Homoleptic tris-cyclometalated platinum(iv) complexes: a new class of long-lived, highly efficient ³LC emitters

Abstract

Tris-cyclometalated Pt(IV) complexes are reported for the first time. The facial isomers exhibit long-lived 3LC emissions with quantum yields up to 0.49, the highest ever found for Pt(IV) complexes, combined with a strong oxidizing character in the excited state.

Exploring Excited‐State Tunability in Luminescent Tris‐cyclometalated Platinum(IV) Complexes: Synthesis of Heteroleptic Derivatives and Computational Calculations

“…To illustrate this, the absorption spectra of mer ‐ 3 ac and mer ‐ 3 ad are compared in Figure 3 with those of 2 a and 2 c , or 2 a and 2 d , respectively, which can be taken as representative of the absorptions of each cyclometalating ligand. The absorption bands of fac ‐ 3 ab are sharper and of slightly higher energies compared with mer ‐ 3 ab , just as observed for the homoleptic derivatives mer / fac ‐ 3 a and b 15. None of the complexes exhibit solvatochromic absorptions, which suggests that the involved electronic transitions have little or no charge‐transfer character.…”

“…We have previously shown that the reactions of bis‐cyclometalated precursors of the type [Pt(C^N) 2 Cl 2 ] with AgOTf (2 equiv) and an excess of the N^CH ligand in non‐coordinating solvents give mer isomers of homoleptic tris‐cyclometalated Pt IV complexes mer ‐[Pt(C^N) 3 ]OTf (C N=ppy, tpy, dfppy, ppz) (Scheme ) 15. The corresponding strongly emissive fac isomers were obtained by photoisomerization.…”

“…Following the synthetic route used for the homoleptic complexes,15 we carried out irradiations of dilute acetonitrile solutions of the heteroleptic mer complexes with UV light to obtain the corresponding fac isomers through photoisomerization. Complex mer ‐ 3 ab cleanly isomerized to fac ‐ 3 ab in good yield (see Supporting Information for details).…”

“…Although cyclometalated Pt IV complexes fall into this category, studies on their excited‐state properties are very limited,13 probably because of the intense focus on Pt II systems, which has yielded impressive results 14. Recently, we have reported the synthesis of a series of meridional and facial isomers of homoleptic tris‐cyclometalated Pt IV complexes, mer/fac ‐[Pt(C^N) 3 ] + , containing C ‐deprotonated 2‐phenylpyridine (ppy), 2‐( p ‐tolyl)pyridine (tpy), 2‐(2,4‐difluorophenyl)pyridine (dfppy), or 1‐phenylpyrazole (ppz) as ligands 15. The facial isomers exhibit high‐energy (blue) emissions from 3 LC states, characterized by lifetimes in the hundreds of microseconds range and quantum yields up to 0.49 in fluid solution at room temperature.…”

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

“…The complexes contained bis-cyclometalating (C^N) ligands of the general formula Pt(C^N) 2 (CH 2 Cl)Cl and were prepared by a photooxidative addition of CH 2 Cl 2 onto the corresponding bis-cyclometalated Pt(II) parental complexes. Although Pt(IV) complexes have attracted great attention in cancer therapy [104–106], only in the very recent past they are receiving increasing interest as luminescent compounds [107–108]. Such derivatives are characterized by long-lived triplet-manifold π–π* excited states with either 3 LC or 3 ILCT nature.…”