Although it would be difficult to describe in detail the evolution of the
science of condensed organic molecular solids over the past century, rec￾ognizable periods of activity can be identified. An abbreviated outline of the
lineage might be as follows: Evolving from a diverse array of work from
many different backgrounds and disciplines, there was a surge in interest in
the 1970s in the metallic one-dimensional charge transfer salts, as repre￾sented by the molecular crystal TTF-TCNQ, and in parallel, in the interca￾lated graphites. Based initially on these two classes of materials, the ter￾minology synthetic metals was coined. The discovery of electrically
conducting organic polymers in the late 1970s provided a new focus for the
field and resulted in a natural scientific reorganization. During the 1980s,
conducting polymers matured as a unique class of materials: stable electronic
materials that combined the electrical and optical properties of metals and
semiconductors with the processing advantage and mechanical properties of
polymers. Organic (small-molecule) light-emitting devices (OLEDs)
emerged in the 1980s and became a new focus for research and development
in the 1990s. Light-emitting devices based on luminescent, semiconducting
polymers (PLEDs) evolved in the 1990s along with the more general de￾velopment of ‘‘plastic electronics,’’ including photodiodes, photovoltaic
cells, thin-film transistors, and lasers. Although we have only just entered
the first decade of the new century, it seems that a principal focus will be
on the use of advanced printing technologies to fabricate such plastic elec￾tronic devices