The powder form of the new indole derivative 4-(((3-chloro-1H-indol-2-yl) methylene) amino) phenol [Indol-
4Ap] was synthesized and subsequently converted to a thin film [Indol-4Ap]TF using the Sol-Gel spin coating
technique. Numerous characterization techniques, including Fourier transform infrared (FTIR), nuclear magnetic
resonance (NMR), X-ray diffraction (XRD), and ultraviolet–visible (UV–Vis) optical spectroscopy were used to
characterize [Indol-4Ap]TF. Additionally, using density functional theory (DFT), optimization tvia TD-DFTD/
Mol3 and Cambridge Serial Total Energy Bundle (TD-FDT/CASTEP) was developed. The DFT calculations
accurately matched the observed NMR and FTIR spectra and validated the molecular structure of the examined
materials. The average crystallite size of [Indol-4Ap]TF, as determined by XRD calculations, is 12.02 nm. The
optical properties of the films were determined using optical absorbance spectrophotometric measurements in
the 200–800 nm wavelength range. The optical energy bandgaps computed using Tauc’s equation for the [Indol-
4Ap]TF are 3.152 and 2.751 eV, respectively. Whereas the [Indol-4Ap]iso has a bandgap of 3.074 eV as determined
by TD-DFT/DMol3. The optical characteristics predicted by CASTEP in TD-DFT are in excellent agreement
with the experimental values. The investigated