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Steady-state and time-resolved techniques were employed to study the excited-state proton-transfer (ESPT) rate of two newly synthesized photoacids – quinone cyanine diindolium (QCy7) and its dipicolinium analog (QCy9) – in three protic solvents, water, methanol and ethanol. The ESPT rate constant k PT of QCy7, whose pKa*∼−6.5 in water, methanol and ethanol is 1.2×10 13 s −1 ...
The firefly oxyluciferin family of fluorophores has been attracting attention from the research community, due to their role on firefly bioluminescence. Moreover, this family exhibits a very efficient fluorescence quenching process. The elucidation of this process is very important, as it may occur inside of the luciferase active site, thereby decreasing the life time of bioluminescence. To this end...
Steady-state and time-resolved emission spectra were measured to study the relaxation of all-trans retinoic acid (ATRA) from its excited-states in a number of solvents. We found that the time-resolved emission signal is composed of three decay components arising from three different excited-states. The ultrafast component that is shorter than 80fs is dominant at λ≤500nm, whereas the intermediate component...
The photoprotolytic properties of a recently synthesized photoacid, hydroxycoumarin-dipicolinium salt (HCD) were studied by means of time-resolved emission techniques. We found that HCD is a super-photoacid with pKa*<−2 and with an excited-state proton transfer to water with a rate constant of kPT=1.4×1011 s−1. We also found that HCD undergoes ESPT in a large number of protic solvents. The kinetic...
Time-resolved emission techniques were employed to study the pressure effect on curcumin's luminescence in several aliphatic alcohols. We found that the hydrostatic pressure of up to 2GPa affects the decay rate of curcumin emission in the same way it affects the protonated form of many photoacids. We therefore propose that curcumin, which has two phenol groups, is a strong photoacid. Strong photoacids...
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