Steady state absorption and fluorescence study: Estimation of ground and excited state dipole moments of newly synthesized pyridazin-3(2H)-one derivatives

Steady state absorption and emission spectra of newly synthesised pyridazin-3(2H)-one derivatives 5-(2-hydoxy-4-methyl-phenyl)-2-phenyl-2H-pyridazin-3-one [HMP], 5-(5-bromo-2-hydroxy-phenyl)-2-phenyl-2H-pyridazin-3-one [BHP] and 5-(4-chloro-2-hydoxy-phenyl)-2-phenyl-2H-pyridazin-3-one [CHP] were studied in different solvents in order to estimate the ground and excited state dipole moments. Ground state dipole moments (μg) were estimated using the theoretical method provided by Gaussian-09 program and experimental method suggested by Guggenheim. Ground state dipole moments measured from theoretical and experimental methods for the molecule CHP only are quite close to each other. Thus, molecular geometry taken for this molecule CHP under theoretical and experimental methods may correlate well. Excited state dipole moments (μe ) of all the three molecules were estimated using solvatochromic shift method. From the results of the effect of solvents on emission spectra it may be inferred that in HMP and BHP molecules there exists π → π⁎ transitions and in CHP molecule there exists n → π⁎ transition. Under solvatochromic shift method, three equations proposed by Lippert's, Bakshiev's and Kawski-Chamma-Viallet's were used to find excited state dipole moments and it is found that excited state dipole moments are larger than ground state dipole moments in all the three molecules. This may be due to the fact that, the excited states for all the three molecules are more polar than the ground states. Furthermore, we have analysed the microscopic solvent polarity parameter and effect from empirical measurements of acidity (SA), basicity (SB), polarizability (SP) and dipolarity (SdP).