Spectral line

Spectroscopy

Quantum mechanics

Valence (chemistry)

Phenylene

Materials science

Density functional theory

Nuclear magnetic resonance

Atomic physics

Molecule

Polymer

Physics

Organic chemistry

Ionization

Thiophene

Astronomy

X-ray photoelectron spectroscopy

Computational chemistry

Binding energy

Excited state

Chemistry

Ionization energy

Electron affinity (data page)

Journal of Applied Physics

We have investigated electronic states in the valence electron bands for the thin films of three thiophene/phenylene co-oligomer (TPCO) compounds, 2,5-bis(4-biphenylyl)thiophene (BP1T), 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), and 1,4-bis{5-[4-(trifluoromethyl)phenyl]thiophen-2-yl}benzene (AC5-CF3), by using extreme-UV excited photoelectron spectroscopy (EUPS). By comparing both EUPS spectra and secondary electron spectra between AC5 and AC5-CF3, we confirm that CF3 substitution to AC5 deepens valence states by 2 eV, and increases the ionization energy by 3 eV. From the cut-off positions of secondary electron spectra, the work functions of AC5, AC5-CF3, and BP1T are evaluated to be 3.8 eV, 4.8 eV, and 4.0 eV, respectively. We calculate molecular orbital (MO) energy levels by the density functional theory and compare results of calculations with those of experiments. Densities of states obtained by broadening MO levels well explain the overall features of experimental EUPS spectra of three TPCOs.

Electronic states of thiophene/phenylene co-oligomers: Extreme-ultra violet excited photoelectron spectroscopy observations and density functional theory calculations