The study under consideration represented the computational calculations of spectroscopic analysis of selected fluorescein dye named 7-Diethylamino-4-methylcoumarin (DEMC). Molecular Orbital (MO) calculations and the quantum mechanical calculations were studied in computational calculations. The MO calculations were done by using Hyper Chem program with semi-empirical AM1 and PM3 approximations. Quantum mechanical calculations were done by using Gaussian 09W. UV-Visible emission and absorption spectra included the relative energies ionization potential, infrared spectrum, and UV-Visible spectra. Calculations of solvents of low to high relative permittivity using molecular orbitals methods were studied for absorption spectra. The computed geometry of fluorescein dye was compared with those found experimentally/MP2 in gas phase. Solvatochromic study was done to check the effects of hydrogen bonding for the solvents. All the calculated results were compared with the available experimental data. HOMO-LUMO energy and MESP studies were also carried out to find the energy gap in gas and different solvents. Detailed comparison of Dye was evaluated in solvents to find the properties of dye for its useful applications. Absorption spectra were observed at 351 nm for water and acetone at 338 nm. HOMO and LUMO energy gap found for gas phase, water and acetone was -6.9816, -2.4386, and -6.5726 respectively. Following the obtained results, it was observed that dye has good interaction with acetone for its fluorescent use.

Keywords: Molecular orbital, DFT, Gaussian 09W, Spectroscopic properties, Fluorescein dye