Excited-State Proton Transfer from 4-Hydroxy-1-naphthalenesulfonate to Urea

Abstract

The excited-state proton transfer from 4-hydroxy-1-naphthalenesulfonate to urea has been studied in methanol at 25 °C. The decay of the acidic form is single-exponential for all urea concentrations. The proton acceptor concentration has been found to increase nonlinearly with the concentration of urea. The nonlinear behavior is explained by a model proposing urea monomers and, in particular, urea dimers to be the proton acceptors in methanol.

Triplet-State Characteristics and Photoionization Behavior of 2,2‘- and 4,4‘-Biphenyldiol Studied by 248 nm Laser Flash Photolysis in Aqueous Solutions

“…It is thus expected that the crossing of the PE surfaces in the present cases should be symmetry forbidden. However, as the PI of the phenolate ions following UV excitation is quite common, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]34 there seems to be a reasonable mixing between the π and σ states at the crossing point, probably due to an appreciable change in the molecular geometry, which causes a switch from the 1 π 1 state to the 3 σ 0 state to be possible.…”

“…Phenols and their derivatives are important probe molecules for investigating some of the fundamental processes occurring in many chemical and biological systems, namely, protontransfer and hydrogen-bonding interactions. [1][2][3][4][5] Behavior of phenols in their excited states is also of great significance because they closely resemble the chromophoric structures of the aromatic amino acids. It is well-known that the photoionization (PI) of aromatic amino acids plays a crucial role in the photodegradation of proteins.…”

“…Phenols and their derivatives are important probe molecules for investigating some of the fundamental processes occurring in many chemical and biological systems, namely, proton-transfer and hydrogen-bonding interactions. − Behavior of phenols in their excited states is also of great significance because they closely resemble the chromophoric structures of the aromatic amino acids. It is well-known that the photoionization (PI) of aromatic amino acids plays a crucial role in the photodegradation of proteins. − Though considerable efforts have been made to understand the excited-state behavior of phenols, indoles, and aromatic amino acids, the mechanistic details of the PI processes in these molecules are not yet very clear. − In many phenolic molecules, it has been observed that the fluorescence quantum yield (Φ f ) is largely dependent on the excitation energy. − Thus, Φ f is seen to drop drastically when the molecules are excited to electronic states (S n ) higher than the S 1 state. − It has been observed that in many phenolic molecules the PI follows both mono- and biphotonic pathways, depending on the experimental conditions. − Though the involvement of the triplet states has been proposed for the biphotonic ionization of these molecules, , the mechanism is not very clear in many cases.…”

“…Recently, we have investigated the triplet-state characteristics of the two diols in different organic solvents using a nanosecond laser flash photolysis (LFP) technique and observed substantial differences in their behavior. Because the photochemical behavior of phenols and related molecules in aqueous solutions is more important, − in the present work, we have investigated the triplet-state and PI/photodissociation (PD) characteristics of the two diols in aqueous solutions under different pH conditions. The aim of this work is to understand in detail how the presence and absence of the intramolecular hydrogen bonding in the two biphenyldiols affect their photochemical behavior in aqueous solutions under 248 nm laser excitation.…”

Excited singlet (S1) state interactions of 2,2′- and 4,4′-biphenyldiols with chloroalkanes: Photoinduced dissociative electron transfer

“…[1][2][3][4][5][6][7][8] Studies on the photoinduced ET ͑PET͒ processes, especially on the dynamical aspects of these reactions, received the momentum for the last 2 decades, mostly due to the advent of the fast and ultrafast spectroscopic techniques covering the nano, pico to femtosecond time domain. [9][10][11][12][13][14][15] The main aim of such studies is to obtain the detailed insight into the kinetics, dynamics and mechanism of the ET processes through real time observations.…”