Pixel International Conferences

In this contribution, we present various experiments with pyridine copper(I)iodide complexes that address aspects such as fluorescence in general as well as fluorescence thermochromism in particular. The latter describes the fascinating phenomenon of changing the fluorescence color reversibly in dependence of temperature [1]. In the experiments, the number of pyridine ligands is successively reduced by drying and subsequent heating of the prepared solution, which at first causes an irreversible change in the emitted fluorescence radiation under UV light. The fluorescence properties of the complexes obtained can then be reversibly influenced by cooling with liquid nitrogen. This phenomenon can be explained by the different energy levels of possible excited electronic states and therefore influencing the energy gap to the ground state, resulting in a change of fluorescence color. The probability of occurrence of these states changes with temperature and is caused by different temperature-dependent distortions of the complex geometry [2,3]. The presented experiments show an interesting play of colors and can be easily performed in experimental classes. At the same time, they provide good didactic opportunities to connect aspects of several basic concepts in chemical education (energy as well as structure-property relationship) and to teach them in an impressive way. Accompanying material for teachers and students developed for this purpose will also be presented.

Keywords: fluorescence, fluorescence thermochromism, school experiments, energy.

References:

[1] H. D. Hardt, A. Pierre (1973). Z. Anorg. Allg. Chem., 402(1), 107-112.
[2] F. Parmeggiani, A. Sacchetti (2012). Journal of Chemical Education, 89, 946-949.
[3] P. C. Ford, A. Vogler (1993). Acc. Chem. Res., 26, 220-226.