Water-Assisted Self-Photoredox of 3-(Hydroxymethyl)benzophenone: An Unusual Photochemistry Reaction in Aqueous Solution

Solvent assisted photochemical formation of a new keto[3,3]paracyclophane

Photolysis of a phenacyl benzoate tethered with a phenol leads to a very efficient release of benzoic acid, which is suggested to occur by electron transfer and/or proton transfer from the remote phenol moiety to the triplet excited carbonyl. Photolysis of the compound in protic solvents forms a new keto[3,3]paracyclophane.

Mechanism and kinetics of photochemical transformation of ketoprofen and its degradation intermediates

Ketoprofen, 2-(3-benzoylphenyl)-propionic acid, a widely used non-steroidal anti-inflammatory drug, is considered as an important water pollutant. Kinetics and mechanism of its photolytic transformation in aqueous solutions was studied experimentally and partial reaction steps were modelled by means of quantum chemistry methods. While the rate of ketoprofen photolysis was not significantly affected by its acid-base equilibrium, a marked influence of pH on the subsequent degradation reactions was observed. At pH 1.3, two oxygenated primary products were identified, that underwent fast photolysis. Deprotonated form of ketoprofen was transformed preferentially to ethylbenzophenone and further degradation proceeded substantially slower. Oxygen participated on photolytic processes both as a reactant and the triplet state quencher. The active involvement of water molecules in the reaction mechanism was investigated by comparative experiments in acetonitrile. The phototransformation mechanism proposed based on the experimental data corresponded well with the theoretical results.

A quantum-chemical insight into the tunable fluorescence color and distinct photoisomerization mechanisms between a novel ESIPT fluorophore and its protonated form

Enol-keto proton tautomerization and cis-trans isomerization reactions of a novel excited-state intramolecular proton transfer (ESIPT) fluorophore of BTImP and its protonated form (BTImP⁺) were explored using density functional theory/time-dependent density functional theory (DFT/TD-DFT) computational methods with a B3LYP hybrid functional and the 6-31+G(d,p) basis set. In addition, the absorption and fluorescence spectra were calculated at the TD-B3LYP/6-31+G(d,p) level of theory. Our results reveal that both BTImP and BTImP⁺ can undergo an ultrafast ESIPT reaction, giving rise to the single fluorescence emission with different fluorescence colors, which are nicely consistent with the experimental findings. Calculations also show that following the ultrafast ESIPT, BTImP and BTImP⁺ can experience the distinctly different cis-trans isomerization processes. The intersystem crossing between the first excited singlet S₁ state and triplet T₁ state is found to play an important role in the photoisomerization process of BTImP⁺. In addition, the energy barrier of the trans-keto→cis-keto isomerization in the ground state of BTImP⁺ is calculated to be 10.49kcalmol^-1, which implies that there may exist a long-lived trans-keto species in the ground state for BTImP⁺.

To Photoredox or Not in Neutral Aqueous Solutions for Selected Benzophenone and Anthraquinone Derivatives

The experimental and theoretical results in neutral aqueous solutions reported here indicate that a proton-coupled electron transfer (PCET) from an alcohol C-H bond to the para-carbonyl is the initial and crucial process for the photoredox reaction of 2-(1-hydroxyethyl)-anthraquinone (HEAQ) to occur while the counterpart 3-(hydroxymethyl)-benzophenone (3-BPOH) compound displays a different PCET from an alcohol O-H bond to the carbonyl as the first step, followed by an intersystem crossing process that does not lead to the analogous photoredox, which is caused by a subtle charge-radical coupled effect between HEAQ and 3-BPOH. This can account for experimental results in the literature that HEAQ can undergo efficient photoredox but 3-BPOH does not under neutral aqueous conditions. These results have implications for the pH-dependent photochemical behavior of aromatic carbonyl compounds in aqueous media.

Water-assisted self-photoredox of 2-(1-hydroxyethyl)-9,10-anthraquinone through a triplet excited state intra-molecular proton transfer pathway

A novel self-photoredox reaction for 2-(1-hydroxyethyl)-9,10-anthraquinone has been theoretically rationalized to take place through two steps of triplet excited state intra-molecular proton transfer aided by water wires.