Enhancing Charge Transfer in (BIMCA)Pt(II) Alkynyls through the Use of Substituted Boranes

Organoboranes are commonly incorporated into ligands for luminescent molecules to expand conjugation pathways and impart Lewis acidity. Here, we report on the use of organoboranes to induce charge transfer from the luminescent core of bisimadazolylcarbazolide platinum­(II) alkynyls. The resulting donor–acceptor complexes are green-yellow phosphorescent emitters with low (<1%) quantum yield and microsecond lifetime in methylene chloride solution. In rigid PMMA film doped at 2% (w/w) the quantum yield significantly increases to 15–48% with lifetimes between 15 and 43 ms, suggesting a significant decrease in the rate of nonradiative decay in the rigid medium. TD-DFT calculations reveal that these complexes possess essentially HOMO–LUMO one-particle transitions to singlet excited states and their emission originates from a ligand/metal-to-ligand charge transfer (LMLCT) transition with the borane moiety as the electron acceptor. The observation of solvatochromism in the emission spectra supports a charge-transfer mechanism from the (BIMCA)Pt core through the alkynyl ligand to the borane substituents.