Ground- and Excited-State Dipole Moments of 1, 2-Diazine Nanomaterials Using Solvatochromic Method

The ground-state \( (\mu_{\text{g}} ) \) and excited-state \( (\mu_{\text{e}} ) \) dipole moments of three 1, 2-diazine nanomaterials (pyrrolo-pyridazine derivatives) were determined using the solvatochromic shift methods, i.e. Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt equations. All these equations are based on the variation of Stokes shift with solvent’s dielectric constant and refractive index. Theoretical \( \mu_{\text{g}} \) values were also evaluated by quantum chemical calculations using the DFT method by adopting B3LYP/6-31G* level of theory (Gaussian 03). It was observed that all the three 1, 2-diazine nanomaterials possess higher dipole moment values in the excited singlet-state than in the ground-state. This confirms that the excited state of these nanomaterials is more polar than the ground state. Therefore, the solvent–solute interactions should be stronger in the excited singlet-state than in the ground-state, demonstrating an important redistribution of charge densities between both electronic states.