Effects of Substituents on 9-Fluorenone: Spectroscopic, Hirshfeld, Optical, NLO, IFCT, and CTM Properties

The effect of substituent groups on 9-fluorenone derivatives was investigated using density functional theory (DFT) and the Multi-Objective Wave Function Analyzer for Chemists. 9-Fluorenone derivatives, substituted at the 2-position, were studied in terms of their structural, electronic, and optical properties. The effects of electron-donating and electron-withdrawing groups were investigated through FTIR and 1H NMR spectra, and the absorption and emission spectra were determined to identify electronic transitions and optical properties. For the electronic properties of the studied molecules, HOMO–LUMO molecular orbital analyses were performed, and average local ionization energy (ALIE) and electrostatic potential (ESP) surface analyses were conducted to determine the reactive regions of the molecules. Additionally, electron density-based analyses such as ELF, CTM, LOL, IFCT, and LOLIPOP were also carried out. The effect of substituent groups at the 2-position of 9-fluorenone on the dipole moment, polarizability, and nonlinear optical (NLO) properties was evaluated, and it was found that the 2-nitro-9-fluorenone molecule exhibited higher charge transfer. Harmonic Oscillator Model of Aromaticity (HOMA) index was determined to assess aromaticity. Finally, crystal packing and Hirshfeld surfaces were determined. The results suggest that the studied 9-fluorenone derivatives, with their electronic polarization, emission, absorption and nonlinear optical (NLO) properties, are potential candidates for applications such as organic field-effect transistors (OFET), liquid crystals, optical brighteners, organic photovoltaics (OPV), organic light-emitting diodes (OLED) and similar applications, and that other derivatives may also be developed.