Heptazines are promising molecular building blocks for photocatalysis, OLEDs and energy storage. Researchers at CEA-IRIG/SyMMES/CAMPE & STEP have now demonstrated that new substituents can be efficiently introduced onto these structures thanks to several molecular coupling reactions unprecedented for this family of compounds. This breakthrough opens the way to tailor-made molecules and materials for energy and optoelectronic applications.

Researchers demonstrated that classical carbon–carbon cross-coupling reactions* widely used in organic chemistry — including Suzuki, Sonogashira, Stille, Kumada and Negishi couplings — can be efficiently applied to heptazine derivatives, although they had previously proven unsuccessful with this family of compounds. By choosing to use mono-halogenated heptazines, which are more stable and soluble than the conventionally used precursors, the team obtained an unprecedented series of substituted derivatives in yields ranging from 67 to 82%.The study also shows that the electronic nature of the substituents strongly influences the redox and optical properties of the molecules: some derivatives display red-shifted visible-light absorption and very intense emission (up to 80% quantum yield). These findings establish valuable structure–property relationships for the design of future redox/photoactive compounds.

These new functionalization strategies facilitate the design of heptazine derivatives with tunable properties for applications in energy conversion, photocatalysis and organic electronics.

*In organic chemistry, a cross-coupling reaction is a coupling process between two molecular fragments through the formation of a carbon–carbon bond mediated by an organometallic catalyst. The organometallic compound R–M reacts with an organic halide R'–X to form the product R–R'.