Stille coupling of 2-and 3-(tributylstannyl)thiophene derivatives with tetrabromobenzene followed by oxidative cyclization provides a simple, two-step synthetic route to two isomeric tetrathienoanthracene structures (13 and 14). The materials are characterized by a remarkable thermal stability, both in air (T dec ≈ 400 °C) and under nitrogen (sublimed with no decomposition at 450-500 °C). Optical studies of the parent and alkylated compounds showed sky-blue photoluminescence with quantum yields ranging between 0.17 and 0.40 and Stokes shifts of 0.03-0.16 eV. Both the optical properties and electrochemical behavior depend strongly on the position of the heteroatoms. Structural studies with X-ray crystallography (for 3D single crystals) and scanning tunneling microscopy (for 2D monolayers) indicate a high level of order, with similar intermolecular interactions for both isomers. The alkylated materials 13b and 14b have been used to fabricate thin-film transistors by both vacuum evaporation and solution processing. The preliminary studies show (unoptimized) hole mobilities of up to 7.4 × 10 -2 cm 2 V -1 s -1 and very high on/off ratios of up to 1 × 10 8 for vacuum-deposited films. The isomer 13, which showed higher thermodynamic stability of the radical cation and stronger intermolecular S • • • S contacts, also revealed better device performance.

Synthetic methods have been developed to generate the complete series of resonance-stabilized heterocyclic thia/selenazyl radicals 1a-4a. X-ray crystallographic studies confirm that all four radicals are isostructural, belonging to the tetragonal space group P42(1)m. The crystal structures consist of slipped pi-stack arrays of undimerized radicals packed about 4 centers running along the z direction, an arrangement which gives rise to a complex lattice-wide network of close intermolecular E2---E2' contacts. Variable temperature conductivity (sigma) measurements reveal an increase in conductivity with increasing selenium content, particularly so when selenium occupies the E2 position, with sigma(300 K) reaching a maximum (for E1 = E2 = Se) of 3.0 x 10(-4) S cm(-1). Thermal activation energies E(act) follow a similar profile, decreasing with increasing selenium content along the series 1a (0.43 eV), 3a (0.31 eV), 2a (0.27 eV), 4a (0.19 eV). Variable temperature magnetic susceptibility measurements indicate that all four radicals exhibit S = 1/2 Curie-Weiss behavior over the temperature range 20-300 K. At lower temperatures, the three selenium-based radicals display magnetic ordering. Radical 3a, with selenium positioned at the E1 site, undergoes a phase transition at 14 K to a weakly spin-canted (phi = 0.010 degrees) antiferromagnetic state. By contrast, radicals 2a and 4a, which both possess selenium in the E2 position, order ferromagnetically, with Curie temperatures of T(c) = 12.8 and 17.0 K, respectively. The coercive fields H(c) at 2 K of 2a (250 Oe) and 4a (1370 Oe) are much larger than those seen in conventional light atom organic ferromagnets. The transport properties of the entire series 1a-4a are discussed in the light of Extended Hückel Theory band structure calculations.

A new NON-donor ligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H 2 -[XA 2 ], 1), was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with the appropriate dibromoxanthene precursor. Stable K 2 (dme) 2 [XA 2 ] (2) and Na 2 [XA 2 ] (3) salts were accessible by deprotonation of H 2 [XA 2 ] with KH in dme or NaH in toluene. The thermally unstable lithium salt of McConville's 2,6-bis(2,6-diisopropylanilidomethyl)pyridine ligand (Li 2 [BDPP], 4) was isolated by deprotonation with nBuLi or LiCH 2 SiMe 3 in hexanes at low temperature. Reaction of [ThCl 4 (dme) 2 ] with Li 2 [BDPP] or M 2 (dme) n [XA 2 ] resulted in the formation of pentagonal bipyramidal [LThCl 2 (dme)] complexes (L ) BDPP, 5; XA 2 , 6). Subsequent reaction of 5 or 6 with LiCH 2 SiMe 3 gave base-and salt-free dialkyl complexes, [LTh(CH 2 SiMe 3 ) 2 ] (L ) BDPP, 7; XA 2 , 8), which are stable for days in solution at 90 and 70°C, respectively. Complexes 5, 7, and 8 were also accessible by initial combination of 2 or 4 equiv of LiCH 2 SiMe 3 with [ThCl 4 (dme) 2 ], followed by addition of H 2 L. These reactions likely proceed by alkane elimination, but dialkyl or tetraalkyl thorium intermediates were not identified. The X-ray crystal structure of 8 suggests the presence of R-agostic C-H-Th interactions for both alkyl groups. In solution, 7 and 8 exhibit temperature-dependent 1 J C,H coupling constants for ThCH 2 , demonstrating the presence of R-agostic interactions which become increasingly favored at lower temperature. Reaction of 5 with Li 2 [BDPP] at 0°C or 7 with H 2 [BDPP] at 100°C resulted in the formation of extremely sterically encumbered [Th(BDPP) 2 ] (9), which adopts a highly distorted six-coordinate geometry with the four anilido groups arranged in an approximate tetrahedron around thorium. Bisligand complexes were not accessible with the XA 2 platform, presumably due to increased ligand rigidity.