Boron Difluoride Curcuminoid Fluorophores with Enhanced Two-Photon Excited Fluorescence Emission and Versatile Living-Cell Imaging Properties.

The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a "cyanine-like" transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV-visible absorption and fluorescence spectra. Two-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photon absorption from the S0-S2 charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from a dipolar structure. Overall, this structure-relationship study allows the optimization of the two-photon brightness (i.e., 400-900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.

[Theory, principles and applications of fluorescent technologies in cellular biology and cancer research]. / Théorie, principes et applications des techniques de fluorescence en biologie cellulaire et cancérologie.

Using fluorescent technologies under the microscope is becoming unavoidable in biology research laboratories. These technologies, stemming from instrumental developments of biophysics, raised with the use of fluorescent proteins derived from the GFP (green fluorescent protein) as well as the market development of commercial instruments. They allow studying the dynamics of molecules of interests (FRAP, FCS...) as well as their interactions (FRET, FLIM...) on cells, cellular extracts or tissues. Unfortunately, these are often used without detailed knowledge of their principles as well as their theories. These aspects are developed and illustrated here through means of literature example.