A Greener Route to Blue: Solid‐State Synthesis of Phthalocyanines

Phthalocyanines are important organic dyes with a broad applicability in optoelectronics, catalysis, sensing and nanomedicine. Currently, phthalocyanines are synthetized in high boiling organic solvents, like dimethylaminoethanol (DMAE), which is a flammable, corrosive, and bioactive substance, miscible with water and harmful to the environment. Here we show a new solid‐state approach for the high‐yielding synthesis of phthalocyanines, which reduces up to 100‐fold the amount of DMAE. Through systematic screening of solid‐state reaction parameters, carried out by ball‐milling and aging, we reveal the influence of key variables—temperature, presence of a template, and the amount and role of DMAE in the conversion of tBu phthalonitrile to tetra‐tBu phthalocyanine. These results set the foundations to synthesize these high‐performance dyes through a greener approach, opening the field of solid‐state synthesis to a wider family of phthalocyanines. In this manuscript, the first high‐yielding solid‐state synthesis of a phthalocyanine dye is shown. These organic dyes are broadly applicable, while the inherent low solubility has so far challenged the sustainability of their synthesis. The developed solid‐state approach for the synthesis of tBu‐phthalocyanine in catalytic amounts of dimethylaminoethanol, avoids bulk solvents and harsh temperatures, while achieving excellent yields.