Polyaryl substituted imidazobenzothiadiazoles as multifunctional organic fluorescent materials for visualization of latent fingerprints and lysosome staining

Organic fluorescent materials have attracted increasing attention for their applications in various fields. Design and synthesis of multifunctional organic fluorescent emitters based on simple molecular structure are still highly demanded and challenging. In this paper, we designed and synthesized six organic fluorescent molecules with polyaryl substituted imidazobenzothiadiazole structure. The substituents on imidazole ring have important effects on the optical properties. Compounds with N, N-dialkyl aniline moieties on imidazole ring could show obvious solvatochromic properties with relatively large Stokes shifts and low quantum yields. However, the fluorescent emissions of other compounds with phenol, 4-methoxy phenyl or methyl groups on imidazole ring are almost unaffected by the solvent polarity, and they can exhibit higher fluorescent quantum yields. Under acidic conditions, the fluorescence emission of these compounds can be gradually extinguished. In addition, the fluorescence emission can be recovered under basic conditions. Significant changes in fluorescence emission indicate that these molecules can be used as anti-counterfeiting inks. Further investigation showed that the compound with methyl group on imidazole ring can be used for latent fingerprint development. High-contrast fingerprint images are obtained on various substrate surfaces. It is also found that the compound with phenol moiety on imidazole ring can be utilized for lysosomes imaging in living cells accurately with high efficiency. This work provides a series of imidazobenzothiadiazole-based multifunctional organic materials with potential applications in security inks, latent fingerprint imaging and lysosome staining.