Abstract:
Semiconducting properties have been discovered in certain classes of organic materials, with
charge transport properties different than those in conventional inorganic materials like
silicon. These classes of organic materials include long chain conjugated polymers. Polymer
systeM.S. having alternating double bond along the backbone and have a finite overlap are
commonly referred as conjugated polymers. Conductivity in these systeM.S. is due to the
extended electron pathway due to the delocalized pz electrons on the polymer backbone1-3.
The resonant coupling between the pz electrons causes the pz orbitals to split into two energy
states. The orbital with the lower energy state is the Bonding Molecular Orbital. It is also
called Highest Occupied Molecular Orbital (HOMO) since it is completely filled. The higher
energy state is the Anti-Bonding Molecular Orbital. This is unoccupied and is generally
referred to as Lowest Unoccupied Molecular orbital (LUMO). In conjugated polymer
systeM.S., due to the wavefunction overlap of neighbouring unit cells, the HOMO and LUMO
behave like bands analogous to the valence and conduction bands in inorganic
semiconductors respectively. Thus the conjugated polymers can be equated to a
semiconductor with a band gap. The optical bandgap of these conjugated polymers typically
is in the range of 1.2 3.5 eV.
