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

5 years ago

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

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

The bifunctional aminopyridine ligands H2N-(CH2)n-4-C5H4N (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 3MLCT {Re}-based emission at 298 K, which changes to the 3IL(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. That's unusual! Four aminopyridine-bridged bimetallic Re–Pt dyads have been synthesized. A study of their photophysical properties, supported by TD-DFT calculations, have revealed an unconventional tendency to form bimolecular aggregates through heteroleptic {Re(phen)}⋅⋅⋅{Pt(dpyb)} π–π stacking interactions (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701539