Phase refractive index dispersions of organic oligomer crystals with different molecular alignments

We grew slab crystals of end-capped oligothiophenes with phenyl, biphenyl, or methyl groups and unsubstituted oligophenyls. These crystals were grown in the vapor and liquid phases. We determined their dispersions and anisotropic refractive indices from interference fringes in the emission and reflectance spectra. To do this, we used pairs of parallel facets, which were naturally formed during the crystal growth or cleaved from wide crystals, as optical resonators. The unsubstituted oligophenyls indicated blue-shifted dispersions compared with the end-capped oligothiophenes. We discussed refractive indices in connection with molecular alignments in the crystals and compared them with computational results.