Theoretical determination of the geometric and electronic structures of oligorylenes and poli(peri-naphthalene)

Abstract

We present a theoretical investigation of the electronic structure of oligorylenes (from perylene to heptarylene, including also the naphthalene molecule) and their corresponding polymer poly(peri-naphthalene) (PPN) using the nonempirical valence effective (VEH) method. The geometry of the unit cell used to generate the polymer is extrapolated from the PM3-optimized molecular geometries of the longest oligorylenes. That geometry shows some bond alternation along the perimeter carbon chains and a bond length of ≊1.46 Å is calculated for the peri bonds connecting the naphthalene units. The VEH one-electron energy level distributions calculated for oligorylenes are used to interpret the experimental trends reported for the first ionization potentials, redox potentials, and lowest energy optical transitions. An excellent agreement is found between theoretical estimates and experimental values. The VEH band structure calculated for an isolated chain of PPN is interpreted in terms of the molecular orbitals of naphthalene. The ionization potential, electron affinity, and bandwidths obtained for PPN suggest a large capacity to form conducting p- or n-type materials. The small band gap of 0.56 eV predicted for PPN from VEH band structure calculations is in good agreement with theoretical and experimental estimates calculated by extrapolating the data reported for the oligomers.