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Two new Δ1-pyrroline ligands and their corresponding boron complexes have been synthesized and characterized. Their luminescent properties were investigated, the boron complexes emitting brightly around 410 nm. The presence of the exocyclic double bond has no influence on their electronic properties, meaning that this part of the complex could be used to fine tune their properties without disturbing their fluorescence. [ABSTRACT FROM AUTHOR]

Difluoroborates complexes based on 2′-hydroxyphenones were synthetized and their optoelectronic properties studied in both solution and solid state. These new dyes exhibit fluorescence emission in the visible region at similar wavelengths, intriguingly with higher quantum yields in the solid state than in solution. The enhanced emission in the solid state is rationalized on the basis of the crystal structure of the dyes. Image 1 • The synthesis of five boron complexes based on 2′-hydroxyphenone ligands is presented. • They are weakly emissive in solution. • Their emission intensity increases upon crystallization. • Changing the substituents tunes their absorption and emission spectra. [ABSTRACT FROM AUTHOR]

A simple methodology giving rise to a new series of isatin-porphyrin conjugates and corresponding intracyclized derivatives is described. Palladium-catalyzed amination reactions of iodinated isatin derivatives containing the 3-carbonyl group protected with ketal functionalities and 2-amino-5,10,15,20-tetraphenylporphyrinatonickel(II) was the used procedure. The combination of palladium catalysts and the phosphine ligand dicyclohexylphospino-2′,4′,6’-triisopropylbiphenyl (XPhos) led to isatin-porphyrin conjugates in good yields. Nevertheless, the use of palladium acetate even resulted on the formation of additional six membered fused ring compounds. This brings a new perspective to access quinolino[2,3,4- at ]porphyrins, a set of compounds which are typically obtained by harsh Cadogan or thermal cyclization approaches. [ABSTRACT FROM AUTHOR]

Conjugates based on porphyrin (porph) and rhodamine (rh) moieties linked by amide bonds, dyad 1 (porph-spacer-rh) and triad 2 (porph-spacer-rh-spacer-porph), were prepared respectively from precursor 1 and precursor 2 . The sensing ability of precursor 1 , dyad 1 and triad 2 towards the divalent metal ions Cu 2+ , Zn 2+ , Cd 2+ , Pb 2+ , Hg 2+ and the monovalent Hg + was explored in solution by absorption and fluorescence spectroscopy as well as in gas phase using matrix-assisted laser desorption/ionization (MALDI)-TOF mass spectrometry. In solution one-metal-per-ligand molar ratio was obtained with precursor 1 and triad 2 , however, a two-metal-per-ligand molar ratio was observed with dyad 1 . Additionally, the results obtained by MALDI-TOF-MS confirmed the gas-phase sensing abilities of dyad 1 towards all metal ions tested and of triad 2 towards Zn 2+ . Computational DFT calculations confirm the same stoichiometry. [ABSTRACT FROM AUTHOR]

In this paper, a novel family of (E , E)-aminoaurone-type compounds with an extended π-system has been developed, prepared via copper catalysed aza-Michael addition, ring opening, and cyclization between (E)-3-bromo-2-styrylchromones and aniline derivatives in the presence of base under mild reaction conditions. All derivatives showed strong solvatochromic absorption and emission properties, which make them potential compounds for sensing applications. The presence of electron-withdrawing substituents in the aromatic ring had a strong influence on the fluorescence behavior of the aurone-type derivatives. In particular, aurone 3h has promising characteristics, not only for the large Stokes observed, but also for the presence of the C -glycosyl moiety. We conclude that appropriately substituted π-extended aminoaurones are potentially useful as biological probes. • A copper-catalysed one-pot cascade between (E)-3-bromo-2-styrylchromones and anilines has been developed. • This methodology allows the stereoselective synthesis of (E , E)-aminated aurone derivatives with a vinylogous extension. • This new family of aurone-type derivatives display strong solvatochromic absorption and emission properties. • The optical properties of aurone-type derivatives may be tuned for a particular application by functional group selection. [ABSTRACT FROM AUTHOR]

Usually, chalcones are not luminescent, although their derivatives with push-pull patterns of substitution may present fair quantum yields. Intramolecular hydrogen bonding between a hydrogen donor (–OH or –NH) and the chalcone carbonyl promotes Excited State Intramolecular Proton Transfer (ESIPT). If the dye is fluorescent, the emission can derive from one of the excited tautomers, or from both and in this case a dual emission is observed. Here, 2′-aminochalcones with a strong push-pull character, incorporating electron-donating groups on one side, and electron-withdrawing groups on the amine, present dual emission ascribed to ESIPT between the keto-enamine and the enol-imine tautomers. The hydrogen bonds strength was studied by NMR and DFT calculations. A correlation between the tautomerization energy gap and the hydrogen bond strength was observed, depending on the electron donating or electron withdrawing group on the amine. The electron withdrawing groups bonded to the proton donor have little influence on the quantum yield and emission wavelength. In contrast, the electron donating groups connected to the proton acceptor have a significant effect on the quantum yield and induce an absorption and emission red shift. Pushing and pulling on both sides of an intramolecular hydrogen bond can modulate the excited-state intramolecular proton transfer, and therefore the emission profile of a fluorophore. But here, pushing is more rewarding than pulling. [Display omitted] • Push-pull fluorophores presenting an intramolecular hydrogen bond were synthesized. • Excited-state Intramolecular Proton Transfer is witnessed by the double emission. • Changing the pushing and pulling groups influence the double emission profile. • The double emission profile was rationalized using DFT calculations. [ABSTRACT FROM AUTHOR]

The green fluorescent protein (GFP) is extensively used as a biomarker for fluorescence biological imaging. The chromophore in GFP is only fluorescent when confined into the β–barrel of the protein. Similarly, synthetic analogues of the fluorophore of GFP are usually non-emissive in solution, due to free rotation around the aryl-alkene bond and (Z / E)-isomerization of the double bond. Here, the synthesis and characterization of three analogues of the fluorophore of GFP are reported. The introduction of more electron donating substituents induces a red-shift in the absorption and emission. The fluorophores are more emissive in the solid state than in solution, and a study of their crystal structure reveals that the (Z / E)-isomerization is efficiently blocked in the crystals. Image 1 • A new synthesis of analogues of the Green Fluorescent Protein fluorophore is presented. • They are almost non emissive in solution. • Their emission intensity increases up to a hundred times upon crystallization. • Changing the substituents tunes their absorption and emission spectra. [ABSTRACT FROM AUTHOR]