Multifunctional behavior of bis-acylhydrazone: Real-time detection of moisture in organic solvents, halochromism and aggregation induced emission

A versatile novel indenopyrazine/indenoquinoxaline appended acylhydrazones (1 and 2) have been designed and synthesized successfully. Compounds 1 and 2 are designed such that, it comprises of acylhydrazone, which is responsible for moisture detection via deprotonation of the original molecule, pyrazine, pyridine and hydrazone unit which is responsible for halochromism via protonation and deprotonation, further the integrated twisted molecular structure results in the aggregation-induced emission features. Successive treatment of F- and moisture to compound 1 and 2 produce reversible colorimetric responses that are easily visualized by the naked eye. Further, the corresponding mechanism was effectively confirmed by H-1 NMR spectral analysis. The inherent halochromic features of appended unique pyrazine and pyridine core in compounds 1 and 2 were studied by the sequential addition of trifluoroacetic acid (TFA) and triethylamine (TEA) which is authenticated by reversible colorimetric changes as well as absorption spectral studies. Compound 1 adopts a twisted scissor-like structure and due to multiple weak interactions results in an interesting supramolecular network. Furthermore, both compound 1 and 2 exhibits the aggregation-induced emission features in DMF/water mixture, which was expansively confirmed through DLS particle analysis and TEM images. The integration of three distinct features into a single molecule are scarce.

Automated summary

A versatile novel indenopyrazine/indenoquinoxaline appended acylhydrazones have been successfully designed and synthesized, which exhibit moisture detection, halochromism, and aggregation-induced emission features. Reversible colorimetric responses were observed in response to F- and moisture, with the mechanism confirmed by H-1 NMR spectral analysis. The integration of these distinct features into a single molecule is rare, showcasing a unique supramolecular network structure.