Authors: Bernd Strehmel¹; Kevin B. Henbest²; Ananda M. Sarker²; John H. Malpert²; D.Y. Chen²; Michael A.J. Rodgers²; Douglas C. Neckersa²

Source: Journal of Nanoscience and Nanotechnology, Volume 1, Number 1, March 2001 , pp. 107-124(18)

Publisher: American Scientific Publishers

Abstract:

The photochemical and photophysical properties of the crown ethers trans,trans-1,4-bis[2-(3,4-benzo 15-crown 5)ethenyl]-2,3,5,6-tetrafluorobenzene (1) and trans,trans-1,4-bis[2-(3,4-benzo 18-crown 6)ethenyl]-2,3,5,6-tetrafluorobenzene (2) were investigated in the absence and presence of groups I and II metal ions. The photophysical methods used include steady state fluorescence, uv spectroscopy, and ultrafast transient absorption spectroscopy. Both compounds showed solvatochromic behavior, due to intramolecular charge transfer state formation, and efficient fluorescence in polar solvents. Photophysical behavior was dependent on the metal ion. The addition of metal ions that completely fit into the crown ether cavity resulted in significant blue shifts in the fluorescence emission spectra (chemosensing properties). Partially fitting ions changed the fluorescence spectra slightly. Transient absorption measurements revealed fast and slow decay components with time constants of 10–20 and 500–600 ps for all fitting ions, respectively. The latter is assigned to a trans–cis photoisomerization process, which decreased in efficiency in the presence of partially fitting ions, i.e., increasing ion size. Steady state irradiation showed clear evidence of a change in the absorption spectra. Trans–cis photoisomerization and [2 + 2] photocycloaddition were found to compete with fluorescence. The ions Li⁺, Na⁺, and Ca²⁺, which fit into the cavity, direct the photoisomerization. Larger ions (K⁺, Rb⁺, Sr²⁺ and Ba²⁺) that partially fit the cavity cause photocycloaddition. Quantum yields of the photoreaction are between 0.1 and 0.3. Analysis of the photoproduct obtained for the 1-Sr²⁺ system revealed a compound with a molecular weight of nanosize dimension, which was equivalent to seven mass units of 1. The higher molecular weight product was formed due to alternately stacked supramolecular assemblies.

Keywords: CROWN ETHER; FLUORINE SUBSTITUTION; NANOMATERIAL; OLIGOPHENYLENEVINYLENES; PHOTOISOMERIZATION; PHOTOCYCLOADDITION; PPV; CHEMOSENSOR; ULTRAFAST TRANSIENT ABSORPTION; FLUORESCENCE; SOLVATOCHROMISM; OLIGOMERIZATION; NMR

Document Type: Research article

DOI: http://dx.doi.org/10.1166/jnn.2001.001

Affiliations: 1: Center for Photochemical Sciences and the Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, USA; Institute of Physical and Theoretical Chemistry, University of Potsdam, Karl Liebknecht Strasse 24/25, D-14476 Golm 2: Center for Photochemical Sciences and the Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, USA

Publication date: 2001-03-01

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• Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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