Multichromophoric arrays arranged around a triptycene scaffold: synthesis and photophysics

Here we report on the synthesis, characterization, and photophysics of multichromophoric arrays based on a triptycene scaffold that acts as a bridging ligand for Ir(III) and Os(II) satellite active components. The triptycene scaffold not only furnishes a rigid star-shaped 3D displacement of the metallic units in space but also plays an active role in the energy cascade. The transition metal complexes have been designed in order to display an ideal cascade in their lowest excited state energy levels. For this purpose, a novel Ir(III) complex containing two dbpz (dibenzo[a,c]phenazine) ligands (Ir) has been synthesized. The key step in the synthesis of the array was the final cross-coupling between the mixed complex IrF-Os and Ir, providing the target heterotrinuclear complex IrF-Ir-Os. The photophysical properties of models confirmed the appropriate energy displacement of the single chosen active units, in the order triptycene > IrF > Ir > Os, and fast and efficient energy transfer processes leading to the final population of the Os-based triplet level have been evidenced. The reported arrays can be considered as efficient antenna systems with an absorption range extending up to 700 nm, where the triptycene bridging ligand provides both a structural and a photophysical function.