Pyrene Fluorescence To Probe a Lithium Chloride-Added (Choline Chloride + Urea) Deep Eutectic Solvent

Deep eutectic solvents (DESs) have shown promise as environmentally benign and inexpensive media with superior properties. Because of their structural features, they have potential to be versatile alternatives to the conventional electrolytes in various applications in science and technology. A mixture of a common and popular DES Reline, composed of salt choline chloride and H-bond donor urea in a 1:2 mole ratio, and lithium salt LiCl is investigated in a 298.15–358.15 K temperature range using a well-known multidimensional fluorescence probe pyrene. The band 1-to-band 3 emission intensity ratio (Py I1/I3) at a given temperature reveals no change in the dipolarity of the pyrene cybotactic region of Reline on addition of up to 2.093 m(LiCl). Decrease in dipolarity of the medium on increasing temperature becomes less pronounced in the presence of LiCl. Excited-state intensity decay of pyrene fits best to a two-exponential decay equation irrespective of the temperature and LiCl concentration. While the short...