Ab initio study of the optical properties of crystalline phenanthrene, including the excitonic effects

• Phenanthrene and anthracene show high anisotropy in their optical spectra.
• While, for phenanthrene, onset is characterized by two spin-singlet excitation features, anthracene spectra show one.
• The spin-singlet exciton binding energies in phenanthrene are larger than exciton binding energy in anthracene, a result of the shorter molecular length of phenanthrene.
• Some singlet–triplet splittings in phenanthrene have negative values showing the less stable singlets.

Using the ab initio methods for solving the Bethe–Salpeter equation on the basis of the FPLAPW method, optical properties of crystalline phenanthrene were calculated, in a comparison to its isomer, anthracene. It was found that despite the similarity of the structural, electronic, and the overall optical properties in a 40 eV energy range, phenanthrene and anthracene show significant differences in their optical spectra in the energy range below band gaps. Phenanthrene has two spin singlet excitonic features whereas anthracene shows one. The singlet and the lowest triplet binding energies of phenanthrene were found to be larger than anthracene. In this study, in addition, a comparison has been made between the optical spectra in RPA and the existing experimental data.

Figure optionsDownload as PowerPoint slide