title: Solvation oscillations and excited-state dynamics of 2-amino- and 2-hydroxy-7-nitrofluorene and its 2'-deoxyriboside.
abstract: Push-pull substituted fluorenes are considered for use as dynamic solvation probes in polynucleotides. Their fluorescence band is predicted (by simulations) to show weak spectral oscillations on the subpicosecond time scale depending on the nucleotide sequence. The oscillations reflect the local far-infrared spectrum of the environment around the probe molecule. A connection is provided by the continuum theory of polar solvation which, however, neglects molecular aspects. We examine the latter using acetonitrile solution as a test case. A collective librational solvent mode at 100 cm(-1) is observed with 2-amino-7-nitrofluorene, 2-dimethylamino-7-nitrofluorene, 2-hydroxy-7-nitrofluorene, and its 2'-deoxyriboside. Different strengths of the oscillation indicate that rotational friction of nearby acetonitrile molecules depends on the solute structure or that H bonding is involved in launching the librational coherence. Polar solvation in methanol is used for comparison. With hydroxynitrofluorenes, the observation window is limited by intersystem crossing for which rates are reported. A prominent excited-state absorption band of nitrofluorenes at 430 nm can be used to monitor polar solvation. Structural and electronic relaxation pathways are discussed with the help of quantum chemical calculations.
authors.affiliation: Department of Chemistry, Humboldt University of Berlin, Berlin, Germany.
authors.forename: Venugopal
authors.initials: V
authors.lastname: Karunakaran
authors.forename: Matthias
authors.initials: M
authors.lastname: Pfaffe
authors.forename: Ilya
authors.initials: I
authors.lastname: Ioffe
authors.forename: Tamara
authors.initials: T
authors.lastname: Senyushkina
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Kovalenko
authors.forename: Rainer
authors.initials: R
authors.lastname: Mahrwald
authors.forename: Vadim
authors.initials: V
authors.lastname: Fartzdinov
authors.forename: Heinz
authors.initials: H
authors.lastname: Sklenar
authors.forename: Nikolaus P
authors.initials: NP
authors.lastname: Ernsting
mesh_terms: D000042:Absorption; D000097:Acetonitriles / Q000737:chemistry; D001483:Base Sequence; D005449:Fluorenes / Q000737:chemistry*; D005453:Fluorescence; D006860:Hydrogen Bonding; D000432:Methanol / Q000737:chemistry; D009010:Monte Carlo Method; D009841:Oligonucleotides / Q000737:chemistry / Q000235:genetics; D012266:Ribose / Q000031:analogs & derivatives* / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: C529972:2-amino-7-nitrofluorene; C529974:2-deoxyriboside-7-nitrofluorene; C529973:2-hydroxy-7-nitrofluorene; D000097:Acetonitriles; D005449:Fluorenes; D009841:Oligonucleotides; D012997:Solvents; D012266:Ribose; D000432:Methanol; C032159:acetonitrile