Many qualitative structure-property correlations between diradical character and emerging molecular properties are known. For example, the increase of diradical character further decreases the singlet-triplet energy gap. Here we show that inclusion of thiophenes within a quinoidal polycyclic hydrocarbon imparts appreciable diradical character yet retains the large singlet-triplet energy gap, a phenomenon that has no precedent in the literature. The low aromatic character of thiophene and its electron-rich nature are the key properties leading to these unique findings. A new indenoindenodibenzothiophene scaffold has been prepared and fully characterized by several spectroscopies, magnetic measurements, solid-state X-ray and state-of-the-art quantum chemical calculations, all corroborating this unique dichotomy between the diradical input and the emerging magnetic properties. New structure-property relationships such as these are not only extremely important in the field of diradical chemistry and organic electronics, but also provide new insights into the versatility of π-electron chemical bonding.

Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno[1,2-a]fluorene scaffold have so far remained elusive. This work reports the preparation and characterization of 7,12-dimesitylindeno[1,2-a]fluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state. As such, both NICS and ACID calculations suggest that the indeno[1,2-a]fluorene scaffold is weakly Baird aromatic. Reduction of the unstable red solid with Cs metal produces the dianion of the title compound, from which single crystals could be obtained and X-ray data acquired, thus fully corroborating the proposed indeno[1,2-a]fluorene hydrocarbon core.

Inclusion of quinoidal cores in conjugated hydrocarbons is a common strategy to modulate the properties of diradicaloids formed by aromaticity recovery within the quinoidal unit. Here we describe an alternative approach of tuning of diradical properties in indenoindeno­dibenzo­thiophenes upon anti → syn isomerism of the benzothiophene motif. This alters the relationship of the S atom with the radical center from linear to cross conjugation yet retains the same 2,6-naphtho conjugation pattern of the rearomatized core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic, theoretical, and magnetic measurements, showing that these systems are stable open-shell singlet diradicaloids that only access their triplet state at elevated temperatures.

Haley and co-workers report the synthesis and physical characterization of a family of diradicaloids on the basis of the diindenoanthracene framework. Computations suggested that altering the external fused rings on both sides of the pentacyclic core would yield systematic changes in their open-shell properties, results that have been corroborated experimentally. This structure refinement approach provides a deeper understanding on how to tune the intrinsic properties of diradicaloid compounds in a rational and predictable manner.

Charge-carrier transport in thin-film organic semiconductors is strongly related to the molecular structure and the solid-state packing, which in turn are dependent on materials processing and device configurations. We report on the synthesis and characterization of a series of  (trialkylsilyl)­ethynyl-substituted dinaphtho-fused s-indacenes that include three regioisomers: the linear, syn, and anti isomers. Structure–property relationships are established for these antiaromatic compounds by combining X-ray diffraction with field-effect transistor measurements and density functional theory (DFT) evaluations of the electronic band structures and intermolecular electronic couplings. High-performance, solution-processed organic thin-film transistors with charge-carrier mobilities over 7 cm2/(V s) are demonstrated upon optimization of the thin-film morphology. The DFT-derived crystal band structures provide insight into the varied performance metrics observed across the materials, though the fundamental limits of performance are not reached when the film quality is poor. The totality of the results presents the antiaromatic dinaphtho-fused s-indacenes as intriguing building blocks for molecular materials for semiconducting applications.