Anion(I–)–π(bisphosphonium)2+ photoluminescence enhanced by [Pt(CN)2(Me-phpy)]–

Abstract

A major challenge in luminescent materials is inefficient energy utilization, where a substantial fraction of absorbed energy is dissipated through non-radiative pathways. This limitation can be addressed at the molecular level by rational design of emissive systems. Combining suitable chromophores and/or supporting frameworks allows control over crystal packing, spin–orbit coupling and heavy-atom effects, as well as intermolecular energy transfer, thereby minimizing energy losses and enhancing emission efficiency of phosphorescence. In this context, we present structural and photoluminescence properties of a new hybrid organic–inorganic composite salt [1,4-nap(PMePh₂)₂][Pt(CN)₂(Me-phpy)][I]·2MeCN (1) that integrates two previously recognized chromophores: the bisphosphonium–iodide fragment featuring anion–π interactions and the cycloplatinated anion. Photophysical analysis supported by TD-DFT calculations shows that the emission originates from the triplet charge transfer (CT) excited state ³(iodide → π*) (T₁) localized within an anion–π ion pair. Composite 1 exhibits a room temperature phosphorescence quantum yield of 0.19, featuring nearly twofold enhancement compared to the precursor bisphosphonium iodide salt. This is attributed to the synergy of suppressed non-radiative decays and enhanced population of the emissive T₁ state via triplet–triplet energy transfer (TTET) from its platinum counterpart. These results were achieved owing to the grafting of the [bisphosphonium]–[I⁻] supramolecular anion–π adduct into 1, demonstrating a strategic approach towards improved photoluminescence in molecular materials.