Cooperativity and Site-Selectivity of Intramolecular Hydrogen Bonds on the Fluorescence Quenching of Modified GFP Chromophores

meta-Fluorophores: an uncharted ocean of opportunities

meta-Fluorophores (MFs) are unique ultra-light (in terms of molecular weight (MW)) fluorophores exhibiting luminescence with a wide colour gamut ranging from blue to the NIR. Single benzenic MFs are easy to synthesize, are quite bright (with photoluminescence quantum yield (PLQY) as high as 63%) and exhibit very large Stokes shift (as high as 260 nm (8965 cm-1)), with large solvatochromic shift (as high as 175 nm), and very long excited-state-lifetime (as high as 26 ns) for such ultra-light fluorophores. An emission maximum of ≥600 nm has been achieved with an MF in a polar medium having a MW of only 177 g mol-1 and in a nonpolar medium having MW of only 255 g mol-1; therefore, a large-sized π-conjugated para-fluorophore is no longer a prerequisite for red/NIR emission. Structurally varied MFs pave the way for creating an ocean of opportunities and are thus promising for replacing para-fluorophores for different applications, ranging from bioimaging to LEDs.

Fluorescence Amplification of Unsaturated Oxazolones Using Palladium: Photophysical and Computational Studies

Weakly fluorescent (Z)-4-arylidene-5-(4H)-oxazolones (1), Φ_PL < 0.1%, containing a variety of conjugated aromatic fragments and/or charged arylidene moieties, have been orthopalladated by reaction with Pd(OAc)₂. The resulting dinuclear complexes (2) have the oxazolone ligands bonded as a C^N-chelate, restricting intramolecular motions involving the oxazolone. From 2, a variety of mononuclear derivatives, such as [Pd(C^N-oxazolone)(O₂CCF₃)(py)] (3), [Pd(C^N-oxazolone)(py)₂](ClO₄) (4), [Pd(C^N-oxazolone)(Cl)(py)] (5), and [Pd(C^N-oxazolone)(X)(NHC)] (6, 7), have been prepared and fully characterized. Most of complexes 3-6 are strongly fluorescent in solution in the range of wavelengths from green to yellow, with values of Φ_PL up to 28% (4h), which are among the highest values of quantum yield ever reported for organometallic Pd complexes with bidentate ligands. This means that the introduction of the Pd in the oxazolone scaffold produces in some cases an amplification of the fluorescence of several orders of magnitude from the free ligand 1 to complexes 3-6. Systematic variations of the substituents of the oxazolones and the ancillary ligands show that the wavelength of emission is tuned by the nature of the oxazolone, while the quantum yield is deeply influenced by the change of ligands. TD-DFT studies of complexes 3-6 show a direct correlation between the participation of the Pd orbitals in the HOMO and the loss of emission through non-radiative pathways. This model allows the understanding of the amplification of the fluorescence and the future rational design of new organopalladium systems with improved properties.

Solvatochromic Fluorescence of a GFP Chromophore-Containing Organogelator in Solutions and Organogels

Solvatofluorochromism, a solvation effect on the fluorescence color of an organic dye, is a property generally limited to fluid solutions. We demonstrate herein the concept of solid-state solvatofluorochromism by using an organogelator (1-SG), which consists of a solvatofluorochromic green fluorescence protein (GFP) chromophore (1) and a sugar gelator (SG). While 1-SG could be located in the liquid phase or in the fibrous solid matrix of the SG gel, our results show that the one in the solid matrix but near the liquid interface has superior fluorescence stability and quantum efficiency as well as solvatofluorochromicity than the one in the liquid phase. In addition, the phenomenon of fluorescence turn-on occurs when the gel is formed in protic solvents. These features have been applied to perform multicolor fluorescence patterning, chemical vapor sensing, data encryption and decryption, and real-time fluorescence cell imaging.

The effects of different heterocycles and solvents on the ESIPT mechanisms of three novel photoactive mono-formylated benzoxazole derivatives

The detailed effects of different heterocycles and solvents on the dynamical ESIPT mechanisms of three novel mono-formylated benzoxazole derivatives A–C in two different surroundings have been expounded by the TDDFT method at the B3LYP/TZVP level.

Exploring the ESIPT dynamical processes of two novel chromophores: symmetrical structure CHC and asymmetric structure CHN

The detailed ESIPT dynamical processes of CHC (symmetrical structure) and CHN (asymmetric structure) chromophores were revealed and compared using the TDDFT method at the B3LYP/6-31+G(d,p) level.