Monoaromatic molecules are a category of molecules containing a single aromatic ring which generally emit light in the ultraviolet (UV) region. Despite their facile preparation, the UV emission greatly limits their application as organic probes. In this study, we developed a general method to red shift the emission of monoaromatic molecules. Significant fluorescence red-shift (∼100 nm per intramolecular hydrogen bonding) can be achieved by introducing intramolecular hydrogen bonding units to benzene, a typical monoaromatic molecule. Upon increasing the number of hydrogen bonding units on the benzene ring, UV, blue, and green emissions are screened, which are switchable by simply breaking/restoration the intramolecular hydrogen bonding. As a demonstration, with the breaking of one intramolecular H-bonding, the green emission (λemmax = 533 nm) of 2,5-dihydroxyterephthalic acid (DHTA) changed to cyan (λemmax = 463 nm) upon the formation of its phosphorylated form (denoted as PDHTA), which, in the presence of alkaline phosphatase (ALP), hydrolyzed and recovered the green emission. By taking advantage of the switchable emission colors, ratiometric in vitro and endogenous ALP sensing was achieved. This general approach offers a great promise to develop organic probes with tunable emissions for fluorescence analysis and imaging by different intramolecular hydrogen bonding.

Somatic embryogenesis (SE) is one of the most promising processes for large-scale dissemination of elite varieties. However, for many plant species, optimizing SE protocols still relies on a trial-and-error approach. Using coffee as a model plant, we report here the first global analysis of metabolome and hormone dynamics aiming to unravel mechanisms regulating cell fate and totipotency. Sampling from leaf explant dedifferentiation until embryo development covered 15 key stages. An in-depth statistical analysis performed on 104 metabolites revealed that massive re-configuration of metabolic pathways induced SE. During initial dedifferentiation, a sharp decrease in phenolic compounds and caffeine levels was also observed while auxins, cytokinins and ethylene levels were at their highest. Totipotency reached its highest expression during the callus stages when a shut-off in hormonal and metabolic pathways related to sugar and energetic substance hydrolysis was evidenced. Abscisic acid, leucine, maltotriose, myo-inositol, proline, tricarboxylic acid cycle metabolites and zeatin appeared as key metabolic markers of the embryogenic capacity. Combining metabolomics with multiphoton microscopy led to the identification of chlorogenic acids as markers of embryo redifferentiation. The present analysis shows that metabolite fingerprints are signatures of cell fate and represent a starting point for optimizing SE protocols in a rational way.