Controlling the emission in flexibly-linked (N^C^N)platinum dyads

Abstract

The synthesis, spectroscopic and theoretical characterizations of dinuclear Pt(II) complexes where the two chromophoric units are connected though a polyether chain via either the central benzene ring of the tridentate ligand dpyb (Pt-2), or the phenylacetylide ligand (Pt-3), are described. The spacer, which contains four oxyethylene –CH₂CH₂O– units, is flexible and long enough to allow a self-association of the Pt units by folding, as shown by DFT calculations. Comparison of the photophysical properties of the dinuclear complex Pt-2 with those of the mononuclear complex Pt-1, used as reference, demonstrates the key role played by the linker group in the interaction processes. In addition, the emission of complex Pt-2 was found to be affected by the temperature, nature of the solvent, and cation coordination as evidenced by luminescence and ¹H NMR studies. The interacting processes are highly dependent on the solvent polarity that controls the – extended vs folded – arrangement and, consequently, induces solvatochromic shifts. This unique photophysical behavior of Pt-2 allows the modulation of the emission from green to deep-red (up to 125 nm) over the visible part of the spectrum. By contrast, complex Pt-3 has a high propensity to form a red-shifted intense emissive excimer. DFT and TD-DFT investigations of the excimers in Pt-2 and Pt-3 consistently show a much stronger interaction in the latter complex.