Transient absorption of the probe beam by the erythrosine triplet in pulsed-laser thermal lens spectrometry: the influence of the solvent, oxygen and dye concentration

Transient absorption of the probe beam by the erythrosine triplet generated by excitation laser is evidenced in pulsed-laser thermal lens spectrometry. The transient absorption signal and thermal lens signal exhibit nonlinear dependences against excitation energy accounting for photobleaching of ground-state species with subsequent production of metastable triplets. By careful adjustment of the probe and excitation beam waists into the sample cell, the thermal lens signal can be removed and only the transient absorption signal detected. The lifetime of the triplet state is investigated from the decay rate constant of the transient signal. In nitrogen-saturated solutions, the decay rate depends on the solvent and dye concentrations. The quenching rate constants obtained in homogeneous solvents, such as water and ethylene glycol, are typical of diffusion-controlled reactions and depend on the viscosity. In aqueous micellar solutions, self-quenching is less operative due to the protecting effect of micelles and the triplet state would deactivate mainly by unimolecular decay.