Signaling Recognition Events with Fluorescent Sensors and Switches.

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

The origin of ions in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is currently a matter of active research A number of chemical and physical pathways have been suggested for MALDI ion formation, including gas-phase photoionization, ion–molecule reactions, disproportionation, excited-state proton transfer, energy pooling, thermal ionization, and desorption of preformed ions These pathways and others are critically reviewed, and their varying roles in the wide variety of MALDI experiments are discussed An understanding of ionization pathways should help to maximize ion yields, control analyte charge states and fragmentation, and gain access to new classes of analytes © 1999 John Wiley & Sons, Inc Mass Spec Rev 17: 337–366, 1998

Ion formation in MALDI mass spectrometry

We have used knowledge of the electronic structure of excited states of acids to design molecules that exhibit enhanced excited-state acidity. Such “super” photoacids are the strongest reversible photoacids known and allow the time evolution of proton transfer to be examined in a wide array of organic solvents. This includes breaking/formation of the hydrogen bonds in hundreds of femtoseconds, solvent reorientation and relaxation in picoseconds, proton dissociation, and, finally, diffusion and geminate recombination of the dissociated proton, observed in nanoseconds.

Excited-state proton transfer: from constrained systems to "super" photoacids to superfast proton transfer.

Publisher Summary This chapter discusses acid–base properties of electronically excited states of organic molecules. Excited state pK-values are most easily accessible through the use of the Forster cycle. To perform this calculation for a particular molecule, it is necessary to know the ground state equilibrium constant for the reaction in question and to have some measure of the energy difference between the lowest vibrational level of the ground and the excited state in both the B and BH + forms. The effects of solvation on 0–0 energies are discussed. The changes in molecular fluorescence with acidity give information about the protolytic behavior of the excited singlet state of a compound. Two techniques, phase and pulse fluorometry, are used for the direct measurement of fluorescence decay rates. The excited state acid-base behavior of molecules has direct implications in the field of analytical fluorimetry and phosphorimetry.

Acid-Base Properties of Electronically Excited States of Organic Molecules

Benzophenone, like xanthone, shows the excited state pK order pK(T1) > pK(S1) > pK(S0), which is readily understood in terms of the S1–T1 splitting to be expected from the n–π* and π–π* states of the unprotonated and protonated forms respectively. Both fluorescence and phosphorescence occur from the protonated form at 77 K, but in fluid solutions the pK* values were not accessible to direct determination but were estimated by the Foster cycle. Transients were observed from both B and BH+ forms by flash spectroscopy. Several substituted benzophenones behaved similarly, but the p-phenyl compound has a different pK order (due to the larger π–π*S1–T1 splitting in the B form) and with the N-protonation of the p-amino compound the order is completely reversed. The pK* values for the phenolic ionization of the p-hydroxy compound are also reassessed.

Similar excited state pK behaviour of xanthone and the benzophenones

Xanthone, which has a ground state pK of –4.1, is shown to have a pK(S1) value of +0.96 by fluorescence intensity measurements and a pK(T1) of +3.0 by triplet-triplet absorption measurements. The unusual order pK(T1) >pK(S1) >pK(S0) is also reproduced in the Forster cycle values calculated from the absorption, fluorescence, and phosphorescence maxima, though the numbers thus obtained for pK(T1) and pK(S1) are 2 to 3 units more positive. Forster's Cycle applied to the triplet-triplet absorption spectra of the protonated and unprotonated species indicates that pK(T2) is –0.7, so that in basic strength the second triplet state lies between S0 and S1.

P. A. H. Wyatt

Papers

Acid-Base Properties of Electronically Excited States of Organic Molecules

Similar excited state pK behaviour of xanthone and the benzophenones

Excited singlet and triplet pK values of xanthone in aqueous solution

Aehnliches pk-verhalten im angeregten zustand von xanthon und 4,4′-substituierten benzophenonen

Pk-werte von xanthon im angeregten singulett- und triplettzustand in waessriger loesung