## 3 Results and Discussion
### Density Functional Theory (DFT) Calculations  
The DFT calculations (B3 LYP functional) with 6-311G++ basis set were used to obtain the optimized structure of the (Bar-CLA) complex. The minimum SCF energy after 54 optimization steps was found to be \(-2097.881963\) a.u (Figure S7). The optimized geometry of the (Bar-CLA) complex with the Mulliken atom-numbering scheme is shown in Figure 9. The optimized structure that shows the bond lengths of the (Bar-CLA) complex is represented in Figure 10.  
The bond lengths and bond angles are presented in Supplementary Tables S3 and S4. The Mulliken charges for (Bar-CLA) complex were also calculated and are represented in Supplementary Table S5. The molecular electrostatic potential (MEP) in connection to color grading can display charge distribution in 3D. The MEP makes it simple to determine the shape, size, chemical \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{2}{c}{**Energies in (kJ/mol)**} \\ \cline{2-3}  & **BarCS Complex** & **BarS Complex** \\ \hline Binding energy (Total) & \(-40.642\) \(\pm\) 4.324 & \(-31.089\) \(\pm\) 9.997 \\ Van der Waals energy (EvdW) & \(-83.954\) \(\pm\) 7.623 & \(-39.276\) \(\pm\) 11.001 \\ Electrostatic energy (Eelec) & \(-186.670\) \(\pm\) 4.302 & \(-288.981\) \(\pm\) 8.653 \\ Nonpolar solvation energy (Gononpolar) & \(-58.527\) \(\pm\) 3.121 & \(-31.801\) \(\pm\) 9.741 \\ Polar solvation energy (Gpolar) & \(288.509\) \(\pm\) 2.652 & \(328.969\) \(\pm\) 3.955 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Binding free energies (\(\pm\) standard deviations) from MM-PBSA calculations for BarCS complex and BarS complex. reactivity, and electrostatic potential of a substance. The strength of the electrostatic potentials of the (Bar-CLA) complex is represented through an MEP map (Figure 11). The MEP surface generated by DFT describes the nucleophilic or electrophilic properties. Electropositive regions are shown in blue and electronegative zones are shown in red (Figure 11). The red region, referred to as the nucleophilic area and susceptible to electrophilic attack, indicates the highest negative range for (Bar-CLA), which was \(-\)7.639 \(\times\) 10\({}^{-2}\) The maximum positive range, shown by a blue region and referred as an electrophilic area susceptible to nucleophilic attack, was +7.639 \(\times\) 10\({}^{-2}\) (Figure 11). These results show the preferential binding sites for electrophilic and nucleophilic regions on the molecule [54,55]. The MEP surface map revealed, by evaluating the data, that all hydrogen atoms had positive potential values and that N, O, and Cl atoms had negative potential values. Figure 10: Optimized structure of the (Bar-CLA) complex showing bond lengths. Figure 9: Optimized structure of the (Bar-CLA) complex with the Mulliken atom-numbering scheme. The experimental electronic absorption spectra of (Bar-CLA) exhibited an absorption band with \(\uplambda\)max at 520 nm [56]. By using the TD-DFT method in the gas phase, the nature of the electronic transitions was investigated (Figure S8). From TD-DFT calculations at 508 and 419 nm, two electronic absorption bands were produced (Figure S8). The first excited state (508 nm) was attributed to the HOMO to LUMO transition, whereas the second excited state (419 nm) was ascribed to the HOMO-1 to LUMO transition. The HOMO can be seen mainly in the CLA moiety of the (Bar-CLA) complex. The LUMO can be seen in the Bar moiety of the (Bar-CLA) complex [57]. The spatial arrangements of HOMO and LUMO, and the HOMO-LUMO gap, and associated energies are shown in Figure 12. The MO energy level diagram of the (Bar-CLA) is shown in Figure S9. Figure 11: MEP surface map of the (Bar–CLA) complex with respective color scales. The HOMO to LUMO and HOMO-1 to LUMO gaps (\(\Delta\)E) for (Bar-CLA) were observed to be 2.4406 and 2.9533 eV, respectively (Figure 12) [58]. Table S6 lists a few gas-phase molecular parameters according to HOMO-LUMO plot. The FTIR spectrum was explored by the DFT, B3 LYP/6-31 IG++ level of theory (Figure 13).