Energetic and Structural Insights into the Molecular and Supramolecular Properties of Rubrene

Abstract

The molecular and supramolecular structure and energetics of tetracene and rubrene were investigated by a combined experimental and theoretical study. Accurate equilibrium vapour pressures at various temperatures were measured for both compounds. For rubrene the energetic analysis evidences lower crystal packing efficiency, strong molecular destabilization and confirms the non‐planar twisted equilibrium structure in the gas phase. The results also indicate that phenyl internal rotation in rubrene is highly hindered. The intra‐ and intermolecular interactions in crystal tetracene and rubrene were evaluated by computational methods. The representative stacked dimer of the tetracene⋅⋅⋅tetracene interaction in rubrene has lower ionization energy than the one modelling the same interaction in tetracene, due to stronger cation⋅⋅⋅π interactions in the cation‐radical of rubrene. Charge distribution in the cation dimer is symmetrical in rubrene, whereas in tetracene it is largely localized on the C−H⋅⋅⋅π donor partner of the herringbone dimer. These findings highlight the impact of cation⋅⋅⋅π interactions on the semiconducting properties of OSCs.

Benchmark Thermochemistry of Polycyclic Aromatic Hydrocarbons

“…Large discrepancies both with the previous experimental data and with the results of calculations were obtained for benz[a]anthracene (16), 32 chrysene (18), 32 and benzo[a]pyrene (23); 24 however, the authors indicate a large uncertainty in the measured values (Table 1). The new experimental data for fluorene (8) 27 and naphthacene (15) 31 are in much better agreement with the calculated values, but a noticeable discrepancy still remains, which does not allow us to consider these compounds as reference compounds. The problem of the discrepancy between the experimental and theoretical enthalpy of formation values of fluorene was also discussed earlier.…”

“…The structures of all compounds studied in this work are shown in Figure . In previous quantum chemical calculations, the estimated Δ f H 298 ° values were compared with the experimental values recommended by Roux et al, while the new experimental data for some of these compounds were obtained later. − These experimental data are also used in this work to make a choice of reference set of PAHs.…”

The crystalline state of rubrene materials: intermolecular recognition, isomorphism, polymorphism, and periodic bond-chain analysis of morphologies

“…They were corrected for the energy required to convert the tetracene backbone from the twisted conformation of vapor or solution to the planar one found in crystals, assuming an average value of 10 kJ mol −1 from the 6–16 kJ mol −1 range. 18,20,36,43…”

“…They were corrected for the energy required to convert the tetracene backbone from the twisted conformation of vapor or solution to the planar one found in crystals, assuming an average value of 10 kJ mol À1 from the 6-16 kJ mol À1 range. 18,20,36,43 Surface energies per unit area g hkl = W hkl /2A hkl were estimated for a reference molecule attached to the (hkl) plane, where W hkl is the separation work required to split an infinite crystal along the (hkl) plane and A hkl is the 2D unit cell area. W hkl has been estimated with the same E mm values used for attachment energies, with just minor approximation thanks to the fast decay of intermolecular (mainly dispersion) energies with distance.…”

Thermal Control of Intermolecular Interactions and Tuning of Fluorescent-State Energies

“…The possibility of establishing these hetero-molecular interactions inspired us to exploit the solid/liquid transition of EC to reversibly control the energy transfer between DMA excimer-like species and dyes with suitable absorption and fluorescence properties. As proof-of-concept, we selected the highly absorbing (ε 528nm = 1.1 × 10 4 mol –1 dm 3 cm –1 ) and emitting (Φ = 0.98) RUB as energy acceptor because of its good absorption overlap with the emission of the DMA excimer-like species (500–550 nm) and because the excitation and emission spectra of RUB show, under the experimental conditions used, negligible variations (see Figure S13) in the liquid to solid phase transition. In particular, the EC solidification should make operative the intermolecular interactions between DMA and RUB and consequently the RUB emission is expected to be activated upon DMA excitation through energy-transfer processes involving DMA excimer-like species.…”