Proton-Transfer Fluorescence

Keywords Excited-state intramolecular proton transfer Fluorescence dye Photoinduced electron transfer Proton coupled electron transfer Relaxation dynamics... 

Sytnik A, Del Valle JC (1995) Steady-state and time-resolved study of the proton-transfer fluorescence of 4-hydroxy-5-azaphenanthrene in model solvents and in complexes with human serum albumin. J Phys Chem 99 13028-13032... 

Fig. 46. Scheme of optical transitions, explaining the dual fluorescence resulting from proton transfer in excited electronic state. 

Hydrogen transfer in excited electronic states is being intensively studied with time-resolved spectroscopy. A typical scheme of electronic terms is shown in fig. 46. A vertical optical transition, induced by a picosecond laser pulse, populates the initial well of the excited Si state. The reverse optical transition, observed as the fluorescence band Fj, is accompanied by proton transfer to the second well with lower energy. This transfer is registered as the appearance of another fluorescence band, F2, with a large anti-Stokes shift. The rate constant is inferred from the time dependence of the relative intensities of these bands in dual fluorescence. The experimental data obtained by this method have been reviewed by Barbara et al. [1989]. We only quote the example of hydrogen transfer in the excited state of... 

Up to the present the principal interest in heteroaromatic tautomeric systems has been the determination of the position of equilibrium, although methods for studying fast proton-transfer reactions (e.g., fluorescence spectroscopy and proton resonance ) are now becoming available, and more interest is being shown in reactions of this type (see, e.g., references 21 and 22 and the references therein). Thus, the reactions of the imidazolium cation and imidazole with hydroxyl and hydrogen ions, respectively, have recently been demonstrated to be diffusion controlled. ... 

Discussion of topics corresponding to proton transfer occurring in the excited state are included under Fluorescence Spectroscopy and Excited... 

VIIL Fluorescence Spectroscopy and Excited State Proton Transfer... 

Poly(aryl ether) branches of generation 1 to 3 have been appended to a pho-totautomerizable quinoHne core to investigate the effect of dendritic architecture on the excited state intramolecular proton transfer [45]. The changes observed in the absorption and emission spectra on increasing dendrimer generation indicate that the dendritic branches affect the planarity of the core and therefore the efficiency of the excited state intramolecular proton transfer and of the related fluorescence processes. 

Itoh, M. Adachi, T. Transient absorption and two-step laser excitation fluorescence studies of the excited-state proton transfer and relaxation in the methanol solution of 7-hydroxyflavone. J. Am. Chem. Soc. 1984, 106, 4320 -324. 

Itoh, M. Hasegawa, K. Fujiwara, Y. Two-step laser excitation fluorescence study of the ground- and excited-state proton transfer in alcohol solutions of 7-hydroxyisoflavone. J. Am. Chem. Soc. 1986, 108, 5853-5857. 

It has been shown that photoexcitation of the guanine-cytosine (G-C) base pair leads to proton transfer [231], Watson-Crick (WC) base pairs have excited state lifetimes much shorter than other non-WC base pairs indicating once again that the natural occurring WC base pairs are more photostable than other alternative configurations [115, 118, 232-235], Much work has been done in the gas phase where many different base pair isomers exist. The ultrafast relaxation of the WC base pair has also been confirmed in solution using fluorescence up-conversion measurements [117]. 

This agrees quite well with the rate constants for intramolecular proton transfer in 2,4-bis(dimethyl-amino )-6-(2-hydroxy-5-methylphenyl)-5-triazine which had been measured by Shizuka et al. ( l6) using laser picosecond spectroscopy. The fluorescence decay constant t of (TIN) was found to be 60 20 ps. Because of the weak intensity all fluorescence lifetimes refer to the pure substance in crystalline form at room temperature. 

Using picosecond flash spectroscopy Gupta et al. 2k) reported for 2-hydroxyphenylbenzotriazole in ethanol a short-lived transient (6 ps) followed by a transient absorption whose lifetime is estimated to be 600 ps. The authors assigned the short-lived transient to the "vertical singlet" while the long-lived transient is presumably the "proton transferred species". These measurements of transient absorptions with the picosecond flash method confirm our results derived from the fluorescence emission using the phase fluorimetric method. 

Excited-state intramolecular proton transfer (ESIPT) exhibits different regularities [49, 50]. Commonly, this is a very fast and practically irreversible reaction proceeding along the H-bonds preexisting in the ground state. Therefore, only the reaction product band is seen in fluorescence spectra. Such cases are not interesting for designing the fluorescence reporters. The more attractive dual emission is... 

Hsieh C-C, Ho M-L, Chou P-T (2010) Organic dyes with excited-state transforma-tions (electron, charge and proton transfers). In Demchenko AP (ed) Advanced Fluorescence Reporters in Chemistry and Biology I. Springer Ser Fluoresc 8 225-266... 

Yushchenko DA, Shvadchak W, Bilokin MD, Klymchenko AS, Duportail G, Mely Y, Pivovarenko VG (2006) Modulation of dual fluorescence in a 3-hydroxyquinolone dye by perturbation of its intramolecular proton transfer with solvent polarity and basicity. Photochem Photobiol Sci 5 1038-1044... 

Klymchenko AS, Demchenko AP (2003) Multiparametric probing of intermolecular interactions with fluorescent dye exhibiting excited state intramolecular proton transfer. Phys Chem Chem Phys 5 461 -68... 

Bimolecular reactions with paramagnetic species, heavy atoms, some molecules, compounds, or quantum dots refer to the first group (1). The second group (2) includes electron transfer reactions, exciplex and excimer formations, and proton transfer. To the last group (3), we ascribe the reactions, in which quenching of fluorescence occurs due to radiative and nonradiative transfer of excitation energy from the fluorescent donor to another particle - energy acceptor. 

The second group of intermolecular reactions (2) includes [1, 2, 9, 10, 13, 14] electron transfer, exciplex and excimer formations, and proton transfer processes (Table 1). Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. PET is involved in many photochemical reactions and plays... 

Van Benthem MH, Gillispie GD (1984) Intramolecular hydrogen bonding. 4. Dual fluorescence and excited-state proton transfer in 1, 5-dlhydroxyanthraqulnone. J Phys Chem 88 2954-2960... 

Jang DJ, Kelley DF (1985) Time-resolved and steady-state fluorescence studies of the excited-state intramolecular proton transfer and relaxation of 2-hydroxy-4, 5-naphthotro-pone. J Phys Chem 89 209-211... 

Wang H, Zhang H, Abou-Zied OK et al (2003) Femtosecond fluorescence upconversion studies of excited-state proton-transfer dynamics in 2-(20-hydroxyphenyl)benzoxazole (HBO) in liquid solution and DNA. Chem Phys Lett 367 599-608... 

Sytnik A, Kasha M (1994) Excited-state intramolecular proton transfer as a fluorescence probe for protein binding-site static polarity. Proc Natl Acad Sci USA 91 8627-8630... 

---