title: Solvent organization around the perfluoro group of coumarin 153 governs its photophysical properties: An experimental and simulation study of coumarin dyes in ethanol as well as fluorinated ethanol solvents.
abstract: The self-aggregation property of the perfluoro group containing molecules makes it important in the research fields of biology and polymer and organic synthesis. In the quest of understanding the role of the perfluoro group on the photophysical properties of perfluoro-containing molecules in biologically important fluoroethanol solvents, we have applied photophysical as well as molecular dynamics simulation techniques to explore the properties of perfluoro groups containing molecule coumarin-153 (C153) in ethanol (ETH), monofluoroethanol (MFE), difluoroethanol (DFE), and trifluoroethanol (TFE) and compared them with the molecules without perfluoro moiety, namely coumarin-6H (C6H) and coumarin-480 (C480). In contrast to C6H and C480, the excited state lifetime of C153 in fluorinated ETHs is not monotonic. The excited state lifetime of C153 decreases in MFE and DFE as compared to ETH, whereas in TFE, it increases as compared to MFE and DFE. Molecular dynamics simulation reveals that the carbon terminal away from the OH group of fluorinated ETHs has a preferential orientation near the perfluoro (CF3) group of C153. In MFE and DFE, the CF3 group of C153 prefers to have a CF2-F⋯H -(CHF) type of electrostatic interaction over CF2-F⋯F -(CH2) kind of dispersion interaction which increases the rate of nonradiative decay, probably due to the electrostatic nature of the CF2-F⋯H -(CHF) hydrogen bond. On the other hand, in TFE, C-F⋯ F-C type of dispersion interaction, also known as fluorous interaction, takes place between the CF3 groups of C153 and TFE which decreases the rate of nonradiative rate as compared to MFE and DFE, leading to the increased lifetime of C153 in TFE. Photophysical and MD simulation studies clearly depict that the structural organization of solvents and their interaction with the fluorocarbon group are crucial factors for the photophysical behavior of the fluorocarbon containing molecules.
authors.affiliation: Department of Spectroscopy, Indian Association for the Cultivation of Science, Kolkata 700032, India.
authors.forename: Saptarsi
authors.initials: S
authors.lastname: Mondal
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India.
authors.forename: Ritaban
authors.initials: R
authors.lastname: Halder
authors.affiliation: Department of Spectroscopy, Indian Association for the Cultivation of Science, Kolkata 700032, India.
authors.forename: Biswajit
authors.initials: B
authors.lastname: Biswas
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India.
authors.forename: Biman
authors.initials: B
authors.lastname: Jana
authors.affiliation: Department of Spectroscopy, Indian Association for the Cultivation of Science, Kolkata 700032, India.
authors.forename: Prashant Chandra
authors.initials: PC
authors.lastname: Singh
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D000431:Ethanol / Q000031:analogs & derivatives* / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry*; D006860:Hydrogen Bonding; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D011807:Quinolizines / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D003374:Coumarins; D005456:Fluorescent Dyes; D005466:Fluorocarbons; D011807:Quinolizines; D012997:Solvents; C488877:coumarin 153; C000614673:coumarin-6H; C573700:coumarin 480; D000431:Ethanol