Cyclometalated NHCs Pt(II) Compounds with Chelating P∧P and S∧S Ligands: From Blue to White Luminescence

Ionic [Pt(C boolean AND C*(A/B))(P boolean AND P)]PF6 and neutral [Pt(C boolean AND C*(A/B))(S boolean AND S)] complexes were designed and synthesized containing cyclometalated N-heterocyclic carbenes (C boolean AND C*(A/B)) and diphosphines (P boolean AND P: dpfppe, dcypm) or dithiocarbamates (S boolean AND S: dmdtc, pdtc) as chelating ligands. Their structural and spectroscopic properties were investigated and found to be dependent on both cyclometalated (C boolean AND C*(A/B)) and ancillary (P boolean AND P, S boolean AND S) ligands. The photophysical and computational studies for the [Pt(C boolean AND C*(A/B))[(Pt(C boolean AND C*A/B) (P boolean AND P)](+)complexes disclose the nature of the low-lying electronic transitions to be mainly intraligand charge transfer [ILCT (C boolean AND C*(A/B))] with some contribution of ligand-to-ligand charge transfer (LL'CT) or ligand-to metal charge transfer (LMCT) for the dpfppe or dcypm derivatives, respectively. The blue and cyan emissions of PMMA films doped with the [Pt(C boolean AND C*(A/B))]/B)(P boolean AND P](+) complexes exhibited very high quantum yields (QYs) reaching up to similar to 90%. However, the low-energy absorptions and emissions of the [Pt(C boolean AND C*(A/B))(S boolean AND S)] complexes in solution (rt or 77 K) arise from mixed ILCT [C boolean AND C*(A/B)]/MLCT [d pi(Pt) -> pi *(C boolean AND C*(A/B))] excited states, showing no change with the different S boolean AND S ligands. In solid-state and in doped films, these dithiocarbamate complexes, excluding 8B, display dual emissions with the high-energy vibronic band ((ILCT)-I-3/(MLCT)-M-3) appearing together with an additional low-energy structureless band. The latter is attributed to (3)pi pi* transitions originated from pi-stacked aggregates, as reported in the X-ray structure of 7A. Thus, white light emissions can be obtained with photo- and colorimetric values lying inside the stipulated limits for general lighting applications; yet, they display low QY.