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

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.