•The probe works at near-infrared light regions.•The probe functions as an “off-on” sensor for S2−.•The detection limit for S2− is 0.15 μM.Sulfide plays distinct roles in biological systems. More sensitive probes are essential for the fluorescent detection of S2−. The NIR probe IR800-DPII, which has been synthesized based on heptamethine cyanine and NBD, is able to function as an “off-on” fluorescence sensor for detecting S2− through substrate-induced cleavage mechanism.

The macromolecule, PPV-NMe3+-DO3A-Gd, in which paramagnetic DO3A-Gd units were introduced into a fluorescent polymer PPV-NMe3+, was synthesized. It inherited the fluorescent properties of PPV-NMe3+ and gained the magnetic relaxivity of DO3A-Gd. PPV-NMe3+-DO3A-Gd was potential to function as a fluorescent/MRI dual-modal contrast agent.The instructions of the box below: The side chains of the fluorescent conjugated polymer PPV-NMe3+ were modified with 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7-triacetic acid gadolinium chelate (DO3A-Gd) units through ‘Cu (I)-catalyzed azide-Alkyne Cycloaddition (CuAAC)’ reactions, which a kind of ‘click reaction’. The final product, PPV-NMe3+-DO3A-Gd, can achieve dual-modal Fluorescent/MR imaging.

A synthesized blue fluorescent protein (BFP) chromophore analogue 2-BFP ((4Z)-4-[(1H-imidazol-2-yl)methylene]-1-methyl-2-phenyl-1H-imidazol-5(4H)-one) displays dual fluorescent emission that arises from the same Z-isomer. The larger Stokes shift emission is a result of excited-state intramolecular proton transfer (ESIPT) mediated by an N–H···N type of hydrogen bond. Compared to other green fluorescent protein (GFP) analogues with ESIPT such as o-HBDI, 2-BFP possesses greatly enhanced quantum yields and much slower proton-transfer rates. In addition, fluorescence up-conversion experiments revealed two rising components of lifetime for the tautomer formation of 2-BFP. The results imply that the relaxation of the N* state in 2-BFP triggers the proton transfer of the molecule. The weaker photoacidity of N–H is proposed to be crucial for these photophysical and photochemical properties. Finally, the ESIPT process in 2-BFP is inhibited in protic solvents (MeOH) or by the formation of metal–chelate complexes, providing insights for further developments and applications of ESIPT molecules.Keywords: dual fluorescent emission; excited-state intramolecular proton transfer; fluorescence quantum yield; fluorescence up-conversion; green fluorescent protein; proton-transfer rate;