An approach to the development of fluorescent probes to follow polymerizations in situ using fluorinated cross-conjugated enediynes (Y-enynes) is reported. Different substitution patterns in the Y-enynes result in distinct solvatochromic behavior. β,β-Bis(phenylethynyl)pentafluorostyrene 7, which bears no donor substituents and only fluorine at the styrene moiety, shows no solvatochromism. Donor substituted β,β-bis(3,4,5-trimethoxyphenylethynyl)
pentafluorostyrene 8 and β,β-bis(4-butyl-2,3,5,6-tetrafluorophenylethynyl)-3,4,5-trimethoxystyrene 9
exhibit solvatochromism upon change of solvent polarity. Y-enyne 8 showed the largest solvatochromic shift (94 nm bathochromic shift) upon changing solvent from cyclohexane to acetonitrile. A smaller solvatochromic response
(44 nm bathochromic shift) was observed for 9. Lippert–Mataga treatment of 8 and 9 yields slopes of -10,800 and -6,400 cm -1, respectively. This corresponds to a change in dipole moment of 9.6 and 6.9 D, respectively. The solvatochromic behavior in 8 and 9 supports the formation of an intramolecular charge transfer (ICT) state. The low fluorescence quantum yields are caused by competitive double bond rotation. The fluorescence decay time of 9 decreases in methyltetrahydrofuran from 2.1 ns at 77 K to 0.11 ns at 200 K. Efficient single bond rotation in 9 was frozen at -50 °C in a configuration in which the trimethoxyphenyl ring is perpendicular to the fluorinated rings.
7–9 are photostable compounds. The X-ray structure of 7 shows it is not planar and that its conjugation is distorted.
Y-enyne 7 stacks in the solid state showing coulombic, actetylene–arene, and fluorine–π interactions.
| Identifer | oai:union.ndltd.org:Potsdam/oai:kobv.de-opus-ubp:1316 |
| Date | January 2002 |
| Creators | Kaafarani, Bilal R., Wex, Brigitte, Strehmel, Bernd, Neckers, Douglas C. |
| Publisher | Universität Potsdam, Mathematisch-Naturwissenschaftliche Fakultät. Institut für Chemie, Extern. Extern |
| Source Sets | Potsdam University |
| Language | English |
| Detected Language | English |
| Type | Postprint |
| Format | application/pdf |
| Source | Photochemical and Photobiological Sciences. - ISSN 1474-905X. - 1 (2002), p. 942-950 |
| Rights | http://opus.kobv.de/ubp/doku/urheberrecht.php |
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