Experimental studies on the determination of the dipole moments of some different laser dyes

Abstract In this paper we used the Stokes shift phenomena to determine the difference in the dipole moments of the excited state μ e and ground state μ g to be ( μ e − μ g ), and the polarizability α . In this paper, we studied six different laser dyes belonging to four different classes of laser dyes which are diolefin 2,5-Distyryl pyrazine (DSB); 1,4-Bis (-pyridyl-2-vinyl) benzene (P2VB) and p -Bis-( o -methylstyryl)-benzene (Bis-MSB) with ( μ e − μ g ) equal to 6.40, 6.70 and 2.98 Debye, respectively; anthracene class includes 10(4-acetoxyphenyl)-2-methyl-9-acetoxy anthracene (APMAA) with ( μ e − μ g ) value of 7.25 Debye; Rhodamine B (RB) with ( μ e − μ g ) value of 5.33 Debye; and Coumarin 120 (C120) with the value 3.97 Debye for ( μ e − μ g ). In addition the value of both polarizability α and the radius r of each investigated laser dye molecule are determined. Therefore, the ratio α / r 3 for each dye is calculated to be 0.93, 0.79, 0.39, 0.37, 0.67 and 0.76 for DSP, P2VB, Bis-MSB, APMAA, RB and C120, respectively. The values of r are 4.83, 4.83, 4.90, 5.34, 5.75 and 4.11 A for the above consequence laser dyes. These dyes are studied in a large number of different solvents. The values obtained of ( μ e − μ g ) for these selected dyes are positive, which means that the excited state is more polar than the ground state.