Picosecond studies of excited-state protonation and deprotonation kinetics. The laser pH jump
By measuring the time history of both anionic and acidic species under a variety of experimental conditions and using a kinetic scheme which includes terms for the fluorescence lifetimes and quenching the complete kinetics of excited state protonation and deprotonation have been obtained for 2-naphthol-6-sulfonate, k/sub f/ = (1.02 +- .2) x 10/sup 9/ s/sup -1/ and k/sub b/ = (9.0 +- 3) x 10/sup 10/L mol/sup -1/s/sup -1/. From the reaction, it is seen that one hydronium ion is produced for each proton transfer. Since the excited-state lifetime of 2-naphtholate-6-sulfonate is approx.10 ns, while the proton transfer time is <1 ns, excited-state acid-base equilibrium is achieved. Knowing the 2-naphthol-6-sulfonate absorption coefficient is 255 nm, its excited-state pK/sub a/ value, the UV pulse energy, and the excitation geometry, it is calculated that the H/sub 3/O/sup +/ concentration was increased by 10/sup -4/M. The solution had a pH of 7 before excitation, and was rapidly modulated to pH less than or equal to 4 on a time scale given by the subns proton-transfer rate. The pH will return to its previous value on a time scale greater than or equal to the excited state lifetime (tau approx. 10 ns), since it is the protonation rate of ground state anions which determines how rapidly the ground-state acid-base equilibrium is reestablished. 2 figures.
- Research Organization:
- Los Alamos Scientific Lab., New Mexico
- OSTI ID:
- 6428915
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 101:3; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500 -- Photochemistry
AROMATICS
BARYONS
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DATA FORMS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY LEVELS
EQUILIBRIUM
ESTERS
EXCITED STATES
EXPERIMENTAL DATA
FERMIONS
GRAPHS
HADRONS
HEAT TREATMENTS
HYDROXY COMPOUNDS
INFORMATION
IONS
KINETICS
LASER RADIATION
MODULATION
MOLECULAR IONS
NAPHTHOLS
NUCLEONS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXONIUM IONS
PH VALUE
PHENOLS
PHOTOCHEMICAL REACTIONS
PHOTOGRAPHY
PHOTOLYSIS
PROTONS
QUENCHING
RADIATIONS
REACTION KINETICS
STREAK PHOTOGRAPHY
SULFONIC ACID ESTERS
TIME DEPENDENCE