Figure 1

(a) Oscillator strength of the calculated electronic transitions of the rubrene molecule. Inset: sketch of the molecule showing the direction of the $M$, $L$, and $N$ axes. Table: direction cosines along $M$, $L$, and $N$ of the four most relevant transitions. (b) Absorbance spectrum of rubrene in chloroform solution. (c) Near-normal incidence reflectance spectra of a rubrene single crystal taken with either $a$ or $b$ polarized light and the imaginary part of the refractive index deduced from the normal-incidence absorbance spectra of a $5\mathrm{\mu }\mathrm{m}$ rubrene single crystal taken with $a$ and $b$ polarized light. Inset: scheme of the electronic energy levels from the isolated molecule to the single crystal. (d) Absorbance spectra of a rubrene single crystal at 10° and 20° angles of incidence with bc as plane of incidence and $p$ (bc) polarized light. Inset: view of the arrangement of the molecules in the ab plane and of the ${\beta }_L$ angle between the $a$ axis and the molecular backbone.Reuse & Permissions

Figure 2

(a) Near-normal incidence reflectance of a rubrene single crystal taken with $a$ and $b$ polarized light. The extrapolated reflectivity below $2.2\mathrm{eV}$ is shown with dotted lines. (b) Ellipsometry angles $\psi$ and $\Delta$ as measured (continuous lines) or generated by the fitting of the measured data (dotted lines) at different angles of incidence from 20° to 65° on the ab face of a rubrene single crystal using a plane of incidence which forms an angle $\xi =33°$ to the ac rubrene plane. Inset: sketch of the experimental configuration. (c) Real and imaginary parts of the refractive indexes ${\widehat{n}}_a$, ${\widehat{n}}_b$, and ${\widehat{n}}_c$ of rubrene single crystals obtained by the fitting of the ellispometry data. Inset: imaginary parts on an enlarged scale.Reuse & Permissions

Figure 3

(a) Polarized PL spectra acquired from the edge of the crystal along the direction of the $a$ axis, with the analyzer along the $b$ (continuous line) and the $c$ axis (dashed line). Inset: normalized PL intensity as a function of the angle formed by the analyzer axis and the $b$ axis. Inset: Image of a rubrene crystal as taken under the fluorescence microscope. (b) PL spectra acquired at a collection angle of 90° and 45°, the surface normal and the direction of collection lying in the ac plane of rubrene. Inset: Scheme of the setup used for angle-resolved PL measurements. (c,d) Angular distribution of the normalized PL intensity integrated over the whole energy range (c) or taken at $2.17\mathrm{eV}$ (d), together with the calculated distribution curves for a $c$ polarized emitting dipole (c) and for a $c$ polarized emitting dipole taking into consideration the reabsorption by the resonant $c$ polarized absorption transition.Reuse & Permissions