engleski

Ultrafast Transient Absorption of Phenolic and Adamantyl Compounds

Four phenolic and adamantyl compounds were studied by the means of ultrafast transient absorption. All of the compounds undergo a photochemical reaction of quinone methide generation after the excitation in the UV. Samples are: adamantyl-phenol, BODIPY-phenol, naphthol, adamantyl-naphthol. Adamantyl-phenol sample was studied in details while other samples were discussed qualitatively as theoretical simulations and analysis are still in progress. Quinone methides (QMs) are important intermediates in the chemistry and photochemistry of phenols [1]. Particularly important is the reactivity of QMs with biologically relevant nucleophiles including amino acids, proteins, nucleobases and DNA, and G-quadruplex structures [2]. There are still open questions regarding the photodehydration reaction leading to formation of QMs that we aim to resolve using tools of ultrafast spectroscopy. Measurements were done using a Coherent Libra Ti:Sapphire amplifier with frequency doubled NOPA output as the tunable UV pump beam (276nm) and the white light probe beam generated in CaF2. Pump pulse duration was ~20fs which ensured great time resolution but also the appearance of the problems considering coherent artefacts at around time zero due to high intensity of the pump pulses which interfered with global and kinetic analysis. Quantum chemical theoretical simulations using TD-DFT methods were carried out for adamantyl- phenol sample and gave photochemical reaction pathway as the result which suggested the formation of quinone methides in their ground state straight from the excited state adamantyl- phenol without any intermediates. Experimental measurements and analysis verified those results. Qualitative description of the results for the other 3 samples is given and the comparison of naphthol vs adamantly- naphthol is shown.

Ultrafast transient absorption ; quinone methides ; conical intersection

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