Luminescent platinum(II) bis(1,1-dithiolate) complexes

Abstract

The bis(1,1-dithiolate) complexes (TBA)2[Pt(ecda)2], (TBA)2[Pt(i-mnt)2] and (PPN)2[Pt(ecda)2], where TBA = tetra-n-butylammonium, ecda = 1-(ethoxycarbonyl)-1-cyanoethylene-2,2-dithiolate, i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and PPN = bis(triphenylhosphoranylidene)ammonium, have been prepared and their photoluminescent properties have been investigated. Intense emission is observed in frozen solvent glasses and in the solid state at 77 K, but not in fluid solution at 298 K. The emission is assigned to a charge-transfer-to-dithiolate phosphorescence, involving an excited state having the same orbital parentage as the strongly allowed, low energy charge-transfer band in the absorption spectrum. The counter-ion influences the energy of the charge-transfer absorption and emission bands slightly but significantly as a result of weak ion-pairing that occurs in solution. Photolysis with λ < 360 nm in halocarbon solvents leads to irreversible photooxidation of the complex, presumably via a charge transfer-to-solvent excitation. The photochemically promoted oxidation does not occur upon longer wavelength irradiation (λ > 400 nm) and therefore does not arise from the emissive excited state of the complex.