Optical Anisotropy and Momentum-Dependent Excitons in Dibenzopentacene Single Crystals

Abstract

High-quality single crystals of the organic semiconductor (1,2;8,9)-dibenzopentacene were grown via physical vapor transport. The crystal structure—unknown before—was determined by single-crystal X-ray diffraction; polarization-dependent optical absorption measurements display a large anisotropy in the ac plane of the crystals. The overall Davydov splitting is ∼110 meV, which is slightly lower than that in the close relative pentacene (120 meV). Momentum-dependent electron energy-loss spectroscopy measurements show a clear exciton dispersion of the Davydov components. An analysis of the dispersion using a simple 1D model indicates smaller electron- and hole-transfer integrals in dibenzopentacene as compared to pentacene. The spectral weight distribution of the excitation spectra is strongly momentum-dependent and demonstrates a strong momentum-dependent admixture of Frenkel excitons, charge-transfer excitons, and vibrational modes.

Photoluminescence spectroscopy of dibenzopentacene single-crystals: multiple emissive states across temperature, time, and magnetic field in a pursuit of exothermic singlet fission

“…In toluene, dichlorobenzene or tetrahydrofuran solution, the lowest-energy absorption of DBP assigned to S 0 -S 1 excitation occurs at around 2.34 eV and is followed by 2-3 vibrational replica at 0.15-0.18 eV. [34][35][36] Very similar absorption spectra with S 0 -S 1 transition at 2.34 eV were also obtained for DBP diluted in a polystyrene matrix in ref. 36 and in this work (Fig.…”

“…The crystal structure shown in Fig. 1 was determined at 100 K. 34 Electron diffraction measurements at different temperatures between 20 and 300 K did not show noticeable changes in diffraction pattern (Fig. S1, ESI †), and we conclude that the crystal structure remains the same in the whole temperature range studied in this work and DBP did not undergo a phase transition.…”

“…The Raman spectrum of DBP crystal in this range is quite rich and includes a stand-alone mode at 60 cm À1 and a group of peaks at 107, 127, 137, and 152 cm À1 (see ref. 34 and Fig. S8, ESI †).…”

“…Recent development of the single-crystal growth of dibenzopentacene opened the possibility to study the fundamental electronic properties of this close relative of pentacene in the well-defined structural environment. 34 In this work, we presented the first study of the photoluminescence of dibenzopentacene single-crystals. Variable-temperature measurements in the 5-300 K range revealed the presence of at least five emissive states.…”

Energy-dependent dielectric tensor axes in monoclinic α-3,4,9,10-perylene tetracarboxylic dianhydride

“…In all these cases the dielectric axes (principal axes of the dielectric tensor) are established by symmetry and coincide with the crystallographic axes. Therefore, approximative methods [6][7][8] can deliver close estimates of the tensor components, although numerical procedures must generally be used to extract accurate optical spectra from the measurements. In this context, biaxial crystals with monoclinic or triclinic symmetries are more complex.…”