Effect of Solvent Polarity on the Absorption and Fluorescence Spectra of Nicotinamide: Determination of Ground and Excited State Dipole Moments

Abstract

Nicotinamide (NIC) is an amide-form vitamin with a carboxamide group at b positions that is involved in a variety of biological activities. The drugs contain functional groups which control the type and degree of interaction with different solvents. In this research, the ground and excited state dipole moments of nicotinamide (NIC) were estimated using solvatochromic effects and computational work. A general overview of solvent effects on the electronic absorption and fluorescence spectra of NIC is presented. In both spectra, pronounced solvatochromic effects were observed, and the shift of emission peaks was larger than the corresponding absorption spectra. The experimental ground state ( μg ) and excited state (μe) dipole moments of NIC are estimated from solvatochromic shifts of absorption and fluorescence spectra. The differences between the excited and ground state dipole moments determined by all the methods are quite similar. The HOMO-LUMO energy band gaps were calculated and found to be 5.566 eV. The excited state dipole moment is found to be higher than those of the ground state for all of the used methods, and it is attributed to the more polar excited state of NIC. Finally, the observed spectral properties, measured values of dipole moments, and electronic structures of NIC in different solvents provide important details about charge distribution and solute-solvent interactions that may be helpful in the investigation of these molecules in biological systems.