Lowest unoccupied molecular orbital polymer conjugation

Conjugated polymers are generally poor conductors unless they have been doped (oxidized or reduced) to generate mobile charge carriers. This can be explained by the schematic band diagrams shown in Fig. I.23 Polymerization causes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the monomer to split into n and n bands. In solid-state terminology these are the valence and conduction bands, respectively. In the neutral forms shown in Structures 1-4, the valence band is filled, the conduction band is empty, and the band gap (Eg) is typically 2-3 eV.24 There is therefore little intrinsic conductivity. 

Fig. 181. (a) Schematic energy band diagram for photoinduced electron transfer between semiconducting, conjugated polymers and buckminster-fullerene, CgQ. CB, conduction band VB, valence band HOMO, highest occupied molecular orbital LUMO, lowest unoccupied molecular orbital, (b) Schematic illustration of photoinduced electron transfer from the pho-toexcited conjugated polymer to C50. 

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