Solvatochromic Studies of Fluorescein Dianion in N, N-Dimethylformamide/Water and Dimethylsulphoxide/Water Mixtures

Abstract

Abstract The absorption, excitation and fluorescence spectra of the fluorescein dianion (FL2−) in N, N-Dimethylformamide (DMF)/water (H2O) and Dimethylsulphoxide (DMSO)/H2O solvent mixtures have been investigated. It is found that the absorption λmax and emission maxima EX, nax are both hypsochromic shifted when the H2O content in the solvent mixtures increases. However, the shoulder peaks λs remain constant at 483. 5nm within the range of H2O mole fraction, x= 0 to 0. 518 in a DMF/H2O solvent mixture and at 484. 4nm within the range, x=0 to 0. 304, in a DMSO/H2O mixture. Further increases in H2O content, cause a hypsochromic shift in λs. The molar energies for the electronic transition from the ground state (S0) to S1, the first excited singlet state, (ET(1)) and to S2, the 2nd excited singlet state, (ET(2)) of FL2−in the solvent mixtures are also plotted against x. Linear straight lines and intersection points are observed at x=0. 73 for ET(1) and at x=0. 51 for ET(2) in the DMF/H2O mixture and at x=0. ...