The role of solid-state aggregation on the emission in molecular crystals and in their devices

The aim of this contribution is to report on the recent study of differently packed oligomers based on mixed fluorene, thiophene derivatives and on substituted thiophene oligomers, with particular reference on the influence of the overall solid-state aggregation onto the photoluminescence (PL). On the other hand, the preparation of polymers having the cited oligomers as monomeric unit, thus changing the aggregation, can enhance the emission property. The combined use of crystal structure analysis, powder diffraction analysis and molecular mechanics/crystal packing calculations allowed us to give a deeper insight between PL emission and solid-state aggregation, in its turn related to chemical structure. Other factors affecting the PL yield have to be taken into account to understand the behaviour of molecules containing both polar and mobile substituents. Moreover, some indications confirming the conclusions reached on the previous topics will be presented from LED device measurements. (C) 2002 Elsevier Science B.V. All rights reserved.