Photoluminescent Pt(II) and Pd(II) complexes [M(diphosphine)(btdt)] of the 2,1,3-benzothiadiazole-5,6-dithiolate ligand

Abstract

We study luminescent properties of complexes with 2,1,3-benzothiadiazole-5,6-dithiolate (btdt²⁻) that combines chromophore heterocyclic unit and chelating thiolate groups. A series of new heteroligand complexes with the general formula [M(dppx)(btdt)] were chosen (M = Pt, Pd; dppx = diphenylphosphinomethane (dppm), diphenylphosphinoethane (dppe) and diphenylphosphinoethilene (dppen). Combined experimental and TD-DFT studies reveal negligible effect of the diphosphine ligands on the absorption spectra of the complexes in the solid state and solutions. The first non-dark absorption band at 410–430 nm is attributed to an intraligand (localized on btdt moiety) transition with a minor contribution of a metal–to–ligand charge transfer. In solid state, all complexes exhibit vibrationally-resolved phosphorescence at room temperature in the range of 650–800 nm with a large Stokes shift of ca. 8800 cm⁻¹, and with the observed lifetimes of the excited state of 5–110 μs. The presence of an emission signal for [Pd(dppx)(btdt)] is a rare case of room-temperature phosphorescent Pd complexes. In the THF solutions under an argon atmosphere, only the Pt complexes reveal luminescent signal peaked at 650–800 nm, which is quenched upon contact with air.