Issue 25, 2021

Transient FTIR spectroscopy after one- and two-colour excitation on a highly luminescent chromium(iii) complex

Abstract

The development of photoactive transition metal complexes with Earth-abundant metals is a rapidly growing research field, where a deeper understanding of the underlying photophysical processes is of great importance. A multitude of potential applications in the fields of photosensitizing, optical sensing, photoluminescence and photoredox catalysis motivates demanding spectroscopic studies. We applied a series of high-level spectroscopic methods on the previously reported highly luminescent chromium(III) complex [Cr(ddpd)2](BF4)3 (ddpd = N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine) possessing two near-IR emissive doublet states with microsecond lifetimes. Luminescence measurements were performed at temperatures down to about 10 K, showing a remarkable rise of the integrated emission intensity by more than a factor of three. The emissive doublet states were structurally characterized by transient FTIR spectroscopy at 290 K and 20 K, supplemented by ground state FTIR and Raman spectroscopy in combination with density functional theory. According to emission and step-scan FT-IR spectroscopy, the stronger luminescence at lower temperature arises from decreased non-radiative decay via energy transfer to CH vibrational overtones and increased radiative decay based on lowered symmetry. Pump/pump/probe (FTIR) and pump/dump/probe (FTIR) schemes were developed to modulate the excited doublet state populations at 290 and 20 K as a function of specific near-IR pump vs. dump wavelengths. The effect of the second near-IR pulse can be explained by combinations of excited state absorption, ground state absorption and stimulated emission. The successful establishment of these two-colour step-scan FTIR experiments is an important step towards profound studies on further transition metal complexes with energetically close-lying excited states in the near future.

Graphical abstract: Transient FTIR spectroscopy after one- and two-colour excitation on a highly luminescent chromium(iii) complex

Supplementary files

Article information

Article type
Paper
Submitted
10 Mar 2021
Accepted
10 Jun 2021
First published
10 Jun 2021

Phys. Chem. Chem. Phys., 2021,23, 13808-13818

Transient FTIR spectroscopy after one- and two-colour excitation on a highly luminescent chromium(III) complex

P. Boden, P. Di Martino-Fumo, G. Niedner-Schatteburg, W. Seidel, K. Heinze and M. Gerhards, Phys. Chem. Chem. Phys., 2021, 23, 13808 DOI: 10.1039/D1CP01077H

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