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

## TL;DR

This paper studies how substituents affect the properties of 9-fluorenone, revealing insights into their electronic and optical behaviors for potential use in organic electronics.

## Contribution

The study introduces a comprehensive analysis of substituent effects on 9-fluorenone using advanced computational methods and various electronic and optical property evaluations.

## Key findings

- Electron-donating and electron-withdrawing substituents significantly alter the electronic and optical properties of 9-fluorenone.
- 2-nitro-9-fluorenone shows enhanced charge transfer and higher polarizability and nonlinear optical properties.
- Hirshfeld surface and crystal packing analyses reveal structural insights into substituent effects.

## Abstract

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.