Boosting The Solid‐State Luminescence of Phenazine Derivatives by Enhancing Intermolecular Hydrogen Bonds and π–π Interactions in Cocrystals

Six monosubstituted phenazine derivatives were designed and synthesized for constructing cocrystals to investigate their structure-property relationship. It was found that 2-substituted phenazines could form cocrystals with 2,6-dimethylphenylboronic acid (DBA). These cocrystals exhibited red-shifted and enhanced luminescence relative to their individual components, especially 2NP-DBA whose luminescence efficiency was nearly 100 times higher than that of 2NP. By analyzing the single-crystal structures of the cocrystals and their components, enhanced hydrogen bonds and π-π interactions between molecules were detected in cocrystals, which suppressed the nonradiative transition pathways. Consequently, all three cocrystals demonstrated enhanced luminescence with strong continuous π-π interactions, which differed from the previously reported luminescence enhancement resulting from the destruction of π-π interactions. An in-depth investigation of these cocrystals can not only provide a better understanding of the structure-property relationship of organic luminescent materials, but also help develop organic luminescent materials with intense solid-state luminescence and strong π-π interactions. In addition, the optical response of these cocrystals to acidic vapors has been successfully applied in anti-counterfeiting.