Relaxation phenomena of excited molecular states are abundant in all nature. They mediate such key processes as photochemical reactions or even the pathways of ordinary chemical reactions. However, for a long time the main research in electronic relaxation processes was concerned with anorganic solids, in part because of their great technological importance (photography, semiconductors ... ) in part also because these compounds were the "workhorses" of the solid state physicists. In the last 30 years, there was a steadily increasing interest in organic molecular systems, first in molecular...

During the last fifteen years the field of the investigation of glasses has experienced a period of extremely rapid growth, both in the development of new theoretical ap proaches and in the application of new experimental techniques. After these years of intensive experimental and theoretical work our understanding of the structure of glasses and their intrinsic properties has greatly improved. In glasses we are con fronted with the full complexity of a disordered medium. The glassy state is characterised not only by the absence of any long-range order; in addition, a glass is in a...