Session: Electrochemistry in Organic Synthesis:

The search for deep-red and near-infrared (NIR) small molecule emitters for solid-state lighting devices is an ongoing quest. Among the solid-state lighting approaches, light-emitting electrochemical cells (LECs) are of particular interest. While several red emitters have been implemented in LECs, porphyrins stand out due to their easy synthesis and modification. In 2016, our group firstly reported on the effect of the metal core of porphyrins on the LEC figures-of-merit, achieving red-emitting devices that were either stable (Zn-porphyrin) or highly efficient (Pt-por[hyrin). Low stability can be overcome using a host-guest system to decouple charge transport and exciton recombination. For instance, we reported on intramolecular host-guest systems binding one BODIPY (BDP) unit to the periphery of a Zn-por, that yielded deep-red LECs with 1 order of magnitude enhanced stabilities (>1,000 h).
Herein, we present the design of two NIR emitting Pt-porphyrins (Pt-por) with none and 20 F-atoms and their respective Pt-por-polyads containing from 1 to 4 BDP units (PtBDP) connected via tetra-fluorophenyl triazole spacer groups. The functionalization of PtBDPs was tuned in order to optimize: i) the NIR emission through an efficient energy transfer from the BDP to the Pt-por core, ii) the electronic structure to decouple charge transport via BDP and exciton formation at the Pt-por, and iii) the ionic conductivity in thin films. Using these parameters, we prepared LECs with emission centered at 780 nm associated to irradiances (>80 μW/cm²) and efficiencies (0.12 lm/W) that are among the best reported. This was realized using PtBDP bearing 2 BDP units and 8 F atoms, in which a host:guest strategy between BDP and Pt-por in thin films is fully operative for both energy and charge transfer processes, accompanied by an optimal ionic conductivity. Overall, this work highlights that Pt-por-based systems are very interesting emitters to develop NIR LECs.

Luca Maria Cavinato

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