Energy Dispersions of Anisotropic Refractive Indices of Thiophene/Phenylene Co-Oligomer Crystals

Abstract

We have determined the energy dispersions of the anisotropic refractive indices along the three a-, b-, and c-crystal axes of the thiophene/phenylene co-oligomer (TPCO) crystals with higher precision. The refractive indices were calculated from interference fringes observed in the vertical- and oblique-incidence transmission spectra of single crystal thin films. The optical constants of the TPCO crystals have large optical anisotropy and strong energy dispersion because of the molecular transition dipole moments oriented as H-aggregates. In particular, the refractive index of the c-axis and its energy dispersion are much larger than those of the other axes. The strong energy dispersion of the refractive indices results in the large effective refractive indices of the TPCO crystals. The determined refractive indices along the three crystal axes of BP1T crystals are very useful for optical device applications.