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Cationic cyclometallated iridium (iii) complexes
No full textOver the past two decades dramatic advances have been achieved in the field of organic electroluminescent devices, for display and lighting applications. A recent development in this field involves the use of ionic transition metal complexes (iTMCs) that have shown the possibility to fabricate single layer electroluminescent devices, named Organic Light-emitting Electrochemical Cells (OLECs) [1]. This type of device represents an interesting possible alternative to the more investigated organic light- emitting diodes (OLEDs). In OLECs, the charged complexes support all three processes of charge injection, charge transport and emissive recombination. Therefore, no additional layers are needed in the device and the emissive layer can be solution processed, which makes industrial manufacturing easier. At the moment, the most common cationic complexes are based on iridium, ruthenium, osmium, platinum, and copper [2]. Here we present a study on the use of three different cationic iridium(III) complexes [3,4] (Figure 1) in luminescent single layer devices in the presence and in the absence of an ionic liquid (IL).
The complex [Ir(ppy)2(5-CH3-1,10-phen)][PF6] (ppy = 2-phenylpyridine, phen = phenanthroline) reaches the most efficient results compared to the other ones. It has a very competitive brightness of 3040 cd/m2, obtained at 8V. The presence of IL lowers the turn-on time, and therefore, the operation voltage of the device at 3V. However, from the other side, the enhancement of the ions concentration into the film reduces the device lifetime t1/2, which is one of the main concern in light emitting devices.
1. J. Slinker, S. Bernhard, G. G. Malliaras et al., J. Mater. Chem., 17 (2007) 2976-2988.
2. L. De Cola, C. Bizzarri, M. Mydlak et al., Adv. Funct. Mater., 20 (2010) 1812–1820.
3. C. Dragonetti, D. Roberto, A. Valore et al., Inorg. Chem, 46 (2007) 8533-8547.
4. C. Dragonetti, D. Roberto, A. Valore et al., J.Phys. Chem. C, 113 (2009) 12517–12522
New diruthenium acetylide donor complexes for bulk-heterojunction solar cells
No full textConjugated polymers and oligomers have received a lot of attention as active materials for organic photovoltaic devices because of their potential for the development of plastic solar cells that are lightweight, flexible, and low cost. Bulk heterojunctions fabricated by blending polymers with fullerene derivative have resulted in great improvements in the polymer photovoltaic cell efficiencies.
The most commonly used materials are poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) [1], these cells with optimized device structure and fabbrication conditions can reach efficiencies in the range of 5-5.5%.
However, to produce highly efficient organic photovoltaic devices, it is necessary to extend the light absorption into the near-infrared region and at the same time preserve the high IPCE and open-circuit voltage.
Several papers have been recently dedicated to the investigation of the use of conjugated polymers incorporating heavy atoms; in particular Pt acetylide polymers as donors in solar cells using PCBM as acceptor [2] were proposed as a tool to enhance charge photogeneration. For instance, Mei et al. reported on a Pt acetylide-based polymer using a 2,1,3-benzothiadiazole (BTD) acceptor moiety flanked on either side by 2,5-thienyl (Th) donor units ([-Pt(L2)-t-Th-BTD-Th-t-]n, where L = PBu3), which absorbs strongly throughout the visible region. [3]
The use of Ru acetylides is a novel interesting tool for the design of donor materials [4] to combine with electron-withdrawing fullerides in bulk heterojunction solar cells.
New dinuclear Ru(II) complexes where two Ru atoms are separated by a bridge consisting of a 2,1,3 benzothiadiazole acceptor moiety flanked on either side by 2,5-thienyl or 3-hexyl substituted 2, 5 thienyl donor units were synthesized. (Figure 1)
These rather simple complexes appears to behave as a photoactive donor when blended with a fullerene as acceptor, thus being a first step toward novel bulk heterojunction solar cells, based on Ru donor systems
Figure 1
1. F. Padinger, R. S. Rittberger, N. S Sariciftci, Adv. Funct. Mater, 13 (2003) 85–88.
2. W.-Y. Wong, C.-L. Ho, Acc. Chem. Res. 43 (2010) 1246.
3. J.Mei, et al. Appl. Mater. Interfaces 1 (2009) 150.
4. A. Colombo, C. Dragonetti, D. Roberto, R. Ugo, L. Falciola, S. Luzzati, and D. Kotowski Organometallics (2011) doi: 10.1021om100846
Second-order nonlinear optical properties of cyclometallated Ir(III) and Pt(II) complexes
No full textThe second-order NLO properties of various cyclometallated cationic Ir(III) and neutral Pt(II) complexes were determined by both Electric Field Induced Second Harmonic generation (EFISH) and Harmonic Light Scattering (HLS) techniques.
Cationic 1,10-phenanthroline and bipyridine iridium(III) complexes (1, 2) are characterized by high negative EFISH β values which decrease when the ion-pair strength between the cation and the counterion (PF6–, C12H25SO3–) increases. Neutral Pt(II) complexes (3, 4) are also characterized by a good to high negative NLO response.
For all these cyclometallated complexes, the EFISH response is mainly controlled by MLCT/L'LCT processes. Interestingly, a combination of HLS and EFISH techniques, used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, shows that the major contribution is controlled by the octupolar part. [...]
1. V. Aubert, L. Ordronneau, M. Escadeillas, J. A. G. Williams, A. Boucekkine, E. Coulaud, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, A. Singh, J. Zyss, I. Ledoux-Rak, H. Le Bozec, V. Guerchais, Inorg. Chem. 2011. ASA
Second order non linear optical properties of neutral Ir(III) and Pt(II) complexes with substituted b-diketonate ligands.
No full textReproducible high-yield syntheses of [Ru3(CO)12], [H4Ru4(CO)12], and [Ru6C(CO)16]2− by a convenient two-step methodology involving controlled reduction in ethylene glycol of RuCl3·nH2O
No full textRu3CO12 [H4Ru4(CO)12], and [Ru6C(CO)16]2- have been synthesized in reproducible high yields and under mild conditions (1 atm) by a two-step methodology involving (i) first carbonylation of RuCl3·nH2O dissolved in ethylene glycol to give a mixture of tri- and di-carbonyl ruthenium(II) species, probably of the kind [Ru(CO)3Cl2(ethylene glycol)] and [Ru(CO)2Cl2(ethylene glycol)x ] (x = 1, 2), and (ii) addition of specific amounts of alkali carbonates and further reductive carbonylation to give the desired ruthenium carbonyl cluster. The selectivity of the second step is controlled by the: (i) nature and quantity of the alkali carbonate (Na2CO3 or K2CO3); (ii) gas-phase composition (CO or CO+H2); (iii) temperature
Simple novel cyclometallated iridium complexes for potential application in dye-sensitized solar cells
No full textDye-sensitized solar cells (DSSCs) are considered a real solution for harnessing the energy of the sun and converting it into electrical energy, exceeding the value of 11% efficiencies with the most performing Ru(II) sensitizers. The photosensitizer dye plays a key role in DSSCs, and iridium complexes are potentially good candidates for application in those kind of cells. Here we report the synthesis and characterization of three new simple cyclometallated Ir(III) complexes of the type: [Ir(C^N)2(4,4′- dicarboxybipyridine)][PF6] (C^N = variously substituted phenylpyridine cyclometallating ligand) and we try to understand if there is an influence of the nature of the cyclometallating ligand on the photovoltaic performance of the related dye-sensitized solar cells. The use of more conjugated π-delocalized cyclometallating ligands, that slightly shifts the UV bands to higher wavelengths, affords little better photovoltaic parameters. In addition we report the emission spectra and the emission quantum yields of all the phosphorescent Ir(III) complexes
Surface-mediated organometallic synthesis: high-yield syntheses of [Rh4(CO)12], [Rh6(CO)16], [Rh5(CO)15]− and [Rh12(CO)30]2− by controlled reduction of silica-supported RhCl3 or [Rh(CO)2Cl]2 in the presence of CH3CO2Na, Na2CO3 or K2CO3
No full textThe reductive carbonylation under 1 atm of CO of [Rh(CO)2Cl]2 supported on a silica surface added with a base such as CH3CO2Na, Na2CO3 or K2CO3, can be directed toward the formation of [Rh4(CO)12], [Rh6(CO)16] or K2[Rh12(CO)30] by controlling (i) the nature and amount of base; (ii) the amount of surface water; (iii) the reaction time; (iv) the temperature. Physisorbed [Rh6(CO)16] can also be prepared by direct controlled reductive carbonylation of RhCl3·nH2O supported on silica in the presence of well controlled amounts of CH3CO2Na. The neutral clusters [Rh4(CO)12] and [Rh6(CO)16] are easily recovered by extraction with dichloromethane whereas treatment of the generated silica-supported K2[Rh12(CO)30] with tetrahydrofuran affords K2[Rh12(CO)30] (by working under N2) or K[Rh5(CO)15] (by working under CO) in agreement with the easy conversion of these two clusters in solution. These efficient silica-mediated syntheses are comparable to conventional synthetic methods carried out in solution
Effect of the Coordination to the "Os3(CO)11" Cluster Core on the Quadratic Hyperpolarizability of trans-4-(4'-X-styryl)pyridines (X = NMe2, t-Bu, CF3) and trans,trans-4-(4'-NMe2-phenyl-1,3-butadienyl)pyridine
No full textCoordination to the “Os3(CO)11” cluster core of substituted styrylpyridines such as trans-4-(4’-NMe2-styryl)pyridine (L1), trans-4-(4’-t-Bu-styryl)pyridine (L2), trans-4-(4’-CF3-styryl)-pyridine (L3), or trans,trans-4-(4’-NMe2-phenyl-1,3-butadienyl)pyridine (L4) produces an enhancement of their quadratic hyperpolarizability, β EFISH, measured by the solution-phase dc electric-field-induced second harmonic (EFISH) generation method. This effect is due either
to a red-shift of the intraligand charge-transfer (ILCT) transition upon coordination (when the substituent in para position is a strong electron donor) or to a metal-to-ligand charge transfer (MLCT) transition (when the substituent is a strong electron acceptor). In the latter case the quadratic hyperpolarizability has a negative sign, due to the negative value of Δμeg. Therefore the “Os3(CO)11” cluster core displays an ambivalent acceptor or donor role. Some of the complexes investigated in this study show significant values (between 500x10-48 and 900x10-48 esu) of the product μβ0
Surface-mediated organometallic synthesis: the role of the oxidation state and of ancillary ligands in the high-yield and selective syntheses of platinum carbonyl dianions [Pt3(CO)6]n 2- (n = 6, 5, 4, 3) by reductive carbonylation under mild conditions and in the presence of surface basicity of various silica-supported Pt(IV) or Pt(II) compounds.
No full textThe reductive carbonylation under 1 atm of CO and in the presence of surface basicity of silica-supported Na-2[PtCl6], K-2[PtCl4], [Pt(CH3CN)(2)Cl-2], or [Pt(COD)Cl-2] (COD = cis,cis-1,5-cyclooctadiene) leads to the formation in high yields of platinum carbonyl dianionic clusters [Pt-3(CO)(6)](n)(2-) (n = 6, 5, 4, 3). Remarkably the silica surface plays a key role in these reductive carbonylations since no carbonyl cluster is obtained by reductive carbonylation of solid Na-2[PtCl6] in the absence of silica. The selectivity of the reaction can be easily tuned by controlling the surface metal loading, the basicity of the surface, and the nature of the platinum precursor (platinum oxidation state and nature of the coordination sphere). In particular, the one-step silica-mediated synthesis of [Pt-18(CO)(36)](2-) from K-2[PtCl4] (90% yield) is very convenient when compared to the traditional synthesis in methanol solution (67% yield), which requires two steps: (i) formation of [Pt-12(CO)(24)](2-) and (ii) addition of Na-2[PtCl6] drop by drop (molar ratio [Pt-12(CO)(24)](2-):Na-2[PtCl6] = 1:1) under a flow of CO
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