Increasing the stability of protein bioconjugates and improving the resolution of protein complexes is important for spectroscopic analysis in structural biology. The reaction of phenylsulfonated pyridine derivatives and protein thiols generates a stable, rigid and short thiolether tether, which is valuable in high-resolution spectroscopic measurements.

Novel dithienylethene derivatives with BF2-doped π-conjugation show efficient green light-excited photoswitching behaviors in solvents, PMMA film and living cells.

Site-specific labeling of proteins with lanthanide ions offers great opportunities for investigating the structure, function, and dynamics of proteins by virtue of the unique properties of lanthanides. Lanthanide-tagged proteins can be studied by NMR, X-ray, fluorescence, and EPR spectroscopy. However, the rigidity of a lanthanide tag in labeling of proteins plays a key role in the determination of protein structures and interactions. Pseudocontact shift (PCS) and paramagnetic relaxation enhancement (PRE) are valuable long-range structure restraints in structural-biology NMR spectroscopy. Generation of these paramagnetic restraints generally relies on site-specific tagging of the target proteins with paramagnetic species. To avoid nonspecific interaction between the target protein and paramagnetic tag and achieve reliable paramagnetic effects, the rigidity, stability, and size of lanthanide tag is highly important in paramagnetic labeling of proteins. Here 4'-mercapto-2,2':6',2''-terpyridine-6,6''-dicarboxylic acid (4MTDA) is introduced as a a rigid paramagnetic and fluorescent tag which can be site-specifically attached to a protein by formation of a disulfide bond. 4MTDA can be readily immobilized by coordination of the protein side chain to the lanthanide ion. Large PCSs and RDCs were observed for 4MTDA-tagged proteins in complexes with paramagnetic lanthanide ions. At an excitation wavelength of 340 nm, the complex formed by protein-4MTDA and Tb(3+) produces high fluorescence with the main emission at 545 nm. These interesting features of 4MTDA make it a very promising tag that can be exploited in NMR, fluorescence, and EPR spectroscopic studies on protein structure, interaction, and dynamics.

The development of novel solid-state fluorescence switches, particularly triggered by visible light, is of increasing interest for the potential application in optical data storage and super-resolution fluorescence microscopies. In this study, two carbazole–dithienylethene–BF2bdk triads CDB1 and CDB2, suspending carbazole and BF2bdk moieties on both sides of dithienylethene unit, have been developed. They exhibit blue-/NIR light-controlled photochromism with solvent-dependent characteristics. Moreover, CDB1 (o) reveals blue-/NIR light-induced reversible fluorescent switching behaviors in toluene, chloroform, poly­(methyl methacrylate) (PMMA) film, and powder state, while its analogue CDB2 (o) in the powder state exhibits no fluorescence due to a strong intermolecular π–π stacking interaction, and the fluorescent switching performance is observed only in toluene and PMMA film. The density functional theory calculations further validate the differences in their optical properties in the solution and powder states.