Fluorescent Proton Sensors Based on Energy Transfer

Abstract

Photophysical data and orbital energy levels (from electrochemistry) were compared for molecules with the same BODIPY acceptor part (red) and perpendicularly oriented xanthene or BODIPY donor fragments (green). Transfer of energy, hence the photophysical properties of the cassettes, including the pH dependant fluorescence in the xanthene containing molecules, correlates with the relative energies of the frontier orbitals in these systems. Intracellular sensing of protons is often achieved via sensors that switch off completely at certain pH values, but probes of this type are not easy to locate inside cells in their “off-state”. A communication from these laboratories (J. Am. Chem. Soc., 2009, 131, 1642 – 3) described how the energy transfer cassette 1 could be used for intracellular imaging of pH. This probe is fluorescent whatever the pH, but its exact photophysical properties are governed by the protonation-states of the xanthene donors. This work was undertaken to further investigate correlations between structure, photophysical properties, and pH for energy transfer cassettes. To achieve this, three other cassettes 2 – 4 were prepared another one containing pH-sensitive xanthene donors (2), and two “control cassettes” that each have two BODIPY-based donors (3 and 4). Both the cassettes 1 and 2 with xanthene-based donors fluoresce red under slightly acidic conditions (pH < ca 6), and green when the medium is more basic (> ca 7), whereas the corresponding cassettes with BODIPY donors give almost complete energy transfer regardless of pH. The cassettes that have BODIPY donors by contrast, show no significant fluorescence from the donor parts, but the overall quantum yields of the cassettes when excited at the donor (observation of acceptor fluorescence) are high (ca 0.6 and 0.9). Electrochemical measurements were performed to elucidate orbital energy level differences between the pH-fluorescence profiles of cassettes with xanthene donors, relative to the two with BODIPY donors. These studies confirm energy transfer in the cassettes is dramatically altered by analytes that perturb relative orbital levels. Energy transfer cassettes with distinct fluorescent donor and acceptor units provide a new, and potentially useful, approach to sensors for biomedical applications.

Spectroscopic and In Vitro Investigations of Boron(III) Complex with Meso-4-Methoxycarbonylpropylsubstituted Dipyrromethene for Fluorescence Bioimaging Applications

“…The electronic absorption spectrum of [BF 2 L] has a typical two-band form, in which the high-intensity S 0 → S 1 band has a maximum at the wavelength of 498–503 nm and a shoulder on the left slope at 471–476 nm, and the broadened less intense S 0 → S 2 band was observed in the shorter wavelength region at λ = 358–364 nm ( Table 1 , Figure 2 ). The values of the extinction coefficients ( ε ) of the first intense band are high enough and range from ~56,000 to 73,000 L·mol −1 ·cm −1 ( Table 1 ) and are comparable with those for other meso -substituted BODIPYs [ 12 , 17 , 18 ]. The synthesized complex intensively fluoresces in the blue-green region of the spectrum.…”

Synthesis of BODIPY dyes through postfunctionalization of the boron dipyrromethene core

“…164 Suzuki, Heck and Sonogashira reactions have all been reported with 2,6-dihalogenated BODIPYs. [171][172][173][174][175]189,190 Scheme 38: Halogenation of BODIPY followed by functionalization though Pd-catalyzed cross-coupling reactions.…”

Highly sensitive and selective Hg2+-chemosensor based on dithia-cyclic fluorescein for optical and visual-eye detections in aqueous buffer solution

“…Fluorescent sensor was an interesting alternative technique for qualitative and quantitative analyses of many analytes, such as protons, small molecules, anions or cations, including Hg 2+ [9][10][11][12]. This method was well-known for high sensitivity, high selectivity, inexpensive cost and rapid response, and could be applied for on-site detection of heavy metal ions [13][14][15][16].…”