Abstract
We employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan-1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (≈160 fs) to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (≈10 ps) followed by decay (≈390 ps) to the corresponding ground state.
Highlights
Excited-state intramolecular proton transfer (ESIPT) is one of the most successful model systems for the examination of complex proton transfer dynamics.1–3 In a photoinduced ESIPT reaction, a proton moves from the donor to an acceptor group within the same molecule upon a change in electronic charge distribution in response to an electronic excitation
which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond
an ultrafast process occurring on a subpicosecond time scale
Summary
Excited-state intramolecular proton transfer (ESIPT) is one of the most successful model systems for the examination of complex proton transfer dynamics. In a photoinduced ESIPT reaction, a proton moves from the donor to an acceptor group within the same molecule upon a change in electronic charge distribution in response to an electronic excitation. Excited-state intramolecular proton transfer (ESIPT) is one of the most successful model systems for the examination of complex proton transfer dynamics.. The origin of strongly red-shifted fluorescence spectra in these and related compounds is believed to originate from a profound rearrangement of the molecular structure, resulting from proton transfer along a pre-existing intramolecular H-bond after electronic excitation. The real-time dynamics of such a proton transfer in various ESIPT molecular systems have been explored in the gas phase, techniques applied to ESIPT in solution comprise time-resolved fluorescence based on streak cameras, time-correlated single-photon counting, and upconversion, as well as transient absorption (TA) with pump/probe combinations being UV/mid-IR, UV/VIS, and recently UV/UV..
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