Neutral open-shell molecules, in which spin density is delocalized through a helical conjugated backbone, hold promise as models for investigating phenomena arising from the interplay of magnetism and chirality. Apart from a handful of examples, however, the chemistry of these compounds remains largely unexplored. Here, we examine the prospect of extending spin-delocalization over a helical backbone in a model compound naphtho[3,2,1-no]tetraphene, the first helically chiral open-shell hydrocarbon, in which one benzene ring is fused to [5]helicene, forming a phenalenyl subunit. The unpaired electron in this molecule is delocalized over the entire helical core composed of six rings, albeit in a nonuniform fashion, unlike in phenalenyl. In the case of a monosubstituted derivative, the uneven spin-distribution results in a selective σ-dimer formation in solution, as confirmed by 2D NMR spectroscopy. In contrast, the dimerization process is suppressed entirely when four substituents are installed to sterically hinder all reactive positions. The persistent nature of the tetrasubstituted derivative allowed its characterization by EPR, UV-vis, and CD spectroscopies, validating spin-delocalization through a chiral backbone, in accord with DFT calculations. The nonuniform spin-distribution, which dictates the selectivity of the σ-dimer formation, is rationalized by evaluating the aromaticity of the resonance structures that contribute to spin-delocalization.

We present to date the most efficient gram-scale synthesis of triangulene-4,8-dione and 12-hydroxytriangulene-4,8-dione, the precursors of Clar’s hydrocarbon, in overall yields >50%. The direct dihydroprecursors of triangulene, obtained upon reduction of triangulene-4,8-dione, were stabilized in a supramolecular complex with a tetracationic cyclophane ExBox4+ and characterized by single-crystal X-ray crystallography. This result represents the first step in an endeavor to stabilize the fragile core of triangulene in an inclusion complex in solution and solid state.

Fusing two phenalenyl units such that a Kekulé structure is obtained leads to 'biradicaloid' systems, which typically display low singlet-triplet (S-T) energy gaps. The value of the S-T gap in biradicaloids can be lowered by extending the conjugated system for an additional fused ring(s). Recently, we have described an alternative approach to decrease the S-T gap with the aid of through-space interactions that arise in helically twisted biradicaloids. Using [5]helicene-based biradicaloid 'cethrene' as an illustrative example, we have shown that the value of its S-T gap is substantially decreased when compared to that of its planar isomer heptazethrene, on account of the helical twist, inducing crucial intramolecular interactions.

Nucleophilic addition of carbon-centered nucleophiles to nanographene ketones represents avaluable late-stage method for the functionalization of zigzag nanographenes,but its use is rare in the chemical literature.U sing two model systems,non-KekulØ triangulene-4,8-dione and KekulØ anthanthrone,w ei dentify unexpected regioselectivities and uncover the rules that govern these reactions.C onsidering the large number of nanographene ketones that have been reported since the pioneering work of Eric Clar,this method enables synthesis and exploration of hitherto unknown functionalizedn anographenes.

The synthesis and optoelectronic properties of five donoracceptor molecules, featuring an electron-acceptor unit made of six fused benzenoid rings that resembles an equilateral triangle, are described. These molecular 'triangles' were synthesized in eight steps from simple building blocks such that the electron-donor substituents could be installed in the last step by means of the Suzuki cross-coupling reaction. All molecules absorb and emit visible light in the region of around 450-650 and 550-850 nm, respectively, exhibit solvatochromism, and possess up to four redox states.