Quantum chemical approach toward the electronic, photophysical and charge transfer properties of the materials used in organic field-effect transistors

In this study initial molecular structures of benzene, pyrazine, pyridazine, pyridine, pyrimidine, cyclopentadiene, furan, pyrrole and thiophene have been optimized at the ground (S0) and excited (S1) states using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. We also evaluate the distribution patterns of HOMOs (highest occupied molecular orbitals) and LUMOs (lowest unoccupied molecular orbitals) for these molecules at the ground (S0) and excited (S1) states. The photophysical properties, i.e., absorption (λa), and emission (λe), have been computed by TD-DFT. The calculations regarding to reorganization energies, vertical electron affinity (EAv), adiabatic electron affinity (EAa), vertical ionization potential (IPv) and adiabatic ionization potential (IPa) of the investigated molecules have been performed by applying DFT to shed light on the charge transfer properties. The effect of heteroatoms substitution on the geometrical parameters, electronic, optical and charge transfer properties has also been investigated. It was observed that benzene, furan, pyrazine, pyridazine, pyridine and pyrimidine have higher IPa compared to that of cyclopentadiene, pyrrole and thiophene. Pyridazine, pyrazine, pyridine and pyrimidine have higher EAa than that of cyclopentadiene, pyrrole and thiophene. The benzene and cyclopentadiene have low hole reorganization energies λ(h) compared to their electron reorganization energies λ(e), so they might be used as good hole transport co-monomers. The molecules of pyrazine, pyridazine, pyridine, pyrimidine, furan, pyrrole and thiophene have the electron reorganization energies λ(e) smaller than their hole reorganization energies λ(h) revealing these would be better to design electron transport materials.

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► First comparative study of small organic molecules and co-monomers used in OFETs.
► λ(e) for pyrazine, pyridazine, pyridine, furan, pyrrole and thiophene smaller than λ(h).
► Benzene and cyclopentadiene have smaller λ(h) than λ(e), might be good as a p-type.