Thin films of Indeno [1, 2-b] flourene-6,12-dione (I[1, 2-b]F dione) were performed by the thermal vacuum
evaporation technique. The identifications of a thin film such as structure, molecular structure and surface morphological were determined before and after annealing temperature using Fourier-transform infrared (FTIR), X-Ray diffreaction (XRD) and Scan electron microscopy (SEM). FTIR spectrum showed a diminishing of C═O bonds after annealing treatment. The analysis of XRD clarified that I[1, 2-b]F dione in its powder form is orthorhombic with space group P222. On the other hand, the as-deposited thin films were realized by amorphous nature, while the annealed I[1, 2-b]F dione thin films showed polycrystalline nature. The calculation of the average crystallite sizes proved that the annealed I[1, 2-b]F dione thin films were characterized by their nanostructure property. The SEM images illustrated that the aggregation of the particles has the formation of the nano-rod shape associated with average width in the range of 120–150 nm for the as-deposited thin film, while the average width of the branched nano-rod shape for the annealed thin films was observed to be in the range of 150–200 nm. The transmittance and reflectance spectrum at normal incidence of light in the range 190–2500 nm were employed to discuss the optical properties of as-deposited and the annealed I[1, 2-b]F dione thin films. Our conceptions elucidated that the optical transition type of I[1, 2-b]F dione films is the indirect allowed transition. The values of the fundamental energy gap for the as-deposited and the annealed films at 473 K were calculated out be 3.41 and 3.70 eV respectively. The dispersion of the refractive index was studied according to the single oscillator model. Moreover, the third-order nonlinear susceptibility and the nonlinear refractive index for I[1, 2- b]F dione thin films were calculated.