Preliminary Historical Remarks

In the following sections, after some preliminary historical remarks and a more precise characterisation of the charge carriers in terms of polarons, we will introduce the more important experimental methods. Afler that, we treat ultrapure crystals (Sect. 8.5) and disordered organic solids (Sect 8.6). 

All together, the organic semiconductors have increased enormously in importance both in basic research and for applications since the 1960 s. They have developed in this time from a special topic of interest to only a few researchers to a respected branch of sohd-state research which is active worldwide. 

The earliest research papers on the electrical and optoelectronic properties of fluorescing organic soUds were published in the first two decades of the 20 century. They deal with 

Pochettino [1] discovered in 1906 that anthracene is a photoconductor. The anthracene crystal was investigated later, in particular after 1950, as the prototype for photoconductivity and many other electrical, optical and optoelectronic properties 

Stark and Steubing [2] in 1908 were the first to investigate the relationship between fluorescence and the photoelectric eflect (i.e. the external photoeffect), which a few years before had been explained by A. Einstein using the quantum hypothesis of light, i. e. the concept of photons. They carried out their experiments on a large number of different organic solids. This included benzene, naphthalene, and anthracene, but also many other aromatics with N- or OH-substituents. The following quote from one of their publications is still valid today  

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Nonetheless, human beings are remarkably resilient. Historically, slightly more than 75% of those exposed to a disaster will heal on their own in time, without intervention. When the disaster involves intentional violence and human malfeasance, however, such as with 9/11, preliminary data indicate that the rates of probable PTSD (11.2%) in the metropolitan New York area may be even higher than previously thought (Sche-lenger et al., 2002). 

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