Linking ReI and PtII Chromophores with Aminopyridines: A Simple Route to Achieve a Complicated Photophysical Behavior

Kristina S Kisel; Alexei S Melnikov; Elena V Grachova; Pipsa Hirva; Sergey P Tunik; Igor O Koshevoy

doi:10.1002/chem.201701539

Linking Re^I and Pt^II Chromophores with Aminopyridines: A Simple Route to Achieve a Complicated Photophysical Behavior

Chemistry. 2017 Aug 22;23(47):11301-11311. doi: 10.1002/chem.201701539. Epub 2017 Jul 27.

Authors

Kristina S Kisel^{1

2}, Alexei S Melnikov³, Elena V Grachova², Pipsa Hirva¹, Sergey P Tunik², Igor O Koshevoy¹

Affiliations

¹ Department of Chemistry, University of Eastern Finland, Yliopistokatu 7, Joensuu, Finland.
² Institute of Chemistry, St.-Petersburg State University, 26 Universitetskiy pr., Petergof, St. Petersburg, Russia.
³ Peter the Great St.-Petersburg Polytechnic University, Polytechnicheskaya, 29, St. Petersburg, Russia.

PMID: 28636113
DOI: 10.1002/chem.201701539

Abstract

The bifunctional aminopyridine ligands H₂ N-(CH₂ )_n -4-C₅ H₄ N (n=0, L1; 1, L2; 2, L3) have been utilized for the preparation of the rhenium complexes [Re(phen)(CO)₃ (L1-L3)]⁺ (1-3; phen=phenanthroline). Complexes 2 and 3 with NH₂ -coordinated L2 and L3, respectively, were coupled with cycloplatinated motifs {Pt(ppy)Cl} and {Pt(dpyb)}⁺ (ppy=2-phenylpyridine, dpyb=dipyridylbenzene) to give the bimetallic species [Re(phen)(CO)₃ (μ-L2/L3)Pt(ppy)Cl]⁺ (4, 6) and [Re(phen)(CO)₃ (μ-L2/L3)Pt(dpyb)]²⁺ (5, 7). In solution, complexes 4 and 6 show ³ MLCT {Re}-based emission at 298 K, which changes to the ³ IL(ppy) state at 77 K. The photophysical properties of compounds 5 and 7 display a pronounced concentration dependence, presumably due to the formation of bimolecular aggregates. Analysis of the spectroscopic data, combined with TD-DFT simulations, suggest that unconventional heteroleptic {Re(phen)}⋅⋅⋅{Pt(dpyb)} π-π stacking operates as the driving force for ground-state association. The latter, together with intra- and intermolecular energy-transfer processes, determines the appearance of multiple emission bands and results in nonlinear relaxation kinetics of the excited states.

Keywords: heterometallic complexes; luminescence; platinum; rhenium; stacking interactions.