A mechanochemical route to triazatrinaphthylenes: building blocks for π-extended, nitrogen-enriched two-dimensional metal–organic frameworks

Abstract

Nitrogen-containing polyaromatic heterocycles are the key molecular materials in semiconducting and optoelectronic devices, yet their synthesis typically depends on high-boiling, toxic organic solvents and multi-step catalytic processes. Herein, we report a metal-free solid-state synthetic strategy followed by thermal treatment for the efficient synthesis of the functionalized C_3h-symmetric triazatrinaphthylene (TNP) derivatives. Through rigorous optimisation of catalyst concentration, reaction stoichiometry, temperature, and time, this protocol delivers nearly quantitative yields (up to 95%) while eliminating hazardous solvents. The solid-state nature of the method also facilitated direct observation of the key reaction intermediates, such as mono- and tri-imine species, and partially cyclized products, providing mechanistic information for stepwise condensation and S_NAr-mediated aromatisation. Importantly, our synthetic approach allowed access to a hexa-hydroxy TNP ligand TNP(OH)₆, which was further employed to construct a two-dimensional Cu(II)-based metal–organic framework (Cu–TNP). The resulting MOF exhibits high crystallinity, efficient π–π stacking, and a BET surface area of 821 m² g⁻¹. This study showcases the utilisation of a solid-state synthetic route in accessing complex π-extended architectures and positions nitrogen-rich TNPs as versatile platforms for functional materials design.