Substituent and Solvent Effects on the Nature of the Transitions of Pyrenol and Pyranine. Identification of an Intermediate in the Excited-State Proton-Transfer Reaction † (original) (raw)
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Coherent intermolecular proton transfer in acid-base reaction of excited state pyranine
Royal Society of Chemistry
Detailed molecular dynamics of an acid-base reaction has been the subject of extensive investigations. Here we report excited state proton transfer dynamics of pyranine (8-hydroxypyrene-1{,}3{,}6-trisulfonic acid{,} HPTS) in acetate buffer by time-resolved fluorescence (TF) and quantum mechanical/effective fragment potential molecular dynamics (QM/EFP-MD) simulation. High time resolution in TF and TF spectra measurements allow acquisition of accurate reaction kinetics. Upon photoexcitation of HPTS{,} the proton (deuterium) is transferred coherently to acetate in 60 fs (80 fs) for a contact pair of HPTS (DPTS) and acetate by hydrogen bond{,} which comprises approximately 28 % of the population. ESPT proceeds slowly in picosecond time scale for the remaining HPTS as reported previously. Coherent wave packet motions of the reactant (acid) and the product (conjugate base) enable acquisition of the vibrational spectra of excited states via TF (VETF). Comparison of the VETFs of the reactant and product and calculation of the Huang-Rhys factors (vibrational reorganization energies) identify the vibrational modes that actively participate the coherent proton transfer. In particular{,} the 246 cm-1 vibrational mode{,} which consists of in-plane skeletal stretching motion{,} promotes the ESPT by transferring the donor oxygen towards the acceptor oxygen in acetate. QM/EFP MD simulation corroborates the experiment and provides molecular details of the ESPT.
Journal of Physical Chemistry A, 2006
Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k 1 ) is calculated to be ~1 × 10 9 M -1 s -1 . This is slower by about two orders of magnitude than that in bulk water (8 × 10 10 M -1 s -1 ) at 4 M acetate.
Proton Transfer Reaction Dynamics of Pyranine in DMSO/Water Mixtures
Chemphyschem : a European journal of chemical physics and physical chemistry, 2018
Photoinduced intermolecular excited-state proton transfer (ESPT) reactions are ubiquitous in chemistry and biology. ESPT reactions are extremely sensitive to the nature of water molecules in its microenvironment and thus serve as a sensitive reporter for the water structure and dynamics in a system. Herein, the photoinduced intermolecular ESPT reaction of 8-hydroxypyrene-1,3,5-trisulfonic acid (HPTS, also known as pyranine) has been investigated in various DMSO/water mixtures by using steady-state and time-resolved emission spectroscopy. The DMSO/water binary mixture yields an interesting and anomalous behavior for the proton transfer reaction dynamics of HPTS at a mole fraction of DMSO (X) of 0.41-0.51, which has also been previously investigated and projected as an anomalous region by molecular dynamics simulation and other experimental techniques. The extreme slowdown of the proton transfer reaction observed at X=0.41-0.51 has been attributed to the slow solvation dynamics, as we...
Photo-induced excited-state proton transfer (ESPT) reactions are of central importance in many biological and chemical processes. Based on the results of a joint study using optical pump THz probe (OPTP) spectroscopy and molecular dynamics simulations, we were able to elucidate the ultrafast changes in the solvation environment for three derivatives of pyranine: the photoacid HPTS, the methoxy derivative MPTS, and the photobase OPTS. Experimentally, we find damped oscillations in the THz signal at short times and our simulations enable their assignment to vibrational energy transfer beatings between the photoexcited chromophore and nearby solvent molecules. The simulations of HPTS reveal strikingly efficient sub-ps energy transfer into a particular solvent mode, that is active near 4 THz, and which can provide the requisite energy required for solvent reorganization promoting proton transfer. Similar oscillations are present in the THz signal for all three derivatives, however the s...
Excited state proton transfer from pyranine to acetate in a CTAB micelle
Chemical Physics Letters, 2004
Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k 1 ) is calculated to be ~1 × 10 9 M -1 s -1 . This is slower by about two orders of magnitude than that in bulk water (8 × 10 10 M -1 s -1 ) at 4 M acetate.
Computational and Theoretical Chemistry, 2013
Density functional theory (B3LYP and CAM-B3LYP) and MP2 methods have been employed to study of proton transfer in annular tautomerism and double proton transfer reaction of a series of pyrazoles substituted at the 4 position (NH 2 , OH, CH 3 , F, H, Cl, CN, NO 2 , CHO, NO). It was found that activation energy for monomers of pyrazole derivatives via tautomerism process is in the range of 47.8-55.5 kcal/mol. In addition the pyrazole with electron releasing groups have lower activation energy than electron withdrawing ones. Moreover it was found that formation of dimers favored, and corrected interaction energies were found in the range of 11.
Journal of Luminescence, 2014
Excited state proton transfer processes in vitreous glasses and in solid mixtures are investigated by steady state fluorimetry and laser flash photolysis kinetic studies with the photoacids pyranine and 2-naphthol. Glasses were derived from TEOS by the sol-gel condensation process and hydrated solid mixtures from NaCl or KH 2 PO 4 /K 2 HPO 4 crystals. The extent of the water content necessary for the reaction is determined. Shrinkage of TEOS derived monoliths from water loss leads to an increase in proton transfer extent due to the increase in local concentrations of accepting and donor buffer species, but the concomitant increase in the ionic strength actuates in an opposite direction. Furthermore, water losses by aging of air-exposed gel goes to a critical 20% weight fraction, beyond it proton transfer reactions are hindered. Similar studies with solid NaCl or solid phosphate buffer mixtures demonstrated the same critical water level indicating that free water molecules are crucial for the proton to escape from the original cage where the geminate ion pair [-||RO À n H þ ||-] is formed and can undergo coupled proton transfer reactions.
Study of Proton Transfer Reaction Dynamics in Pyrrole 2-Carboxyldehyde
2009
Photophysical and photochemical dynamics of ground state and excited state proton transfer reaction is reported for Pyrrole 2-Carboxyldehyde (PCL). Steady state absorption and emission measurements are conducted in PCL. The theoretical investigation is done by using different quantum mechanical methods (e.g. Hartree Fock, DFT, MP2, CCSD etc.). The reaction pathway and two dimensional potential energy surfaces are computed in various level of theory. A transition state is also reported in gas phase and reaction filed calculation. It is established that PCL forms different emitting species in different media. A large Stokes shifted emission band, which is attributed to species undergoing excited state intramolecular proton transfer, is observed in hydrocarbon solvent. Intermolecular proton transfer is observed in hydroxylic polar solvent. Experimental observations yield all possible signatures of intramolecular and intermolecular proton transfer in excited state of PCL. The origins of these signatures have been explained successfully using corresponding quantum mechanical theories.