Rubrenes: Planar and Twisted

Abstract

Surprisingly, despite its very high mobility in a single crystal, rubrene shows very low mobility in vacuum-sublimed or solution-processed organic thin-film transistors. We synthesized several rubrene analogues with electron-withdrawing and electron-donating substituents and found that most of the substituted rubrenes are not planar in the solid state. Moreover, we conclude (based on experimental and calculated data) that even parent rubrene is not planar in solution and in thin films. This discovery explains why high mobility is reported in rubrene single crystals, but rubrene shows very low field-effect mobility in thin films. The substituted rubrenes obtained in this work have significantly better solubility than parent rubrene and some even form films and not crystals after evaporation of the solvent. Thus, substituted rubrenes are promising materials for organic light-emitting diode (OLED) applications.

Rubrene: The Interplay between Intramolecular and Intermolecular Interactions Determines the Planarization of Its Tetracene Core in the Solid State

“…-2 to -4 kcal mol -1 over the constrained-planar tetracene backbone, a result consistent with previous theoretical studies. [17][18][19][20][21] The degree of twisting, defined as θ B in Figure 2, falls between 30 to 40°. The nearly equivalent energy differences across the series between the (constrained) planar and (relaxed) twisted backbones indicate that the exact nature and positions of the substituents on the phenyl rings seem to have only a small effect on the energetics of the (Table S5) more stable than conformations with twists similar to those in rubrene; 41 hence, the tetracene backbone finds itself in a highly unfavorable conformation in rubrene.…”

“…21,[24][25][26] Examples of this conformational variation are shown in Figure 1 where crystals of 1, 3, and 5 have planar tetracene cores, while in crystals of 2 and 4 the tetracene 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 backbones substantially twist. Rubrene derivatives that maintain planar tetracene backbones can have intermolecular electronic couplings that even surpass that of the parent compound 1 (though their charge-carrier mobilities in single-crystal field-effect transistors currently remain below those for 1).…”

High‐Yielding Synthesis and Full Spectroscopic Characterization of 5,6:11,12‐Di‐o‐phenylenetetracene and Its Synthesis Intermediates

“…A facile separation of both compounds was achieved by fractional crystallization from hot n-butyl acetate. In addition to the original routes of Dufraisse, [30] Yagodkin, [41] and Badger and Pearce, [40] Paraskar et al [44] in 2008 presented a promising alternative approach to 4 to which our attention was drawn.…”

“…According to Paraskar et al, [44] the Diels-Alder reaction of DPhIBF (1) and 1,4-naphthoquinone (2), followed by in situ deepoxidation using BBr 3 as a Lewis acid catalyst gives 4. This strong Lewis acid induces a double E1 elimination, which decreases the charge density at the oxygen in the naphthoquinone-like unit.…”

“…Complete schematic overview of the most important reaction sequences towards 8 from intermediate 4. The initial routes of Dufraisse [30] and Bergmann [39] were confirmed by characterizing the intermediate reaction products completely and were further developed by the protocols of Badger and Pearce, [40] Yagodkin, [41] and Paraskar [44] and their co-workers. Our successful final route to DOPT is shown in the box.…”