically active in an alkaline medium, evidenced by higher current values as well as peak potentials shifts towards less positive values. This could be ascribed to the negative charge present in deprotonated molecules. Furthermore, the emergence of a second peak in SWVs of **6** and **7** could be ascribed to the oxidation of the \(N\)-substituted chain [35]. Figure 7 depicts electron density distribution in the formed radicals obtained for the protonated form, **A**, and the deprotonated form, **D**, of compounds **5**-**9**. As seen in Figure 7, radicals of the deprotonated forms were stabilized throughout the whole molecule by delocalization, while electron densities of radicals derived from form **A** were localized on an atom or an atomic group. This could be explained by the fact that the C5 atom of protonated form **A** was \(sp^{3}\) hybridized, which prevented effective delocalization. On the other hand,  
in deprotononated form **D**, all carbon atoms were \(sp^{2}\) hybridized, enabling delocalization throughout the whole molecule.