Consequences of the one-electron reduction and photoexcitation of unsymmetric bis-imidazolium salts.
Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+)  and unsymmetrical bis-imidazolium salts [6](2+)  and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+)  and [9](2+)  can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+)  and [9](.+)  undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+)  and [9](2+)  emit at room temperature in solution but with dramatically different characteristics. The different fluorescence behavior is analyzed by emission spectroscopy and interpreted by using time-dependent density functional calculations as largely due to different excited-state dynamics of [6](2+)  and [9](2+) . The geometries of both radicals [6](.+)  and [9](.+)  and excited states {[6](2+) }* and {[9](2+) }* are substantially different from those of the parent ground-state molecules.
Institute of Inorganic Chemistry, Eberhard Karls-University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
Verena
V
Gierz
Jascha
J
Melomedov
Christoph
C
Förster
Christine
C
Deissler
Frank
F
Rominger
Doris
D
Kunz
Katja
K
Heinze