Highest occupied 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. 

The electronic structure of conjugated polymer semiconductors reflects the complex interplay between intrinsic rr-electron delocalization along the polymer backbone and strong electron-phonon coupling, and the existence of energetic and positional disorder in solution-processed thin films. In a hypothetical, infinitely straight polymer chain, the highest occupied molecular orbital (HOMO) and lowest unoccupied... 

S. Xiao, A. C. Stuart, S. Liu, W. You, Conjugated Polymers Based on Benzo[2,l-b 3,4- b JDithiophene with Low-Lying Highest Occupied Molecular Orbital Energy Levels for Organic Photovoltaics. ACS Appl. Mater. Interfaces 2009, 1,1613-1621. 

S. Xiao, et al. Conjugated polymers based on benzo [2, 1-b 3, 4-b ] dithiophene with low-lying highest occupied molecular orbital energy levels for organic photovoltaics. ACS Applied Materials Interfaces, 2009. 1(7) p. 1613-1621. 

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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