Gierz V, Melomedov J, Förster C, Deissler C, Rominger F, Kunz D, Heinze K. Consequences of the one-electron reduction and photoexcitation of unsymmetric bis-imidazolium salts.
Chemistry 2012;
18:10677-88. [PMID:
22791514 DOI:
10.1002/chem.201200323]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Revised: 05/11/2012] [Indexed: 11/10/2022]
Abstract
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.
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