Ultrafast Excited-State Proton Transfer to the Solvent Occurs on a Hundred-Femtosecond Time-Scale

Steady-state and ultrafast time-resolved techniques were used to study a newly synthesized photoacid, phenol-carboxyether dipicolinium cyanine dye, QCy9. We found that the excited-state proton transfer (ESPT) to water occurs at the remarkably short time of about 100 fs, <i>k</i>_PT ≈ 1 × 10¹³ s^–1, the fastest rate reported up to now. On the basis of the Förster-cycle, the p<i>K</i>_a* value is estimated to be −8.5 ± 0.4. In previous studies, we reported the photoacidity of another superphotoacid, the QCy7 for which we found an ESPT rate constant of ∼1.25 × 10¹² s^–1, one-eighth that of the QCy9 compound. We found a kinetic isotope effect of the ESPT of about two

“Donor–Two-Acceptor” Dye Design: A Distinct Gateway to NIR Fluorescence

The detection of chemical or biological analytes upon molecular reactions relies increasingly on fluorescence methods, and there is a demand for more sensitive, more specific, and more versatile fluorescent molecules. We have designed long wavelength fluorogenic probes with a turn-ON mechanism based on a donor–two-acceptor π-electron system that can undergo an internal charge transfer to form new fluorochromes with longer π-electron systems. Several latent donors and multiple acceptor molecules were incorporated into the probe modular structure to generate versatile dye compounds. This new library of dyes had fluorescence emission in the near-infrared (NIR) region. Computational studies reproduced the observed experimental trends well and suggest factors responsible for high fluorescence of the donor–two-acceptor active form and the low fluorescence observed from the latent form. Confocal images of HeLa cells indicate a lysosomal penetration pathway of a selected dye. The ability of these dyes to emit NIR fluorescence through a turn-ON activation mechanism makes them promising candidate probes for <i>in vivo</i> imaging applications

Synthesis, Characterization, and Reactivity of Thermally Stable Anhydrous Quaternary Ammonium Fluorides

The synthesis and properties of a new class of anhydrous quaternary ammonium fluorides, based on the rigid skeleton azabicyclo[2.2.2]­octane, is described. Compounds <b>2a</b>–<b>d</b> were easily prepared by passing the corresponding ammonium iodides over fluoride-based resin followed by drying their hydrated form at 100 or 140 °C under reduced pressure. The stability (experimental and theoretical study), solubility, reactivity, and characterization by solution and solid-state MAS NMR are discussed

Ultrafast Excited-State Intermolecular Proton Transfer of Cyanine Fluorochrome Dyes

Steady-state and time-resolved emission spectroscopy techniques were employed to study the excited-state proton transfer (ESPT) to water and D₂O from QCy7, a recently synthesized near-infrared (NIR)-emissive dye with a fluorescence band maximum at 700 nm. We found that the ESPT rate constant, <i>k</i>_PT, of QCy7 excited from its protonated form, ROH, is ∼1.5 × 10¹² s^–1. This is the highest ever reported value in the literature thus far, and it is comparable to the reciprocal of the longest solvation dynamics time component in water, τ_S = 0.8 ps. We found a kinetic isotope effect (KIE) on the ESPT rate of ∼1.7. This value is lower than that of weaker photoacids, which usually have KIE value of ∼3, but comparable to the KIE on proton diffusion in water of ∼1.45, for which the average time of proton transfer between adjacent water molecules is similar to that of QCy7