A Facile Synthetic Method and New Derivatives of Phthalorubines

Phthalorubines (Prs), a new series of fused-ring dyes, with novel planar structure, interesting synthetic mechanism, characteristic spectra properties and multiple coordinated patterns, have potential applications in different fields.During the start-up stage for phthalorubine research, a molecule without any substituents, such as Pr-2, is the most important compound for both synthetic studies and application exploration.Reported method to obtain Pr-2 is via decyanation of Pr-1, the first phthalorubine compound easily synthesized from phthalonitrile.However, the process of decyanation requires expensive Rh(I) complex as catalyst, which also make the reaction difficult to amplify.These disadvantages greatly limit follow-up studies of phthalorubines.A facile method to synthesize Pr-2 could effectively accelerate the development and subsequent studies of phthalorubines.Herein, we reported a facile method to synthesize Pr-2 via Ni(II) catalyzed process with high yield of 58%, while this method could be amplified to more than 10 grams.Moreover, during the process of tuning reaction conditions, two new kinds of phthalorubines were detected, with cyano group (Pr-1.5)and methyl group (Pr-1.6),respectively.According to the results of different conditions, Pr-1.5 is the key intermediate product from Pr-1 to Pr-2.Methyl group in molecule Pr-1.6 is derived from trimethylaluminum, which also works as Lewis acid in the process of decyanation.The structures of Pr-1.5 and Pr-1.6 were further confirmed by X-ray single crystal diffraction, exhibiting planar structures with strong π-π interaction.In addition, different substituents greatly influence the packing patterns of phthalorubines, while molecules Pr-1.5 pack as "head-tail" pattern and Pr-1.6 as "head-head" pattern.We also studied the photophysical properties of these two new phthalorubines.Pr-1.5 and Pr-1.6 exhibit similar absorption spectra to reported compounds but totally different emission efficiencies.It suggests electron donating groups is beneficial to high quantum yield.The facile synthetic method and properties reported in this work would greatly help the development of phthalorubines.