Unusually Strong Electrochemiluminescence from Iridium-Based Redox Polymers Immobilized As Thin Layers or Polymer Nanoparticles

Abstract

A new class of redox metallopolymer based on cyclometalated iridium(III) centers is described, with unusually intense luminescence properties in aqueous media. We report the facile synthesis, photophysical and electrochemical characterization, supported by DFT calculations and their electrochemiluminescence (ECL) properties which, under some circumstances, are significantly greater than the analogous ruthenium-based materials. The photoluminescence (PL) and ECL of these materials are further dramatically enhanced when dispersed or immobilized as polymeric nanoparticles (PNPs). This aggregation-induced emission (AIE and AIECL) operates by providing important protection for the cyclometalated iridium(III) centers against the types of quenching processes which commonly afflict iridium-based luminophores in aqueous media. The results suggest interesting new avenues of research for the application of such materials in and PL and ECL-based detection and imaging as well as light-emitting devices.

Metallopolymers as Nanostructured Solid‐State Platforms for Electrochemiluminescence Applications

“…Iridium(III) has been also integrated into polymers, as pendants of a polyvinylpyridine/polystyrene (PVP:PS) backbone for ECL applications . Recently, Hogan and co‐workers developed a strategy to achieve enhanced emission of Ir III based materials in aqueous media through the formation of polymeric nanoparticles (PNPs) . These metallopolymers bearing phosphorescent complexes of general formula [Ir(C N) 2 (PVP/S) 2 ] + , where C N is a cyclo‐metalating ligand such as 2‐phenylpyridine or 2‐(2,4‐difluorophenyl)pyridine, have been easily synthesized by following well‐established synthetic routes.…”

“…A similar concept of encapsulation of emitters within PNPs has been employed to prepare a copolymer with two different iridium centers. This strategy resulted in a functional material which sensitize through energy transfer the ECL emission of the metal center with lower‐energy emission with an enhancement by up of five times compared with metallopolymers containing only one type of iridium center . The energy transfer occurs following electrochemical excitation (ECL‐ET) of PNPs.…”

“…In a similar manner, the synthetic pathway entailed refluxing of Os(bpy) 2 Cl 2 with an excess of PVP in ethanol, with a subsequent filtration and precipitation to obtain the perchlorate salt via metathesis reaction. [58][59][60] Notably, the synthesis of PVP based polymers containing photo-and electro-active cyclo-metalated iridium complexes is particularly straightforward, as recently shown by Hogan et al [32,33] Indeed, these metallopolymers are rapidly formed by simply mixing the coordinating polymer with a dichloro-bridged iridium dimer precursor at room temperature. Scheme 1.…”

“…Metallopolymers are a very attractive class of hybrid materials that contain metal ions within a polymeric architecture . ECL‐active metallopolymers are suitable for the fabrication of biosensors due to the ease of deposition and relatively easy synthesis . These polymers find use in numerous application such as electrocatalysis, electrochromic devices, sensors, actuators, energy storage, and energy‐harvesting as extensively reported by different reviews on this topic …”

“…[28] ECL-active metallopolymers are suitable for the fabrication of biosensors due to the ease of deposition and relatively easy synthesis. [29][30][31][32][33] These polymers find use in numerous application such as electrocatalysis, [34,35] electrochromic devices, [36] sensors, [37] actuators, [38,39] energy storage, [40] and energy-harvesting [41] as extensively reported by different reviews on this topic. [28,[42][43][44][45][46] This Concept article aims at illustrating the use of metallopolymers in ECL by presenting and discussing some selected key examples in this growing area of research.…”