Jaclyn L. Brusso

Synthesis and electronic structure of a two dimensional π-conjugated polythiophene

We report the synthesis and first electronic characterization of an atomically thin two dimensional π-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 C–C coupling of the resulting Ag-bound 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.

Unprecedented transformation of tetrathienoanthracene into pentacene on Ni(111).

The imaging and characterization of single-molecule reaction events is essential to both extending our basic understanding of chemistry and applying this understanding to challenges at the frontiers of technology, for example, in nanoelectronics. Specifically, understanding the behavior of individual molecules can elucidate processes critical to the controlled synthesis of materials for applications in multiple nanoscale technologies. Here, we report the synthesis of an important semiconducting organic molecule through an unprecedented reaction observed with submolecular resolution by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Our images reveal a sulfur abstraction and cyclization reaction that converts tetrathienoanthracene precursors into pentacene on the Ni(111) surface. The identity of the final reaction product was confirmed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). This reaction has no known literature analogue, and highlights the power of local-probe techniques for exploring new chemical pathways.

Bis-1,2,3-thiaselenazolyl radicals and their σ-bonded dimers

Resonance stabilized bis-1,2,3-thiaselenazolyl radicals associate in the solid state to afford Se–Se σ-bonded dimers.

Spin-canting in heavy atom heterocyclic radicals

A pair of isostructural bis-selenathiazolyl and bis-diselenazolyl radical conductors display weak (spin-canted) ferromagnetism with Tc values of 18 K and 27 K respectively.

Structure–property trends in π-stacked dithiazolo-dithiazolyl conductors

The resonance stabilized dithiazolo-dithiazolyl radical 1b adopts a slipped π-stack structure exhibiting weak 1-D ferromagnetic coupling; variable temperature conductivity measurements indicate σRT = 2 × 10−6 S cm−1.

Halide Influence on Molecular and Supramolecular Arrangements of Iron Complexes with a 3,5-Bis(2-Pyridyl)-1,2,4,6-Thiatriazine Ligand.

A series of iron centered complexes, namely, [Fe(Py2TTA)Cl2] (1), [Fe(Py2TTA)Br2] (2), and [Fe(μ-F)(Py2TTAO)F]∞ (3), were isolated via complexation of 3,5-bis(2-pyridyl)-1,2,4,6-thiatriazine (Py2TTAH) with various ferric halides (e.g., FeF3, FeCl3, and FeBr3). Comparison of the optical and electrochemical spectroscopy, structural analysis, and magnetic studies reveal numerous similarities between the chlorido (1) and bromido (2) derivatives, which crystallize as discrete five-coordinate iron centered complexes with coordination geometries that are intermediate between trigonal bipyramidal and square base pyramid. Conversely, the fluorido derivative (3) results in a completely different structure due to oxidation of the ligand and the formation of a one-dimensional coordination polymer held together through a bridging fluoride ion. Consequently, the spectroscopic and magnetic behavior of 3 differs significantly compared with 1 and 2. Complexes 1 and 2 exhibit paramagnetic properties typical for a mononuclear S = 5/2 system with weak intermolecular antiferromagnetic interactions at low temperatures, whereas complex 3 demonstrates significant exchange couplings within the chain and weak antiferromagnetic interchain interactions, which stabilize a canted antiferromagnetic state below 4.2 K.

Elucidating the elusive crystal structure of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine

2,4,6-Tris(2-pyrimidyl)-1,3,5-triazine (TPymT) has been synthesized using two approaches: via trimerization of 2-cyanopyrimidine at 160 °C and by the reaction of 2-cyanopyrimidine with pyrimidine-2-carboximidamide. It was found that the two different synthetic pathways to TPymT yielded either a single polymorph or a mixture of two polymorphs; both of which were studied for the first time by X-ray powder diffraction (XRPD) and synchrotron X-ray powder diffraction (SXRPD). The crystal structure of the polymorph α-TPymT was determined by single crystal X-ray diffraction (SCXRD). Crystal structures of 2-cyanopyrimidine and pyrimidine-2-carboximidamide were also elucidated by SXRPD.

Optoelectronic and structural properties of a family of thiophene functionalized 1,5-dithia-2,4,6,8-tetrazocines

The dithiatetrazocine (DTTA) ring has been functionalized with thiophene (5a), 5-hexylthiophene (5b) and 5-bromothiophene (5c), and the optoelectronic and structural properties have been probed. All three derivatives possess low-lying LUMO levels near −3.5 eV and exhibit irreversible reduction and oxidation processes. Inspection of their absorption profiles reveals a small bathochromic shift in λmax with substitution of the thiophene ring. The HOMO–LUMO band gaps, determined from electrochemical, optical and computational studies, decrease across the series in the following manner: 5a > 5c > 5b. DFT calculated frontier molecular orbitals for 5a–c (R = Me for 5b) indicate delocalized electron density over the entire tricyclic framework for the HOMO, whereas the electron density for the LUMO is localized on the DTTA ring. Single crystal X-ray diffraction on 5b,c show structures consisting of molecules with planar molecular frameworks arranged in slipped π-stack arrays. Although both compounds exhibit close intermolecular interactions, the contacts observed in 5c are between π-stacks, while they are exclusively within the π-stacks for 5b.

The effect of selenium incorporation on the bandwidth and conductivity of neutral radical conductors

The first example of an undimerized pi-stacked bis-1,2,3-thiaselenazolyl radical displays improved bandwidth and conductivity relative to an isostructural bis-1,2,3-dithiazolyl.

Applying thieno[3,2-b]thiophene as a building block in the design of rigid extended thienoacenes

The synthesis of rigid extended star-shaped thienoacenes that incorporate thieno[3,2-b]thiophene as a structural unit, either as the “core” or “arm” moiety, is described herein. Four-fold Negishi coupling of a tetrabrominated core with thienyl- or thienothienyl zincates, followed by oxidative cyclodehydrogenation, affords tetra(5-hexyl)thieno([3,2-b]thieno)anthracene, tetra(5-hexylthieno[3,2-b]thieno)acridine, tetra(5-hexylthieno)benzothieno[3,2-b]benzothiophene and tetra(5-hexylthieno[3,2-b]thieno)benzothieno[3,2-b]benzothiophene. Comparative electrochemical, optical, computational and single crystal X-ray diffraction studies were carried out on this family of star-shaped thieno[3,2-b]thiophene based molecules to demonstrate, and confirm, the conservation of rigidity upon extending the conjugation, as well as to investigate the influence of the substitution pattern and heteroatom incorporation on the optoelectronic and solid state properties.