J. Phys. Chem. A 2001, 105, 5655-5665
5655
Competition between Conformational Relaxation and Intramolecular Electron Transfer within Phenothiazine-Pyrene Dyads† J. Daub,*,‡ R. Engl,‡ J. Kurzawa,§ S. E. Miller,| S. Schneider,*,§ A. Stockmann,§ and M. R. Wasielewski*,| Institut fu¨ r Organische Chemie, UniVersita¨ t Regensburg, D-93040 Regensburg, Germany, Institut fu¨ r Physikalische und Theoretische Chemie, Friedrich-Alexander-UniVersita¨ t Erlangen-Nu¨ rnberg, D-91058 Erlangen, Germany, and Department of Chemistry, Northwestern UniVersity, EVanston, Illinois 60208- 3113 ReceiVed: October 12, 2000; In Final Form: February 1, 2001
The competition between conformational dynamics and electron transfer within a series of phenothiazine(phenyl)n-pyrene (n ) 0, 1) electron donor-acceptor dyads of potential use in organic light emitting diodes was examined using femtosecond transient absorption spectroscopy. The molecular structures of these dyads permit only torsional motions around the single bonds joining each aromatic subunit. The redox properties of these molecules are nearly independent of the phenyl bridging group, whereas spectroelectrochemistry shows that the UV/vis absorption spectra of the oxidized and reduced species vary with the bridge. Each molecule exhibits dual fluorescence emission which provides evidence for conformational heterogeneity. Emission from a locally excited state originates from a minority conformation, in which electron transfer is negligible, whereas emission because of ion pair recombination results from the majority conformation which undergoes electron transfer. The electron-transfer reactions proceed with time constants
