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.

New synthetic methods for heterocyclic 1,3,2-dithiazolyl (DTA) radicals have been developed, and trends in the molecular spin distributions and electrochemical properties of a series of DTA radicals are reported. The crystal structures of [1,2,5]thiadiazolo[3,4-f][1,3,2]benzodithiazol-2-yl (TBDTA) and [1,3,2]pyrazinodithiazol-2-yl (PDTA) have been determined. The structure of TBDTA (at 293 and 95 K) contains two molecules in the asymmetric unit, each of which generates pi-stacked arrays, one consisting of antiparallel chains of centrosymmetrically associated dimers, the other comprising parallel chains of unassociated radicals. The structure of PDTA (at 293 and 95 K) is simpler, consisting of slipped stacks of pi-dimers. Variable-temperature magnetic susceptibility (chi(P)) measurements on TBDTA indicate essentially paramagnetic behavior for the unassociated radical pi-stacks over the range 5-400 K. By contrast PDTA is diamagnetic at all temperatures below 300 K, but between 300 and 350 K the value of chi(P) follows a sharp and well-defined hysteresis loop, with T(C) downward arrow = 297 K and T(C) upward arrow = 343 K. These features are symptomatic of a regime of bistability involving the observed low temperature pi-dimer structure and a putative high-temperature radical pi-stack. A mechanism for the interconversion of the two phases of PDTA and related structures is proposed in which hysteretic behavior arises from cooperative effects associated with the breaking and making of a lattice-wide network of intermolecular S- - -N' and/or S- - -S' interactions.

We report the synthesis and first electronic characterization of an atomically thin two dimensional p-conjugated polymer. Polymerization via Ullmann coupling of a tetrabrominated tetrathienoanthracene on Ag(111) in ultra-high vacuum (UHV) produces a porous 2D polymer network that has been characterized by scanning tunnelling microscopy (STM). High-resolution X-ray photoelectron spectroscopy (HRXPS) shows that the reaction proceeds via two distinct steps: dehalogenation of the brominated precursor, which begins at room temperature (RT), and CC coupling of the resulting Agbound intermediates, which requires annealing at 300 C. The formation of the 2D conjugated network is accompanied by a shift of the occupied molecular states by 0.6 eV towards the Fermi level, as observed by UV photoelectron spectroscopy (UPS). A theoretical analysis of the electronic gap reduction in the transition from monomeric building blocks to various 1D and 2D oligomers and polymers yields important insight into the effect of topology on the electronic structure of 2D conjugated polymers.