Molecularly Engineered Near‐Infrared Light‐Emitting Electrochemical Cells

Abstract

The development of near‐infrared (NIR) luminescent materials has emerged as a promising research field with important applications in solid‐state lighting (SSL), night‐vision‐readable displays, and the telecommunication industry. Over the past two decades, remarkable advances in the development of light‐emitting electrochemical cells (LECs) have stunned the SSL community, which has in turn driven the quest for new classes of stable, more efficient NIR emissive molecules. In this review, an overview of the state of the art in the field of near‐infrared light‐emitting electrochemical cells (NIR‐LEC) is provided based on three families of emissive compounds developed over the past 25 years: i) transition metal complexes, ii) ionic polymers, and iii) host–guest materials. In this context, ionic and conductive emitters are particularly attractive since their emission can be tuned via molecular design, which involves varying the chemical nature and substitution pattern of their ancillary ligands. Herein, the challenges and current limitations of the latter approach are highlighted, particularly with respect to developing NIR‐LECs with high external quantum efficiencies. Finally, useful guidelines for the discovery of new, efficient emitters for tailored NIR‐LEC applications are presented, together with an outlook towards the design of new NIR‐SSL materials.

Near‐Infrared Emission by Tuned Aggregation of a Porphyrin Compound in a Host–Guest Light‐Emitting Electrochemical Cell

“…[10b-d,13a,15] Recently, it was also demonstrated that well-designed host-guest LEC devices can deliver strong luminance at high efficiency. [16] A recent review by Pilkington et al [19] nicely summarized the current status of NIR-emitting LEC devices. The majority of NIR-emitting LECs to date comprise ionic transition metal complexes (iTMCs) based on Ru [17] and Ir [7c] as the emitter, although NIR-emitting LECs based on Os [18] have also been reported.…”

“…A recent review by Pilkington et al. [ 19 ] nicely summarized the current status of NIR‐emitting LEC devices. The majority of NIR‐emitting LECs to date comprise ionic transition metal complexes (iTMCs) based on Ru [ 17 ] and Ir [ 7c ] as the emitter, although NIR‐emitting LECs based on Os [ 18 ] have also been reported.…”

New molecularly engineered binuclear ruthenium(ii) complexes for highly efficient near-infrared light-emitting electrochemical cells (NIR-LECs)

“…It is further noted that most iTMC-based NIR-LECs still suffer from limited device efficiencies due to unfavorable radiative transition at lower emission energies. 48,80,81 (see Tables S2 and S3, ESI †). However, in this new molecular engineered approach, the methylene groups act as a spacer, separating the two metal emitting centers which prevents intermolecular π-π stacking interactions between the two metal centers, leading to a reduction of the self-quenching and an increase of the efficiency of the device as confirmed by the measurement of the PLQY in neat-films.…”

“…[42][43][44][45][46] Moreover it is worth noting that although a large number research studies have been focused on the chemical modifications of iTMC-emitters, only a few reports have been devoted to investigating the turn-on time and stability of near-infrared light-emitting electrochemical cells (NIR-LECs). 47,48 In light of all the aforementioned facts, here we designed and synthesized three novel binuclear heteroleptic Ru(II) complexes as near-infrared emitters based on the bridging phenanthroimidazole (PI) ligand containing two pyridine moieties (Scheme 1), namely, D1, D2, and D3. The structural, electrochemical, and photophysical properties of these three emitters were fully characterized to understand their potential and they were then tested in NIR-LEC devices.…”

BODIPY‐Pt‐Porphyrins Polyads for Efficient Near‐Infrared Light‐Emitting Electrochemical Cells

“…[3,[6][7][8] While several red emitters have already been implemented in LECs, [1,3,[9][10][11][12][13][14][15][16][17][18][19][20] the best NIR-emitting LECs rely on ionic transition metal complexes. [9,[21][22][23][24][25][26][27] Here, porphyrins could stand out due to their easy synthesis and modification toward NIR emission. [28] Indeed, several groups have recently shown interesting advances in porphyrin-based LECs.…”