Huang Guanheng, Zhou Chen, Liang Runhui, Sun Shanshan, Deng Ziqi, Li Jiayu, Dang Li, Phillips David Lee, Li Ming-De
Department of Chemistry and Key Laboratory for Preparation and Application of Ordered Structure Materials of Guangdong Providence, Shantou University, Shantou515063, China.
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China.
J Phys Chem B. 2022 Nov 17;126(45):9388-9398. doi: 10.1021/acs.jpcb.2c06452. Epub 2022 Nov 4.
The photophysical and photochemical reaction pathways of -methylbenzophenone (-MeBP) in different solutions were investigated by employing femtosecond to nanosecond transient absorption and nanosecond time-resolved resonance Raman spectroscopy methods. In pure acetonitrile, neutral or pH 1 aqueous solutions, -MeBP exhibit similar excited-state evolutions upon excitation in which -MeBP will experience excitation to an excited state then undergo intersystem crossing and solvent arrangement followed by 1,5 hydrogen atom transfer processes to form the first singlet excited state, triplet state (n, π*), biradical intermediates, and enol form transients, respectively. However, in a pH 0 acidic solution, the protonation of -MeBP will form the cation biradical intermediate that facilitates radical coupling to generate a benzocyclobutanol product, which causes a dramatic reduction of the lifetime of the enol form transients. In contrast, in sodium bicarbonate solution, the biradical intermediate may be quenched by the bicarbonate ion to construct a C-C bond and form the carboxylic acid that causes a fast decay of biradical intermediate. These results demonstrate that the photophysical and photochemical reaction pathways of -MeBP are pH-dependent in aqueous solution which may be very useful for the capture of CO capture by photoexcitation of aromatic ketones.
