Journal of Physical Chemistry & Biophysics
Open Access

Excited state lifetime of isolated iron(II) complexes and electron injection into TiO2 film

4^th International Conference on Physical and Theoretical Chemistry

September 18-19, 2017 Dublin, Ireland

Stefan Haacke

Universit�?© de Strasbourg, France

Keynote: J Phys Chem Biophys

Abstract :

Over last decades, transition metal complexes (Pt, Ir and Ru) have received great attention due to their long-lived electronic excited states, for applications such as OLEDs and dye-sensitized solar cells (DSSCs). However, the replacement of these expensive, scarce and toxic metals by earth-abundant metals such as Fe or Cu is still extremely challenging due to very short excited state lifetimes of the metal-to-ligand charge transfer states (MLCT), limited, in the case of Fe, by spin cross-over into metal-centered high spin states as observed in Fe-pyridine complexes. A possible way to stabilize the lowest energy triplet 3MLCT energetically and thus temporally is to increase the ligand field strength by chemical design. Recently, the use of N-heterocyclic carbenes (NHC) ligands was reported to lead to a prolonged 3MLCT lifetime (9 ps) which we were able to extend up to 16.5 ps due to carboxylation of the ligands (fig. A). Very recently, the W�?¤rnmark group working on the same carboxylated complex, reported efficient electron injection into TiO2 by using THz spectroscopy, but also deleterious charge recombination. We have designed new complexes where iron was coordinated by benzimidazolylidene-based (Biz) which affords a new record 3MLCT lifetime of 26 ps in MeCN. Streak camera fluorescence experiments on complexes grafted on TiO2 and Al2O3 substrates indicate electron injection through shorter 3MLCT state lifetime on TiO2 than on high-band gap Al2O3 (fig. B), but also surprisingly long 3MLCT state lifetime components induced only through binding on the semiconductor surfaces. A detailed modeling of the effect of surface attachment on the excited state ordering is in progress.

Biography :

Stefan Haacke is a Professor in Physics at Strasbourg University and Director of the Institute of Physics and Chemistry of Materials Strasbourg. His research on ultrafast spectroscopy of biologic molecules and organic nanostructures has been published in 114 papers. He is Coordinator of the French-German project Femto-ASR.