Aggregation-induced emission sensors based on sulfide-containing naphthalimides for imaging latent fingerprints

Aggregation-induced emission luminogens have attracted extensive attention due to their wide applications. In this work, two naphthalimide derivatives (<bold>NIS1</bold> and <bold>NIS2</bold>) were designed and synthesized which could be used as the solid imaging agents for their AIE effects. In both molecules, V-shape structures were introduced to construct de-planar conjugated systems using O and N atoms as the centers. The center atoms tune the emissions of these molecules in deep blue (411 similar to 436 nm, <bold>NIS1</bold>) and yellow-green (521 similar to 540 nm, <bold>NIS2</bold>) regions in organic solvents with different polarity. <bold>NIS1</bold> and <bold>NIS2</bold> exhibit AIE-active fluorescence in their aqueous solutions (545 nm for <bold>NIS1</bold> and 600 nm for <bold>NIS2</bold>). Further studies on their photophysical properties indicate that the introduction of methylmercapto group (-SCH3) can enhance the AIE intensities compared to their mimic. DFT calculation was performed to explore the different transitions occurred in these compounds. At last, <bold>NIS1</bold> and <bold>NIS2</bold> were successfully fabricated as the solid imaging agents and applied to the latent fingerprints imaging on varied substances. A highlight in this work is these imaging agents can work well on the scene with high background fluorescence by optimizing the excitation wavelength and selecting suitable emission channel.