Excited-State Switching in Rhenium(I) Bipyridyl Complexes with Donor-Donor and Donor-Acceptor Substituents

Joshua J Sutton; Dan Preston; Philipp Traber; Johannes Steinmetzer; Xue Wu; Surajit Kayal; Xue-Z Sun; James D Crowley; Michael W George; Stephan Kupfer; Keith C Gordon

doi:10.1021/jacs.1c02755

Excited-State Switching in Rhenium(I) Bipyridyl Complexes with Donor-Donor and Donor-Acceptor Substituents

J Am Chem Soc. 2021 Jun 23;143(24):9082-9093. doi: 10.1021/jacs.1c02755. Epub 2021 Jun 11.

Authors

Joshua J Sutton^{1

2}, Dan Preston^{1

2}, Philipp Traber³, Johannes Steinmetzer³, Xue Wu⁴, Surajit Kayal⁴, Xue-Z Sun⁴, James D Crowley^{1

2}, Michael W George^{4

5}, Stephan Kupfer³, Keith C Gordon^{1

2}

Affiliations

¹ Department of Chemistry, University of Otago, Dunedin 9016, New Zealand.
² MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6012, New Zealand.
³ Institute for Physical Chemistry, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany.
⁴ School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
⁵ Department of Chemical and Environmental Engineering, University of Nottingham Ningbo China, 199 Taikang East Road, Ningbo 315100 China.

PMID: 34111929
DOI: 10.1021/jacs.1c02755

Abstract

The optical properties of two Re(CO)₃(bpy)Cl complexes in which the bpy is substituted with two donor (triphenylamine, TPA, ReTPA₂) as well as both donor (TPA) and acceptor (benzothiadiazole, BTD, ReTPA-BTD) groups are presented. For ReTPA₂ the absorption spectra show intense intraligand charge-transfer (ILCT) bands at 460 nm with small solvatochromic behavior; for ReTPA-BTD the ILCT transitions are weaker. These transitions are assigned as TPA → bpy transitions as supported by resonance Raman data and TDDFT calculations. The excited-state spectroscopy shows the presence of two emissive states for both complexes. The intensity of these emission signals is modulated by solvent. Time-resolved infrared spectroscopy definitively assigns the excited states present in CH₂Cl₂ to be MLCT in nature, and in MeCN the excited states are ILCT in nature. DFT calculations indicated this switching with solvent is governed by access to states controlled by spin-orbit coupling, which is sufficiently different in the two solvents, allowing to select out each of the charge-transfer states.