organic semiconductors

Low molecular weight organic compounds comprising conjugated bonds are semiconductors, such as organic dyes, compounds with condensed aromatic rings, the conjugated chain bonds of semiconductor compounds may contain carbon, nitrogen, oxygen and carbon atoms. sulfur. other semiconductor compounds are coordinator polymers (iron, copper, cobalt, nickel, maghnnesium, zinc, mercury, cadmium).
The products obtained by irradiation and heat treatment of polyethylenes are also semiconductors.
The electronic structure of all these compounds is characterized by conjugate bonding of electrons, between the groups containing conjugated electrons can exist bridges, so that the electronic delocalization of a single electron is manifested only within the limits of a segment of a chain comprising only two to seven monomers.
According to A.Dulov, the short length of a continuous conjugation chain is an indication in favor of an electronic structure common to all organic semiconductors, since this length is of the order of that found in conjugated systems of low molecular weight semiconductor compounds.
As the temperature increases, the conduction increases according to an exponential law. The conduction is electronic and not ionic, since after passage of a current there is no trace of polarization. In the majority of the cases the current carriers are negative, they are electrons, although the conduction by holes is also possible, the conduction by holes is probably due to an adsorption of oxygen.
A compact and regular assembly of polymer chains in a crystal lattice favors intermolecular interactions and electrical conductivity, on the other hand the heat treatments which degrade the molecular crystals sometimes reveal a specific unordered structure.
In a polymer containing a long polyene chain, an excited state can appear all along the chain, which could give rise to the appearance of superconductivity at room temperature.