Electronic structure of conducting organic polymers: insights from time-dependent density functional theory

Saturated organic polymers that have revolutionized material science in the 20th century are electrical insulators

Ulrike Salzner

2014

Saturated organic polymers that have revolutionized material science in the 20th century are electrical insulators
Knowing that orbital energies are reliable with appropriate choice of the density functional is extremely useful for research on conducting organic polymers because determining ionization potential by calculating inner valence states requires inclusion of hundreds of excited states, which is impossible for very long oligomers and polymers
Experiments on medium-sized oligomers with 3–8 thiophene rings showed identical spectral changes upon doping as seen in thin-film experiments, but revealed that two sub-gap transitions are associated with singly charged species rather than with dications
The two peaks in singly oxidized thin films suggest that charge carriers in COPs are polarons and not bipolarons
For longer oligomers, the absorption band of the neutral species decreases upon doping with one equivalent of dopant to about half its intensity but does not vanish
density functional theory and time-dependent density functional theory can both be applied to oligomers that are long enough to address crucial properties
Trends among different polymers are well reproduced with either type of functional

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