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Impact of Fluorination on the Photophysics of the Flavin Chromophore: A Quantum Chemical Perspective

Abstract

10-methylisoalloxazine (MIA) as well as its mono-fluorinated derivatives (6-9F-MIA) were investigated by means of quantum chemistry, looking into the influence of fluorination on fluorescence, absorption as well as inter-system crossing (ISC). A maximized fluorescence quantum yield (ΦFl ) of this chromophore is desirable for application as a potential fluorescence marker in biodiagnostics / photobiological studies. Enhanced triplet quantum yield ΦT on the other hand may open a perspective for photodynamic therapies (PDT) in cancer treatment. Determination of equilibrium geometries was carried out employing (time-dependent) Kohn-Sham density functional theory and electronic properties were obtained using a combined density functional theory and multi-reference configuration interaction (DFT/MRCI) method. In gas phase, an El-Sayed-favored 1 (ππ*) ->3 (nπ*)-ISC enables population transfer to the triplet domain on a timescale of 10^9 s−1, i.e. significantly faster than fluorescence (kFl ≈ 10^7 s−1 ). Two different models were applied to investigate the influence of aqueous medium on absorption and relaxation: The implicit solvation model A is the well-established conductor-like screening model (COSMO) and hybrid model B combines quantum mechanical micro-hydration and conductor-like screening. Polar, protic environment leads to a significant blueshift of the nπ potentials, slowing down the ISC process to 10^7 − 10^8 s−1 now enabled by vibronic spin–orbit coupling. Fluorination effects are additive, this principle can be utilized to predict the photophysical properties of multiply fluorinated derivatives.

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Publication details

The article was received on 08 Feb 2019, accepted on 15 Apr 2019 and first published on 16 Apr 2019


Article type: Paper
DOI: 10.1039/C9CP00805E
Citation: Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Impact of Fluorination on the Photophysics of the Flavin Chromophore: A Quantum Chemical Perspective

    M. Bracker, F. Dinkelbach, O. Weingart and M. Kleinschmidt, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP00805E

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