title: Photophysics and photodeprotection reactions of p-methoxyphenacyl phototriggers: an ultrafast and nanosecond time-resolved spectroscopic and density functional theory study.
abstract: Time-resolved spectroscopic experiments were performed to investigate the kinetics and mechanisms of the photodeprotection reactions for p-methoxyphenacyl (pMP) compounds, p-methoxyphenacyl diethyl phosphate (MPEP) and diphenyl phosphate (MPPP). The experimental results reveal that compared to the previous reports for the counterpart p-hydroxyphenacyl (pHP) phosphates, the (3)npi*/pipi* mixed character triplet of pMP acts as a reactive precursor that leads to the subsequent solvent and leaving group dependent chemical reactions and further affects the formation of photoproducts. The MPPP triplet in H(2)O/CH(3)CN and in fluorinated alcohols shows a rapid heterolytic cleavage (tau approximately 5.4 ns) that results in deprotection and formation of a solvolytic rearrangement product, whereas the MPPP triplet in CH(3)CN and the MPEP triplet in CH(3)CN and H(2)O/CH(3)CN and fluorinated alcohols decay on a much longer time scale (tau approximately 100 ns) with little observation of the rearrangement product. The density functional theory (DFT) calculations reveal a substantial solvation effect that is connected with the methoxy versus hydroxyl substitution in accounting for the different deprotection reactivity of pMP and pHP compounds. The results reported here provide new insight in elucidating the solvent and leaving group dependent dual reactivity of pMP compounds on the formation of the rearrangement versus reductive photoproduct.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong S. A. R., P. R. China.
authors.forename: Hui-Ying
authors.initials: HY
authors.lastname: An
authors.forename: Wai Ming
authors.initials: WM
authors.lastname: Kwok
authors.forename: Chensheng
authors.initials: C
authors.lastname: Ma
authors.forename: Xiangguo
authors.initials: X
authors.lastname: Guan
authors.forename: Jovi Tze Wai
authors.initials: JT
authors.lastname: Kan
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Toy
authors.forename: David Lee
authors.initials: DL
authors.lastname: Phillips
mesh_terms: D000447:Aldehydes / Q000138:chemical synthesis* / Q000737:chemistry; D003198:Computer Simulation; D004952:Esters / Q000138:chemical synthesis* / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D010777:Photochemistry; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D013997:Time Factors
chemical_list: D000447:Aldehydes; D004952:Esters