Electronic and chemical properties of cyanated, halogenated and thiophene-based linear acene derivatives by first-principles calculations

Molecular modeling plays an essential role in searching for new and better organic electronic materials with excellent electronic and chemical properties to design organic electronic devices. In this research, we have studied some electronic, chemical and vibrational properties of linear acenes (from benzene to heptacene), and the additional effect of halogens, cyanate, and thiophene to linear acenes. The possible molecular properties of linear acenes and their derivatives as a function of a number of the fused benzene rings and the total number of carbons were studied. The computation is carried out using NWchem 6.3 code and Molden for molecular structure visualization. Hartree-Fock (HF), Density Functional Theory (DFT) and MØller-Plesset (MP2) level of the theories with B3LYP exchange functional using 6-311G, 6-311G (d,p), 6-311G* and aug-cc-pvdz basis sets are used for calculations. The ground state energy and band gap energy decrease with number of linear acene rings while the nuclear repulsion energy and Coulomb potential increase due to the accumulation of electrons in the bonding states. Additionally, p-bonding electrons increase the highest occupied molecular orbitals (HOMO) energy, and p*-antibonding electrons decrease the lowest occupied molecular orbitals (LUMO) energy with the increase of the acene rings. The p-bonding electrons cause the resonance by delocalization of electrons around the linear acenes molecular structures. It was found that the band gap energy, chemical potential, µ and global hardness, η decrease with the increase in the number of acene rings whereas the electronegativity χ, softness S and electrophilicity ω, increase with the number of linear acene rings. The results show good agreement with theoretical and experimental values. In addition, HOMO and LUMO orbitals energy, ionisation energy, electron affinity and global indices reveal that higher linear acene rings and their derivatives exhibit excellent electronic and chemical properties. However, due to high values of HOMO orbitals energy and low values of LUMO energy lead to low ionisation potential and high electron affinity across the acene derivatives which demonstrate that the materials have more potential application in organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs) than in optical application