Compound 1 was designed and synthesized as a new fluorescent thiol probe. Probe 1 was constructed on the basis of the conjugate 1,4-addition of thiols to alpha,beta-unsaturated ketones. Notably, probe 1 has suitable water solubility, which allows the sensing assay to be performed in water. Probe 1 is highly sensitive for thiols with a 211-fold fluorescence dynamic range and a low detection limit of 9.25x10(-7) M. The major features of probe 1 also include a high selectivity for thiols over other relevant biological species, excitation and emission in the visible region, rapid functioning at pH 7.4, and a good linear relationship between the fluorescence signal and the thiol concentration. Accordingly, these desirable characteristics may render probe 1 as potentially useful for biological applications.

Small-molecule organic dyes have been widely used in fluorescent probes, [1] labels, [2] logic gates, [3] light-emitting materials, [4] and light-harvesting systems. [5] However, the undesirable photophysical properties of various fluorophores still constrain the full potential of their applications. For instance, many bright organic dyes including rhodamine, fluorescein, boron dipyrromethane (BODIPY), and cyanine derivatives have the serious disadvantage of very small Stokes shifts (typically less than 25 nm), which can lead to serious self-quenching and fluorescence detection errors because of excitation backscattering effects.[6] Therefore, there is a need to develop dyes with improved properties.Since it is still difficult to judiciously design single organic dyes with desirable photophysical properties, considerable attention has recently been paid to the exploration of multifluorophores with energy-donor-acceptor architectures. [1m, 6b, 7-9] In this regard, some energy-donor-acceptor systems based on fluorescence resonance energy transfer (FRET) have been constructed. [6b, 8] FRET dyads are usually linked by a nonconjugated spacer, and the energy transfer occurs through space. Although the pseudo-Stokes shifts (the wavelength discrepancy between the donor absorption and the acceptor emission in an energy transfer system with almost 100 % energy transfer efficiency [7] ) of FRET-based energy cassettes are larger than the Stokes shifts of either the donor or acceptor dyes, FRET-based cassettes are still limited by the requirement that the donor emission must have strong overlap with the acceptor absorption.[10] This requirement essentially restricts the pseudo-Stokes shifts as well as the emission shifts (the emission wavelength shift between the donor and acceptor) of FRET-based systems. Like the pseudo-Stokes shift, the emission shift is also an important parameter in energy-transfer dyads. A large emission shift in energy transfer systems should result in two well-separated emission peaks, which is favorable for the precise measurement of the peak intensities and ratios.[6b, 11] Thus, energytransfer dyads with large pseudo-Stokes shifts and emission shifts are desirable.By contrast, through-bond energy transfer (TBET) is theoretically not subjected to the constraint of intense spectral overlap between the donor emission and the acceptor absorption.[9] Thus, TBET cassettes may have large pseudoStokes shifts and emission shifts. Unlike through-space energy-transfer cassettes, in TBET cassettes, the donor and the acceptor units are joined by a conjugated spacer. Burgess and co-workers have developed elegant TBET systems based on the conjugated fluorescein-rhodamine system. [9a,b] However, the fluorescein (donor) emission overlaps significantly with the rhodamine (acceptor) absorption and the advantage of TBET, that is, no requirement of strong spectral overlap between the donor emission and the acceptor absorption, was not really capitalized upon in these conjugated fluoresceinrhodamine energy transfer ...

A novel strategy to systematically tune the pK(a) values of rhodamines is described. This strategy was applied to rationally develop compound 1e with a pK(a) of 6.5, the highest among rhodamine amide derivatives, and it could be employed to detect acidic pH variations in living cells with a turn-on signal.

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Coumarin pyridyl ketone 1 was designed and synthesized as a new chromogenic sensor for transition-metal ions. Remarkably, the chemosensor showed ion discrimination by exhibiting different extents of bathochromic shifts: 118 nm for Cu . This ion-dependent redshift in the visible region allows the selective detection of these three transition-metal ions by the naked eye. Studies