diagonalene

Diagonalene is a term used in organic chemistry to denote a class of polycyclic aromatic hydrocarbons (PAHs) in which the fused benzene rings connect along diagonal edges, creating a diagonal lattice motif across the molecule. The name combines diagonal, referring to the orientation of the linkages, with the -ene suffix common to conjugated hydrocarbon systems.

Typical diagonalene structures feature planar, highly conjugated frameworks in which adjacent rings share bonds through a diagonal contact rather than the more common peri- or ortho-fusion. This arrangement yields a zigzag pattern in the carbon skeleton and can be extended to form linear oligomers or compact nanographene-like fragments.

Synthesis of diagonalenes relies on modern carbon–carbon bond-forming strategies, including targeted cross-coupling to assemble the di-aryl precursors, followed by cyclodehydrogenation or annulation steps to create the diagonal linkages. Regioselectivity, solubility, and control of condensation reactions remain active areas of development.

Physicochemical properties of diagonalenes depend on size and substitution. They are typically highly conjugated, with substantial thermal stability and wide absorption in the UV–visible region. Electrochemical measurements show tunable HOMO–LUMO gaps, making them of interest as active materials in organic electronics and sensing.

In research contexts, diagonalene derivatives are studied as model systems for extended two-dimensional conjugation and as potential components for organic semiconductors, light-emitting devices, and photovoltaic platforms. Practical use is challenged by solubility, aggregation, and synthetic yield, but functionalized versions are under investigation.