Adiabatic electron affinity of pentacene and perfluoropentacene molecules studied by anion photoelectron spectroscopy: Molecular insights into electronic properties

Pentacene (C₂₂H₁₄, PEN) and perfluoropentacene (C₂₂F₁₄, PFP) are considered promising building blocks of organic semiconductors. Using gas-phase anion photoelectron spectroscopy, the adiabatic electron affinity of PEN and PFP molecules is determined to be 1.43 ± 0.03 and 2.74 ± 0.03 eV, respectively, and the S₀-T₁ transition energies of PEN and PFP are evaluated to be 0.96 ± 0.06 and 0.72 ± 0.05 eV, respectively. Photoelectron spectra indicate that the vibronic coupling in PFP is stronger than that in PEN. Quantum chemistry calculations demonstrate that the strong vibronic coupling originates from significant structural displacement upon electron injection to PFP.