The synthesis of 1,8-naphthalimide groups containing imidazolium salts/ionic liquids using I−, PF6−, TFSI− anions and their photophysical, electrochemical and thermal properties

1,8-Naphthalimide groups containing imidazolium iodide salts of different alkyl chain length on the imidazole group were synthesized. Hexafluorophosphate and bis(trifluoromethanesulfonyl)imide salts were obtained by ion exchange reactions. The synthesized salts were characterized using a variety of spectroscopic techniques. Fluorescence emission quenching of iodide and bis(trifluoromethanesulfonyl)imide salts were studied using a ruthenium dye, whilst that of hexafluorophosphate salts were performed using tris(8-hydroxyquinoline)aluminum. Calculated fluorescence quenching rate constants were as high as 1014 M−1 s−1 and values of the Gibbs free energy of electron transfer were [−32.04/−33.68], [−17.52/−20.74] and [−26.50/−30.89] kcal mol−1 for the iodide, hexafluorophosphate and bis(trifluoromethanesulfonyl)imide salts, respectively. The thermal stability of the synthesized salts was high especially in the case of bis(trifluoromethanesulfonyl)imide salts for which values of 470–498 °C were achieved. Photostability studies of hexafluorophosphate and bis(trifluoromethanesulfonyl)imide salts were also performed; calculated photodegradation half-life values ranged from 19.25 to 48.12 h.