Determination of Ground- and Excited-State Dipole Moments of Pyronin B Using the Solvatochromic Method and Quantum-Chemical Calculations

Ground- and excited-state dipole moments of pyronin B (PyB) in n-alcohols (methanol to n-hexanol), acetonitrile and acetonitrile-benzene solvent mixtures with different polarity were determined using the solvatochromic method and quantum-chemical calculations. The ground-state dipole moments were calculated using both the experimental Guggenheim-Smith method (GSM) and the theoretical (SCF MO LCAO) in CNDO/2 and MNDO methods. The values of the theoretical dipole moments of PyB were determined to be 11.29 and 3.43 D (Debye) for the CNDO/2 and MNDO methods, respectively. Experimental ground-state dipole moments for PyB increased from 3.13 to 13.77 D in n-alcohols, and 9.25 to 14.63 in AN and AN-BN solvent mixtures, with decreasing polarity. The excited-state dipole moment values were determined from Lippert's and Bakhshiev's equations. The ground-state dipole moments were found to be higher than the excited-state moments. It was determined that the groundstate structure was more polar and stable as compared to the excited-state