Pyrene excimer emission was observed with the addition of iodide anions, showing that this salt changed the structure of the NaDC aggregates leading to the binding of some pyrene molecules in close proximity. A decrease of the pyrene monomer emission intensity (350-430 nm) and a small increase in the pyrene excimer emission intensity above 450 nm were observed as the iodide concentration was raised (Figure ). The ratio of the emission intensities at 470 and 380 nm, increased from 0.019 to 0.059 when the iodide anion concentration was raised to 91 mM. The addition of sodium chloride to the OTPh/NaDC/pyrene gel (Figure ) also led to the observation of excimer emission, showing that the presence of the pyrene excimer emission was due to an ionic strength effect. The pyrene emission intensities were similar in the presence sodium iodide and sodium chloride. Therefore, the quenching of pyrene monomers by iodide anions could not be determined from steady-state fluorescence studies and required time-resolved measurements, since the ionic strength effects could be dependent on the nature of the ions.