Excited-state acidity pyranine

If pK is less than - 2, the acid is very strong in the excited state and, in general, ki is much larger than the reciprocal of the excited-state lifetime, so that the fluorescence of the acidic form is not observed at pH > pK + 2 but only for lower pH values (Figure 4.10B). Eqs (4.55) and (4.56) expressing the pH dependence of Iha and Ia account for the shape of the curves. However, this is not strictly valid when geminate recombination occurs. A weak emission of the acidic form can then be observed. This is the case for pyranine (pK = 7.7, pK = 1.3) (Figure 4.11). 

As expected, water pool microviscosity decreased and micropolarity increases as Wq increases. With some probes, bulk water values are not obtained until Wq is much greater than 10 these may be cases where the probe reports on interfacial water as well as on the free bulk water in the pool. Indeed, the fluorescence polarization measurements of Zinsli [55] using l-amino-naphthalene-4-sulfonic acid (a water pool probe) and 2-(N-tetradecyl)amino-naphthalene-6-sulfonic acid (an interfacial probe) and the pKa measurements of Sunamoto and co-workers [56] on excited state pyranine have been interpreted in terms of a radially inhomogeneous microviscosity and micropolarity, with a viscous boundary layer of hydration water (type I) at the pool periphery and an inner core of water (type II) whose properties rapidly approach those of ordinary bulk water as Wq increases. 

Pyranin and Prodan. Water consumption was probed during the early stage of the sol-gel reaction of TMOS by using excited state proton transfer of PYRANIN (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt Fig. 20-8) (Kaufman, 1988). This PYRANIN was applied to study aminosilicate matrix (Pouxviel, 1989) and as an in situ fluorescence... 

Kondo, H. Miwa, L Sunamoto, J. Biphasic structure model for reversed micelles. Depressed acid dissociation of excited-state pyranine in the restricted reaction field. J. Phys. Chem. 1982, 86, 4826-4831. 

We shall describe the various steps in the evolution of the methods and knowledge of proton diffusion on the membrane surface. The methods used for our studies all emanate from one basic technique—the laser-induced proton pulse (I). The common step of the various forms of this method is a pulse excitation of aromatic alcohols (OH), such as naphthols, sulfono naphthols, or pyranine (8-hydroxypyrene- 1,3,6-trisulfonate), to their first excited electronic singlet state (OH ). In this state the compound is very acidic and the hydroxyl proton dissociates in subnanosecond dynamics. 

Our work [9-13] has centered on the dye molecule shown in Figure 1. This molecule is officially called 8-hydroxypyrene 1,3,6-trisulfonate and colloquially known as pyranine or HPTS. We also denote it by ROH. Dissolved as its trisodium salt, it is already triply charged in its ground state, where the pK value of the OH group is around 8. In the first excited singlet state the hydroxy group becomes highly acidic [5], with a pK value of 1.4. 

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