Towards NIR emission in Pt(II)-cyclometallated compounds. From excimers formation to AIE.

Abstract

Two series of Pt(II) cyclometallated compounds containing N^C^N tridentate and alkynyl-chromophore as ligands have been synthesized and structurally characterized. The N^C^N ligands differ on the presence of R1 = H or F in the central aromatic ring while six different chromophores have been used attached to the alkynyl moiety. X-ray crystal structures were solved for some of the compounds and reveal the presence of weak intermolecular contacts responsible of the formation of some dimers or aggregates. The photophysical characterization show the presence of two emission bands in solution assigned to 3π-π* transition from the N^C^N ligands mixed with 3MLCT/3ILCT transitions (higher energy band) in deareated samples. The formation of excimers has been also identified as a broad band at longer wavelengths (near infrared-NIR emission) that becomes the main emission band for compounds containing phenanthrene as chromophore. NIR emission behavior has been also explored using acetonitrile:water mixtures and the presence of aggregates that emit at ca. 650 nm has been also detected.