Published on Web 10/27/2007
Effects of Bay Substituents on the Racemization Barriers of
Perylene Bisimides: Resolution of Atropo-Enantiomers
Peter Osswald and Frank Wu¨rthner*
Contribution from the Institut fu¨r Organische Chemie, UniVersita¨t Wu¨rzburg, Am Hubland,
97074 Wu¨rzburg, Germany
Received June 20, 2007; E-mail: wuerthner@chemie.uni-wuerzburg.de
Abstract: The activation parameters for the interconversion of atropisomers (P- and M-enantiomer) of core-
twisted perylene bisimides have been determined by dynamic NMR spectroscopy (DNMR) and time- and
temperature-dependent CD spectroscopy. By comparing the activation parameters of a series of perylene
bisimides containing halogen or aryloxy substituents in the bay area (1,6,7,12-positions), a clear structure-
property relationship has been found that demonstrates that the kinetic and thermodynamic parameters
for the inversion of enantiomers are dependent on the apparent overlap parameter ∑r* of the bay
substituents. This study reveals a high stability (∆Gq
) 118 kJ/mol) for the atropo-enantiomers of
368
K
tetrabromo-substituted perylene bisimide in solution. Accordingly, the enantiomers of this derivative could
be resolved by HPLC on a chiral column. These enantiomers do not racemize in solution at room temperature
and, thus, represent the first examples of enantiomerically pure core-twisted perylene bisimides.
Introduction
for organic and polymeric light-emitting diodes (OLEDs and
PLEDs), organic field-effect transistors (OFETs), and solar
In recent years, bay-functionalized perylene bisimides (PBIs)
have received considerable attention for a wide range of
applications, for example, as fluorescent dyes for single molecule
spectroscopy1 and bio-imaging2 and as organic semiconductors
cells.3 The molecular properties that enable all these applications
are the high fluorescent quantum yield, fairly persistent radical
anion state, easy accessibility, and outstanding stability of these
dyes against environmental influences.4 For most of the ap-
plications, aryloxy-, cyano-, or pyrrolidino-substituted PBIs have
been employed, whereas the readily available halogen-substi-
tuted PBIs, such as 1,7-dibromo and 1,6,7,12-tetrachloro deriva-
tives, have been used as intermediates for the synthesis of these
functionalized perylene bisimides.4 In the past few years, the
utility of tetrahalogen-substituted PBIs, especially the tetrachloro
derivatives, has also been demonstrated for a variety of
applications, for example, as organic semiconductor;5 in mul-
tichromophoric systems containing tetrathiafulvalene,6 fullerenes,7
or oligo(phenylenevinylene)s;8 and as liquid crystals,9 laser
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10.1021/ja074508e CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 14319-14326
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