Extreme Tuning of Redox and Optical Properties of Cationic Cyclometalated Iridium(III) Isocyanide Complexes

Shavaleev, Nail M.; Monti, Fiorella; Scopelliti, Rosario; Baschieri, Andrea; Sambri, Letizia; Armaroli, Nicola; Grätzel, Michaël; Nazeeruddin, Mohammad Khaja

doi:10.1021/om300894m

Cited by 49 publications

(60 citation statements)

References 65 publications

(146 reference statements)

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“…The more intense ε values found for 1a and 2a are due to the extended benzimidazole aromatic moieties on the carbene subunits of the ancillary ligands. The structureless bands at 300−360 nm can be assigned both to phenyl-topyridine π−π* ligand-to-ligand (interligand) charge transfer (LLCT) transitions and to Ir(d π )-to-phenylpyridine MLCT (12) 168.56 (7) 168.86 (13) 170.40 (17) 168.11 (9) 171.31 (18) transitions with a predominant singlet spin multiplicity. 11 The lower-lying bands in the visible region (>360 nm) can be attributed to both singlet and triplet MLCT transitions, which, however, have a strong π−π* character.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

et al. 2013

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Charged cyclometalated (C(^)N) iridium(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C(^)N ligands, in contrast to the classical design of charged complexes where N(^)N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C(^)N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C(^)C:) and four different pyridine-carbene (N(^)C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C(^)C: complexes show much larger photoluminescence quantum yields (ΦPL) of ca. 30%, compared to the N(^)C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly(methyl methacrylate) matrix, ΦPL 30-60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N(^)C:-type complexes possess a low-lying triplet metal-centered ((3)MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C(^)C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N(^)C: and :C(^)C: complexes.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

et al. 2013

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“…General procedure for the synthesis of [Ru(C^N)(L aux )(bpy(CO 2 H) 2 )](PF 6 ). 1 The [Ru(C^N)(L aux )(bpy(CO 2 Me) 2 )](PF 6 ) was dissolved in 5 ml of DMF:H 2 O:NEt 3 (3:1:1) and reaction mixture was refluxed for one day under nitrogen.…”

Section: S18mentioning

confidence: 99%

“…1 The [Ru(C^N)(L aux )(bpy(CO 2 Me) 2 )](PF 6 ) was dissolved in 5 ml of DMF:H 2 O:NEt 3 (3:1:1) and reaction mixture was refluxed for one day under nitrogen. Afterwards, the reaction mixture was extracted with dichloromethane and washed with 0.1 % aqueous HPF 6 solution.…”

Section: S18mentioning

confidence: 99%

“…1 As an alternative to conventional solar cells, third-generation photovoltaic devices with dye-sensitized solar cells (DSCs) at the forefront have been extensively studied. 2 In standard DSCs, mesoporous TiO 2 is sensitized by a ruthenium(II) complex or an organic dye, and I 3 − /I − is widely employed as the most effective redox couple. 3,4 Congruence between the dye molecule chemisorbed on a mesoporous oxide and redox pair in the electrolyte in DSCs should be fine-tuned to obtain fast dye regeneration and ideally slow charge recombination.…”

Section: ■ Introductionmentioning

confidence: 99%

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Ligand Engineering for the Efficient Dye-Sensitized Solar Cells with Ruthenium Sensitizers and Cobalt Electrolytes

Aghazada

Gao

Yella³

et al. 2016

Inorg. Chem.

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Over the past 20 years, ruthenium(II)-based dyes have played a pivotal role in turning dye-sensitized solar cells (DSCs) into a mature technology for the third generation of photovoltaics. However, the classic I 3 − /I − redox couple limits the performance and application of this technique. Simply replacing the iodine-based redox couple by new types like cobalt(3+/2+) complexes was not successful because of the poor compatibility between the ruthenium(II) sensitizer and the cobalt redox species. To address this problem and achieve higher power conversion efficiencies (PCEs), we introduce here six new cyclometalated ruthenium(II)-based dyes developed through ligand engineering. We tested DSCs employing these ruthenium(II) complexes and achieved PCEs of up to 9.4% using cobalt(3+/2+)-based electrolytes, which is the record efficiency to date featuring a ruthenium-based dye. In view of the complicated liquid DSC system, the disagreement found between different characterizations enlightens us about the importance of the sensitizer loading on TiO 2 , which is a subtle but equally important factor in the electronic properties of the sensitizers. ■ INTRODUCTIONThe global challenge to develop carbon-neutral renewable energy sources can be addressed by harnessing solar power using photovoltaics. 1 As an alternative to conventional solar cells, third-generation photovoltaic devices with dye-sensitized solar cells (DSCs) at the forefront have been extensively studied. 2 In standard DSCs, mesoporous TiO 2 is sensitized by a ruthenium(II) complex or an organic dye, and I 3 − /I − is widely employed as the most effective redox couple. 3,4 Congruence between the dye molecule chemisorbed on a mesoporous oxide and redox pair in the electrolyte in DSCs should be fine-tuned to obtain fast dye regeneration and ideally slow charge recombination. The present certified record power conversion efficiencies (PCEs) of up to 11.1% were achieved with I 3 − /I − and heteroleptic ruthenium dyes. 5−7 However, regeneration of a ruthenium(II) complex by electron donation from the I 3 − /I − redox couple entails a loss of around 500 mV, with over 300 mV of that being directly related to the complicated sequence of reactions associated with the two-electron oxidation of iodide that do not involve the sensitizer molecule. 8−10 The estimated lowest potential loss for the ruthenium metal complex/iodide system is around 750 mV, which limits the maximum obtainable conversion efficiency to 13.4%. 9,11 To boost the efficiencies further, redox couples with a smaller loss in potential were introduced. Among the one-electron redox pairs, 12,13 cobalt(3+/2+) is the most promising for the following two reasons: (i) DSCs with organic dyes and cobalt electrolytes are more stable in comparison to the cells with other one-electron shuttles; 14 (ii) it is possible to obtain cobalt complexes with various redox potentials just by ligand modification. 15,16 It is worth noting that the recent advances with copper(2+/1+) phenantroline-based electrolytes m...

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“…Triplet luminescence arises from either a metal‐to‐ligand charge‐transfer (MLCT) state or a ligand‐centered excited state 12–21. Emission wavelengths are subject to rational tuning 22–27. The complexes’ excited‐state properties make them light‐emitting beacons; their ground‐state attributes suggest them for experiments in cells 28–34…”

Section: Introductionmentioning

confidence: 99%

Cyclometalated Iridium(III) Complexes with Deoxyribose Substituents

Maity¹,

Choi²,

Teets³

et al. 2013

Chemistry A European J

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Fundamental study of enzymatic nucleoside transport suffers for lack of optical probes that can be tracked noninvasively. Nucleoside transporters are integral membrane glycoproteins that mediate the salvage of nucleosides and their passage across cell membranes. The substrate recognition site is the deoxyribose sugar, often with little distinction among nucleobases. Reported here are nucleoside analogues in which emissive, cyclometalated iridium(III) complexes are "clicked" to C-1 of deoxyribose in place of canonical nucleobases. The resulting complexes show visible luminescence at room temperature and 77 K with microsecond-length triplet lifetimes. A representative complex is crystallographically characterized. Transport and luminescence are demonstrated in cultured human carcinoma (KB3-1) cells.

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Extreme Tuning of Redox and Optical Properties of Cationic Cyclometalated Iridium(III) Isocyanide Complexes

Cited by 49 publications

References 65 publications

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

Ligand Engineering for the Efficient Dye-Sensitized Solar Cells with Ruthenium Sensitizers and Cobalt Electrolytes

Cyclometalated Iridium(III) Complexes with Deoxyribose Substituents

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