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

The bifunctional aminopyridine ligands H2N-(CH2)n-4-C5H4N (n = 0, L1; 1, L2; 2, L3) have been utilized for the preparation of rhenium complexes [Re(phen)(CO)3(L1-L3)]+ (1-3). 2 and 3 with NH2-coordinated L2/L3 were coupled with cycloplatinated motifs {Pt(ppy)Cl} and {Pt(dpyb)}+ 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 the parentage to 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 the unconventional heteroleptic {Re(phen)}…{Pt(dpyb)} π-π stacking operates as a driving force for the 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.