Constructing Dual-State Emissive Fluorophores via Boc Protection and Discovering a High-Fidelity Imaging Probe for Lipid Droplets

Dual-state emissive (DSE) materials exhibit fluorescence in both solid and solution states and have become an emerging material in the fields of materials science and sensing in recent years. However, due to the lack of effective and universal preparation methods, DSE materials, especially those with long emission wavelengths, are still scarce. Developing an effective method for constructing such DSE molecules is urgently needed. In this study, we constructed three DSE molecules (NRP-Boc, DCIP-Boc, and DCMP-Boc) with far-red to near-infrared fluorescence by simply modifying three traditional aggregation-caused quenching (ACQ) fluorophores with tert-butyloxycarbonyl (Boc) groups. Density functional theory (DFT) calculations and crystal data revealed the reasons for the bright fluorescence of these three molecules in solution and solid, demonstrating that this Boc protection method is a simple and effective strategy for constructing DSE molecules. We also found that these three DSE molecules have the potential to target and visualize lipid droplets (LDs). Among them, DCIP-Boc shows advantages of a large Stokes shift, long emission wavelength, low fluorescence background, and good photostability in cells, providing a powerful new molecular tool with DSE property for high-fidelity imaging of LDs.