Structural and Electronic Characterization of Two Indole-Derived Schiff Bases: A Combined Experimental and DFT Study

This study investigates the synthesis and characterization of indole derivatives (C17H15N3O) and C17H14BrN3O employing the Density Functional Theory. Experimental characterization using both Infrared and Ultraviolet-Visible techniques was done on synthesized compounds resulting from the formation of hydrazones and yielding information on functional groups, electronic transitions, and structural characteristics. DFT/B3LYP calculations using both (STO-3G*) and (3-21G) basis sets were used for the molecular geometry optimization, Mulliken charge distribution, vibrational spectral simulations, and orbital energies. From the comparison of the two basis sets, it was indicated that the (3-21G) can produce results closer to the experimental results, especially for bond length, vibrational frequency, and electronic transitions. Accordingly, the combined use of both methods provides for the assignment of structural parameters with the utmost precision, charge distribution interpretations with utmost reliability, and a better understanding of molecular stability. This combined approach further emphasizes the role played in computational chemistry to supplement and establish spectroscopic observations of systems made of heterocycles such as indole derivatives. We observe good agreement between the theoretical and experimental results regarding the structural and electronic properties, where ( UV-Vis absorption spectrum (Theo) (DFT/B3LYP, STO-3G*-268.95 nm, 3-21G -282.92 nm, expt -282 nm) for the first compound and ((Theo)(DFT/B3LYP, STO-3G*-286.85nm, 3-21G -289.24 nm,expt -288 nm)) for the second compound.