Theoretical interpretation of electron delocalization potential of the substituent in o-hydroxynaphthalidene-p-substituted anilines for prospective molecular electronics applications

Abstract

The delocalization phenomenon plays a vital role in the electron transport properties of a molecule, which is essential for developing molecular-based electronics. The current work examined the delocalization potential of five theoretically designed low molecular weight anils, o-hyroxynaphthalidene-p-substitutedanilines(NP-X) with the substituent X(X = -CH3, -NO2, -OCH3, and –Cl) being placed in phenyl ring at the p- position to its functional moiety, azomethine linkage and compared with the compound without substitution(X = H). The geometric optimization through DFT with B3LYP/6-311G (d, p) level basis set indicated the anils to be coplanar. Theoretical FTIR could discriminate the aromatic and aliphatic C-H vibrational frequencies and confirm the vectorial flow of the electrons when the o-OH group and p-NO2 group were placed at the two extreme ends of anil, further supported by Natural Bond Orbital analysis. Atomic charge analysis indicated the significant effect on the charge of azomethine carbon atom. It followed the order: OCH3 < CH3 < H < Cl < NO2 parallel with the σp values of the corresponding substituent. The molecular electrostatic potential mapping identified azomethine nitrogen as an electron-rich centre. The global and local reactivity parameters indicated the highest tendency of NO2 substituted compound to accept electrons among the other compounds. The HOMO–LUMO energy gap of the NP-X predicted from Natural Localized Molecular Orbital analysis was found to be NP-H: 4.02 eV, NP-CH3: 3.94 eV, NP-NO2: 3.69 eV, NP-OCH3: 4.18 eV, NP-Cl: 4.10 eV. The overall studies corroborated the optimized delocalization in NP-NO2 with the lowest HUMO-LUMO gap, which would be better suited for developing molecular-based electronic devices than others. The importance of the electron delocalization phenomenon in searching for a molecular probe to develop molecular electronics device applications has been discussed.Graphical