Determining the Quintet Lifetimes in Side-ring Substituted [Fe(terpy)2]2+ Complexes

Authors

  • Andor Vancza
    Affiliation
    Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary
    Department of Physical Chemistry and Materials Science, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Műegyetem rkp. 3, H-1111 Budapest, Hungary
  • Marcell Levente Kapta
    Affiliation
    Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary
  • Mariann Papp
    Affiliation
    Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary
  • György Vankó
    Affiliation
    Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary
  • Tamás Keszthelyi
    Affiliation
    Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary
https://doi.org/10.3311/PPch.22748

Abstract

We previously studied the effect of 4' substitution in iron(II)-bis-terpyridine complexes, showing that the photoexcited high-spin quintet-state is stabilized by electron-donating substituents. In this paper we explore the effects of electron-donating ( X = NH2 , Cl ) and withdrawing ( X = NO2 ) substituents in the 5,5" positions on the stability and lifetime of the quintet-state. We used a simple densitiy-functional theory (DFT) based method that had been proven fairly accurate in the case of 4' substitution to estimate the energy barrier of the quintet-singlet transition and thereby predict the quintet state lifetime. We synthetized the complexes and used ultrafast transient optical absorption spectroscopy to experimentally determine the quintet lifetimes, in order to test the applicability of these quantum-chemistry based predictive methods for these side-ring substitution cases. UV-Visible spectra of the complexes have shown that the metal-to-li­gand charge transfer (MLCT) and ligand-localized transitions of these complexes change according to the previous observations. We have shown that in the 5,5" positions, electron withdrawing groups stabilize the quintet state, while donating groups destabilize it. This is in stark contrast to the effects previously observed for the 4' case, and indicates that unlike the latter case, the simple concept of inductive and mesomeric effects may not be adequate to describe the changes due to 5,5" substitution, warranting further study of the area.

Keywords:

coordination complexes, iron, substituent effects, spin state transition, molecular engineering, terpyridine, transient absorption spectroscopy, pump-probe spectroscopy

Citation data from Crossref and Scopus

Published Online

2023-11-16

How to Cite

Vancza, A., Kapta, M. L., Papp, M., Vankó, G., Keszthelyi, T. “Determining the Quintet Lifetimes in Side-ring Substituted [Fe(terpy)2]2+ Complexes”, Periodica Polytechnica Chemical Engineering, 67(4), pp. 547–556, 2023. https://doi.org/10.3311/PPch.22748

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