Tailoring the positive and negative solvatochromism for chalcone analogues to detect heterozygous protein co-aggregation

Simple cyclic chalcone dye with multiple optical functions: Piezochromism and lysosomes staining

Both artificially synthesized and naturally occurring cyclic chalcones have been widely studied for their excellent biological activities. However, research on its photophysical properties is still limited. In the present study, we designed and synthesized a small molecule fluorescent dye based on the ICT effect, using dimethylamino as the electron-donating group and carbonyl as the electron withdrawing group, and investigated its photophysical properties in depth. Although YB is a simple small molecule, it exhibits significant piezochromic properties. The fluorescence of YB can change from green to yellow through grinding. After solvent fumigation, the fluorescence reverts to green. Furthermore, YB was used successfully in the lysosomal targeting. This study expands the research on the photophysical properties of cyclic chalcone and give richness to application of cyclic chalcone compounds.

Developing NIR xanthene-chalcone fluorophores with large Stokes shifts for fluorescence imaging

A series of novel near-infrared (NIR) xanthene-chalcone fluorophores were constructed through a modular synthesis with the electron-donating xanthene moiety and the electron-withdrawing chalcone moiety. These fluorophores are convenient for fluorescence imaging in living cells, benefiting from their NIR emissions (650-710 nm), large Stokes shifts (>100 nm), moderate quantum yields and low cytotoxicity. The substituted hydroxyl group of the xanthene-chalcone fluorophore HCA-E facilitates the development of multifunctional fluorescent probes. As an example, a highly sensitive and selective probe N-HCA-E for glutathione (GSH) detection was developed based on the fluorophore HCA-E. A 4-nitrobenzenesulfonyl (4-Ns) group was introduced to cage the hydroxyl group of HCA-E, which was used as a selective recognition site for the thiol of GSH and an effective fluorescence quencher. Probe N-HCA-E revealed NIR "turn-on" fluorescence (709 nm) for endogenous and exogenous GSH detection in lysosomes with a large Stokes shift (129 nm) and high anti-interference ability.

Solvatochromism of new tetraphenylethene luminogens: integration of aggregation-induced emission and conjugation-induced rigidity for emitting strongly in both solid and solution state

In this study, we synthesized and characterized four tetraphenylethene (TPE) analogs, investigated their photophysical properties, and conducted quantum chemical calculations. Some molecules exhibited aggregation-induced emission enhancement behavior and showed efficient emission in both solid and solution states. Solvatochromism was observed in particular derivatives, with solvent polarity influencing either a bathochromic or hypsochromic shift, indicating the occurrence of photoinduced intramolecular charge transfer (ICT) processes. Quantum chemical calculations confirmed that variations in molecular packing and rigidity among the TPE analogs contributed to their diverse behavior. The study showcases aggregation in luminophores without significant impact on the excited state and highlights how minor alterations in terminal substituents can lead to unconventional behavior. These findings have implications for the development of luminescent materials. Furthermore, the synthesized compounds exhibited biocompatibility, suggesting their potential for cell imaging applications.

Coumarin-Conjugated Macromolecular Probe for Sequential Stimuli-Mediated Activation

Protein bioconjugation has emerged as one of the most valuable tools for the development of protein-based biochemical assays. Here, we report a fluorescent macromolecular material, RF16_Halo, in which the coumarin derivative RF16 is specifically conjugated onto HaloTag protein to achieve a dual-stimuli-mediated fluorescence response. RF16 is first obtained by installing a H2O2-sensitive boron cage onto the C7 hydroxy moiety of the coumarin fluorophore with a HaloTag ligand attaching to the pH-labile 1,3-dioxane moiety. Upon stimulation, RF16_Halo exhibits a sequential fluorescence response to H2O2/pH at both liquid and solid interfaces. The fluorescence of the RF16_Halo-based protein film increases linearly toward H2O2 with a higher sensitivity when compared with that of RF16. Subsequently, the H2O2-cleaved RF16_Halo presents a pH-dependent fluorescence decrease under acidic conditions. Such a stimulus-responsive fluorescence "off-on-off" multimode enables RF16_Halo to be applied as a sequential logic circuit. In addition, we evaluate the fluorescence labeling ability of RF16 to intracellular IRE1_Halo protein and demonstrate that RF16 containing the HaloTag ligand could be precisely retained in cells to track IRE1_Halo protein. Hence, we provide a unique structural design strategy to construct a fluorescence dual-responsive macromolecular probe for information encryption and protein tracking in cells.

Construction of Coumarin-Based Bioorthogonal Macromolecular Probes for Photoactivation

Photoactivatable fluorescence imaging is one of the most valuable methods for visualizing protein localization, trafficking, and interactions. Here, we designed four bioorthogonal fluorescent probes K1-K4 by installing photoactive cages and HaloTag ligands onto the different positions of the coumarin fluorophore. Although K1-K4 all exhibited rapid photostimulated responses in aqueous solution, only K3 was found to have an obvious aggregation-induced emission (AIE). Next, macromolecular fluorescent probes Kn=1/2/3/4_POIs were obtained by covalently attaching K1-K4 to HaloTag-fused proteins of interest (POIs). Kn=3/4_POIs exhibited a higher fluorescence increase than that of Kn=1/2_POIs upon photoactivation in both liquid and solid phases. Moreover, K3_GFP_Halo and K4_GFP_Halo presented the fluorescence resonance energy transfer (FRET) from photocleaved K3 and K4 to GFP in the protein complex. We further examined the fluorescence labeling ability of K1-K4 to intracellular IRE1_Halo protein and found that K3 and K4 containing the HaloTag ligand on the C4 position of coumarin could be retained in cells for long-term tracking of the IRE1_Halo protein. Hence, we established a platform of novel bioorthogonal fluorescent probes conjugating onto Halo-tagged POIs for rapid photoactivation in vitro and in cells.