Tetracene rubrene

Fig. 6 Absorbance spectra for solution (dotted trace) and thin film (solid trace) samples of rubrene in the upper panel and tetracene in the lower panel. Molecular aggregation in the tetracene thin film gives rise to the splitting of its absorption bands. Inset are chemical structures for rubrene and tetracene...

Reduction of the hydrocarbon 5,6,11,12-tetraphenyltetracene (rubrene) with a sodium mirror in THF gave a dark green solution from which almost black crystals of the tetrakis-sodium salt 83 could be obtained.1353 Two of the four sodium cations (each doubly solvated by THF) are located (Fig. 53) above and below the central tetracene skeleton and the other two are between pendant phenyl groups. The central sodium ions are 8-coordinate with Na-C 260-263 pm to the phenyl-substituted and 272 pm to the other... 

Fig. 12. Perrin quenching radii, R, [33J vs. variations of the free energy, - AG°, of electron transfer from the excited donor molecule to the acceptor molecule for donor-acceptor pairs in vitreous /nms-l,5-decalindiol. 1, Rubrene + A/ AT-diethylamline (DEA) 2, rubrene + N,N,-Ar,Ar-tetramethyl-p-phenylenediamine (TMPD) 3, rubrene + tetrakis(dimethylaminoethy-lene) 4, tetracene + DEA 5, tetracene + TMPD 6, 9,10-dinaphthylanthracene + DEA 7, 9,10-dinaphthylanthracene + TMPD 8, perylene + DEA 9, perylene + TMPD 10, 9-methylanthracene + TMPD 11, 9,10-diphenylanthracene + TMPD 12, coronene + TMPD 13, benzo[ Ai jperylene + TMPD 14, fluoranthene + DEA 15, acridine + DEA.

Comparing single crystal and vapor-grown devices for these two compounds is difficult, because reports on evaporated tetracene OTFTs are rather scarce [99-101], and despite several (unpublished) attempts, fabrication of an operating thin-film device from rubrene has not yet been successfully achieved. For both compounds the problem seems to arise from an improper deposition mechanism, which, in contrast with experience with pentacene and sexithiophene, does not favor two-dimensional growth. 

E i1 = 0.9eV), tetracene CEg1 = 2.37eV, Ex,— 1-27 eV) and rubrene (Sg1=2.33eV, Ex,— 1-2 eV), and their fluorescence quantum yield is known to be very low at room temperature, strongly increasing as temperature decreases. Examples are shown in Fig. 34. In the case of neat tetracene and rubrene, the fluorescence efficiency increases as the temperature is lowered because of the suppression of the thermally activated singlet exciton fission channel [cf. y s in (80) and (82)]. 

Figure 34 The relative fluorescence intensity plotted as a function of temperature, for crystalline tetracene (see Ref. 200), rubrene (see Ref. 201) and tetracene doped with pentacene green and red emission component as shown in the inset) (see Ref. 202).

The IP values of neutral electron donor molecules used as components for organic metals are within the limits of 6.3 < IP < 6.9 eV. These low IP values are exhibited by several classes of organic compounds. Thus IP values of arenes decrease rapidly in a series of linearly annelated polyacenes (Table 1). Tetracene (4) and especially pentacene (5) and rubrene (6) can... 

Auch das leuchtend rote 9,10,11,12-Tetraphenyl-tetracen, das Rubren, ist diamagnetisch (43). Dieser Kohlenwasserstoff ist aber so reaktions-fahig, daB er bei Bestrahlung mit sichtbarem Licht leicht Sauerstoff aufnimmt unter Entfarbung und Bildung eines reversibel spaltbaren Photo-oxyds. Die Acene kann man daher nach ihrem gesamten Ver-halten in die Klasse Biradikaloide einreihen. 

Figure 52. Plot of the stretch exponent (5A of the probe correlation function against the ratio, T /i g, of the probe correlation time to the host a-relaxation time t / . T/PS denotes the probe tetracene (T) in the host polystyrene (PS). Other probes are anthracene (A), BPEA, rubrene (R), and the PS spheres (PS-ONS). The other hosts are polysulfone (PSF), tri(naphthal benzene) (TNB), orhto-terphenyl (OTP), polyisobutylene (PIB), and phenylphthalein-dimethylether (PDE).

Analysis of the vibrational bands revealed that at earliest growth stages the film is amorphous. In particular, a broad band at 1373 cm-1 proves the amorphous nature of the film. On the other hand, the mode at 1606 cm-1, usually an infrared active band, proves a symmetry breakdown of the molecule at this growth stage. Additionally, the amorphous phase lacks of vibrational activity at the phenyl groups, and tetracene backbone. Therefore, it is likely that the geometry of the rubrene molecule is dramatically distorted. 

Further growth leads to seeding of spherulites in the amorphous matrix and further to their coalescence. This growth phase associated with spherulite-like shapes (spherulites in amorphous matrix and coalesced spherulites) was found to be highly sensitive to the light polarization, which is shown by the phenyl group band (1303 cm4) and the tetracene core band (1522 cm-1). That proves clearly the crystalline nature of the rubrene in the spherulites. 

Rubrene. This organic semiconductor consists of a tetracene core with four additional phenyl groups connected by single bonds. In contrast to the desired crystalline phase the amorphous one is not stable against oxidation [10], The two states can be distinguished easily, since the amorphous phase lacks the typical red color found for crystalline films. 

The recovery time following upon bleaching induced by Si-Sji absorption of p-terphenyl in cyclohexane at room temperature is found to be about 380 ps. The temperature dependence of photophysical processes in perylene, tetracene, and some derivatives is shown to arise from thermal activation of the S1-T2 intersystem crossing process and also for the Si-Sq internal conversion, which is particularly important in rubrene. ... 

FIGURE 2.1.2 Single crystals of rubrene and tetracene grown from the vapor phase. 

A density-independent ft has been observed in devices based on single crystals of rubrene [30,35,36], pentacene [33,34], tetracene [31], and TCNQ [39]. This important characteristic of single-crystal OFETs contrasts sharply with a strongly Vg-dependent mobility observed in organic TFTs [64] and a-Si H FETs [65]. In the latter case, the density of localized states within the gap is so high that the Fermi level remains in the gap even at high jl/gl values. 

From the Hall data, the density of mobile carriers in the OFET s channel can be directly determined for the first time, without the assumptions regarding the gate-channel capacitance Q. Hall effect studies in other organic semiconductors (e.g., pentacene and tetracene) are highly desirable because most of the OFETs based on those materials still operate in the trap-dominated regime and the intrinsic mobilities at the surface of these semiconductors, To(7), are unknown. The Hall measurements, however, are complicated by a very high sheet resistance of the conduction channel typical for OFETs, which often exceeds 10 MO/square. For this reason, the first demonstration of the Hall effect appeared only recently, due to the high carrier mobility in rubrene [82,83]. 

FIGURE 2.1.21 Left the Hall mobility versus T for a rubrene OFET in the double-log scale (compare with Figure 2.1.20). (From Podzorov, V. et al., Phys. Rev. Lett., 95, 226601, 2005.) Right the calculated T-dependences of the hole mobility for different crystallographic directions in tetracene. (From Hannewald, K. and Bobbert, P. A.,AIP Conf. Proc. 772, 1101, 2005.)... 

O. Ostroverkhova, D. G. Cooke, F. A. Hegmann, J. E. Anthony, V. Podzorov, M. E. Gershenson, O. D. Jurchescu, and T. T. M. Palstra. Ultrafast carrier dynamics in pentacene, functionalized pentacene, tetracene, and rubrene single crystals. Applied Physics Letters, 88(16) 162101-3, 2006. 

The simulated current-voltage characteristic (Fig. 8.30) corresponds roughly to the experimentally-determined characteristics for rubrene and tetracene crystals in the non-ohmic range (Fig. 8.27). For the ultrapure tetracene crystals, the values fx 1 cm /Vs for the mobility at room temperature and Nt<5-10 cm , Et 700 meV for the density and the depth of the charge-carrier traps were found [37]. 

Rubrene, a tetraphenyl derivative of tetracene, has recently attracted much attention since hole mobilities as high as 20 cm /V s at room temperature have been reported. In addition, the temperature... 

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