Modular synthesis of simple cycloruthenated complexes with state-of-the-art performance in p-type DSCs

A modular approach based on Suzuki-Miyaura cross coupling and Miyaura borylation has been used to prepare two cyclometallated [Ru(N^N)2(C^N)] + complexes which possess either a carboxylic or phosphonic acid group attached via a phenylene spacer to the 4-position of the pyridine ring in the C^N ligand. The key intermediate in the synthetic pathway is [Ru(bpy)2(1)] + where bpy = 2,2'-bipyridine and H1 is 4-chloro-2phenylpyridine. The crystal structure of [Ru(bpy)2(1)][PF6] is presented. Reaction of [Ru(bpy)2(1)][PF6] with 4carboxyphenylboronic acid leads to [Ru(bpy)2(H6)][PF6], while the phosphonic acid analogue is isolated as the zwitterion [Ru(bpy)2(H5)]. The cyclometallated complexes have been characterized by mass spectrometry, multinuclear NMR spectroscopy, absorption spectroscopy and electrochemistry. [Ru(bpy)2(5)] adsorbs onto NiO FTO/NiO electrodes (confirmed by solid-state absorption spectroscopy) and its performance in p-type dye-sensitized solar cells (DSCs) has been compared to that of the standard dye P1; two-screen printed layers of NiO give better DSC performances than one layer. Duplicate DSCs containing [Ru(bpy)2(H5)] achieve shortcircuit current densities (JSC) of 3.38 and 3.34 mA cm –2 and photoconversion efficiencies (η) of 0.116 and 0.109%, respectively, compared to values of JSC = 1.84 and 1.96 mA cm –2 and η = 0.057 and 0.051% for P1. Despite its simple dye structure, the performance of [Ru(bpy)2(H5)] parallels the best-performing cyclometallated ruthenium(II) dye in p-type DSCs reported previously (He et al, J. Phys. Chem. C, 2014, 118, 16518) and confirms the effectiveness of a phosphonic acid anchor in the dye and the attachment of the anchoring unit to the pyridine (rather than phenyl) ring of the cyclometallating ligand.


Introduction
There is growing interest in utilizing cyclometallated ruthenium(II) complexes as dyes in dye-sensitized solar cells (DSCs). 1,2,3Typical families of complexes are based upon [Ru(N^N) 2 (C^N)] + , [Ru(N^N^N)(C^N^N)] + and [Ru(N^N^N)(N^C^N)] + where archetype N^N, HC^N, N^N^N, HC^N^N and N^CH^N ligands are, respectively 2,2'-bipyridine (bpy), 2-phenylpyridine (Hppy), 2,2':6',2''-terpyridine (tpy), 6phenyl-2,2'-bipyridine and 1,3-bis(pyridin-2-yl)benzene.The majority of investigations have addressed dyes suited to electron injection at an n-type semiconductor interface, the driving force behind the use of anionic cyclometallating ligands being the replacement of thiocyanate ligands typically present in established Grätzel-type sensitizers.The panchromatic spectral response of [Ru(N^N) 2 (C^N)] + dyes in DSCs was identified by Grätzel in 2009. 4An advantage of incorporating cyclometallating domains in these complexes is the potential for HOMO-LUMO energy tuning by ligand functionalization, 5 and photoconversion efficiencies matching or exceeding that of the standard ruthenium dye N719 have been reported. 6he HOMO of a [Ru(N^N) 2 (C^N)] + complex is localized on the Ru/C^N unit. 7Therefore, in cyclometallated dyes for ntype DSCs, the C^N domain functions as an ancillary ligand and the N^N ligand (which contributes to the LUMO) carries the anchoring unit (e.g.carboxylic or phosphonic acid).The first oxidation process is typically shifted 900 mV less positive when compared with the relevant all-nitrogen donor analogue.By switching this functionalization pattern so that the anchor is positioned on the cyclometallating ligand, [Ru(N^N) 2 (C^N)] + and [Ru(N^N^N)(N^C^N)] + complexes become candidates for sensitizers in p-type DSCs (Fig. 1), or at the p-type interface in tandem cells. 8This potential has been proven, 9,10,11,12,13 efficiencies are generally low and the area remains ripe for further exploration.It has been demonstrated that tris(bpy)ruthenium(II)-or (bpy)tricarbonylchlororhenium(I)dyes bearing alkylphosphonate or phosphonic acid anchors bind to NiO, 14,15 but, to the best of our knowledge, [Ru(N^N) 2 (C^N)] + complexes with phosphonic acid anchoring

Experimental
General. 1 H, 13 C, 11 B and 31 P NMR spectra were recorded on a Bruker Avance III-400 or III-500 spectrometer at 295 K.The 1 H and 13 C chemical shifts were referenced with respect to residual solvent peaks (δTMS = 0), 11 B with respect to BF 3 .
Et 2 O, and 31 P with respect to 85% aqueous H 3 PO 4 .High resolution (HR) ESI-MS were measured on a Bruker maXis 4G instrument, and LC-ESI-MS using a combination of Shimadzu (LC) and Bruker AmaZon X instruments.An Agilent 8453 spectrophotometer was used to record absorption spectra.Solid-state absorption spectra of dye-functionalized electrodes were recorded using a Cary-5000 spectrophotometer.Microwave reactions were carried out in a Biotage Initiator 8 reactor.
Electrochemical measurements were made with a CHI 900B instrument using a glassy carbon working electrode, platinumwire auxiliary electrode, and silver-wire pseudo-reference electrode.Redox potentials were determined by both cyclic and square wave voltammetry.HPLC grade, argon-degassed DMSO or MeCN solutions (≈10 -4 mol dm -3 ) of samples were used in the presence of 0.1 M [ n Bu 4 N][PF 6 ] as supporting electrolyte; the scan rate was 0.1 V s -1 and ferrocene (Fc + /Fc) was the internal standard.

Crystallography
Single crystal data were collected on a Bruker APEX-II diffractometer; data reduction, solution and refinement used APEX2, SuperFlip and CRYSTALS respectively. 20,21,22tructure analysis used Mercury v. 3.6. 23,24Ru(bpy) 2 ( 1 Electrode preparation and device assembly.Each working electrode was prepared from an FTO glass plate (SolaronixTCO22-7, 2.2 mm thickness, sheet resistance ≈7 Ω square -1 ) which was cleaned by sonicating in Sonoswiss surfactant (2% in milliQ water), and rinsed with milliQ water and EtOH.The surface was activated in a UV-O 3 system (Model 256-220, Jelight Company Inc) for 20 min.Then the glass was immersed five times and air dried after every dipping in a [Ni(acac) 2 ] (ACROS) solution (MeCN 0.5 mM).The FTO plate was dried and a layer of NiO paste (Ni-Nanoxide N/SP, Solaronix) was screen printed (90T, Serilith AG, Switzerland).The printed plate was kept in an EtOH chamber for 3 min to reduce surface irregularities of the printed layer and dried for 6 min at 125 o C on a heating plate.Screen printing was used to give either one or two layers of NiO and then the electrodes were heated from room temperature to 350 °C over a period of 30 min, then kept at 350 °C for 30 min, then allowed to cool slowly to room temperature over ~2 h.After sintering, the FTO plate with the NiO screen printed dots was cut to make electrodes of size of 1 cm × 2 cm.After the final sintering, the thickness of a two-layer screen printed NiO surface was typically ~2.5±1.0 µm (by FIB measurements, recorded using a REM-FEI Helios NanoLab 650).The electrodes were heated at 250 o C for 20 min and then cooled to 80 o C before being immersed to a MeCN (0.3 mM) solution of P1 (Dyenamo AB) or [Ru(bpy) 2 ( 5)] (EtOH, 0.1 mM) for 20 h.The electrodes were removed from the solutions and were washed with EtOH and dried under a stream of N 2 .The fracture surfaces of electrodes screen printed with one or two layers of NiO were also examined by field-emission scanning electron microscopy (FE-SEM) using a Hitachi S-4800 equipped with a cold fieldemission electron source.
Commercial counter electrodes (Solaronix Test Cell Platinum Electrodes) were washed with EtOH and then heated on a hot plate at 450 o C for 30 min to remove volatile organic impurities.The DSCs were assembled by combining dye-covered FTO/NiO electrodes and Pt counter-electrodes using thermoplast hot-melt sealing foil (Solaronix, Meltonix 1170-25 Series, 60 µm thick) by heating while pressing them together.The electrolyte comprised I 2 (0.1 M), LiI (1 M) in MeCN.The electrolyte was introduced into the cell by vacuum backfilling.The hole on the counter electrode was finally sealed using the hot-melt sealing foil and a cover glass.Device performance measurements.The solar cell measurements were made using duplicate cells; the active area was 0.237 cm 2 .The DSCs were sun soaked from behind for 20 min at 1 sun irradiation and then measured immediately to obtain the current density-voltage (J-V) measurements with a LOT Quantum Design LS0811 instrument (100 mW cm -2 = 1 sun at AM1.5 and 23 o C).The instrument software was set to a p-type measurement mode (inverted configuration), with 360 ms as the settling time, and with a voltage step of 5.3 mV.The voltage was scanned from negative to positive values.

Synthesis and characterization of the [Ru(bpy) 2 (C^N)] + building block
Sensitizers for n-type DSCs incorporate a wide range of anchoring units. 25In order to establish a similar palette for ptype [Ru(bpy) 2 (C^N)] + dyes, we developed a modular strategy for synthesis based on Suzuki-Miyaura cross coupling and Miyaura borylation.The approach described below has the advantage that it can also easily be adapted to tune the electronic properties of the dye by replacing bpy by functionalized-bpy ligands in the cis-[Ru(bpy) 2 Cl 2 ] precursor.A Suzuki reaction between 2-bromo-4-chloropyridine and phenylboronic acid gave H1 in 64% yield.Compound H1 has previously been prepared by a Grignard reaction with 4chloropyridine-N-oxide in 74% yield, 17 but we find the Suzuki coupling more convenient.To widen the scope of our modular approach to {Ru(N^N) 2 (C^N)}-functionalization, we synthesized H2 using a Miyaura borylation (Scheme 2).The reaction was monitored by 1 H NMR spectroscopy and after ~5 hours, 40% conversion had been achieved.Attempts to increase the conversion using longer reaction times and higher ratios of catalyst, base or bis(pinacolato)diboron failed.The mixture of product and reagents were subjected to a Kugelrohr distillation and the residue was chromatographed.However, pure H2 could not be obtained.Further development of the synthetic strategy therefore utilized ligand H1.
The reaction of H1 with cis-[Ru(bpy) 2 Cl 2 ] in the presence of AgPF 6 (Scheme 3) following a procedure for [Ru(bpy) 2 (ppy)] + previously reported by one of us 26 gave [Ru(bpy) 2 ( 1)][PF 6 ] in 65.2% yield.The LC-ESI mass spectrum of the product exhibits a peak envelope at m/z 602.1 arising from the [M-PF 6 ] + ion.Fig. 2 and S1 † show the solution 1 H and 13 C NMR spectra, respectively, which were assigned using 2D methods (COSY, NOESY, HMQC and HMBC).The presence of the C^N chelate leads to inequivalent bpy ligands, as indicated by the ring labels in Scheme 3. A starting point for 1 H and 13 C NMR signal assignment is the lowest frequency signal at δ 6.46 ppm in the 1 H NMR spectrum (Fig. 2) which is characteristic of proton H F6 of the cyclometallated phenyl ring. 16 We recently commented on the paucity of structural data for [Ru(N^N) 2 (C^N)] + complexes. 16An updated search of the Cambridge Structural Database (CSD v. 5.37 with one update) using Conquest v. 1.18 revealed only 25 hits for discrete complexes containing a {Ru(bpy) 2 (ppy)}-core (Hppy = 2phenylpyridine; the bpy core-unit includes complexes with phen ligands).Single crystals of [Ru(bpy) 2 ( 1)][PF 6 ] were grown by vapour diffusion of Et 2 O into an MeCN solution of the complex.The compound crystallizes in the monoclinic space group P2 1 /n with both the Λ-and Δ-[Ru(bpy) 2 (1)] + cations present in the unit cell.Fig. 3 shows the structure of the Λ-[Ru(bpy) 2 (1)] + cation and selected bond distances and angles are given in the figure caption.The structure exhibits no surprises, being similar to that of the analogous complex in which the chloro substituent in coordinated [1] -is replaced by a methyl acetate group. 16As in the latter structure, efficient faceto-face and edge-to-face π-contacts between enantiomers is observed (Fig. 4).For the face-to-face interaction, the distance

Synthesis and characterization of anchoring unit building blocks
We decided to target [Ru(bpy) 2 (C^N)] + dyes with CO 2 H or P(O)(OH) 2 anchoring groups, and therefore required anchoring modules capable of undergoing Suzuki-Miyaura cross coupling with [Ru(bpy) 2 (1)] + .For the carboxylic acid anchor, a suitable reagent is a commercially available 4-carboxyphenylboronic acid.The phosphonic acid anchoring module was synthesized by the route shown in Scheme 4. Diethyl 4bromobenzenephosphonate (Scheme 4) has previously been prepared in 22% from 1,4-dibromobenzene by Grignard reaction. 18We were able to isolate the phosphonate ester in 73% yield by a palladium-catalysed phosphonation of 1-bromo-4-iodobenzene (selective at the iodo-functionality) using a stoichiometric amount of HPO(OEt) 2 .Further functionalization by Miyaura borylation using bis(pinacolato)diboron yielded the diester 3 (Scheme 4); this was used in the next step without purification.Compound 3 was recently reported as part of a wide-ranging study of regioselective aromatic C-H borylations, 19 and the 1 H NMR spectroscopic data agreed with those published.In the 31   The final step of the synthesis of cyclometallated ruthenium complexes functionalized with anchoring groups is a cross coupling of [Ru(bpy) 2 (1)] + with 4-carboxyphenylboronic acid or H 2 4 (Scheme 5).Table 1 summarizes the reaction conditions investigated during optimization; reactions were monitored using LC-ESI-MS.Initial attempts to couple [Ru(bpy) 2 (1)] + with 4-carboxyphenylboronic acid using typical Suzuki coupling conditions with catalytic amounts of Pd(OAc)2 did not give the desired product.Although [Ru(bpy) 2 (1)] + was consumed, LC-ESI-MS confirmed that the products were [Ru(bpy)2(ppy)] + (resulting from palladium-catalysed dehalogenation) and the homocoupled product [(bpy)2Ru(µdppy)Ru(bpy) 2 ] + (dppy = 2,2'-diphenyl-4,4'-bipyridine).To overcome this problem, we turned to a catalyst containing the sterically demanding SPhos ligand which has been shown by O'Connor 27 to be effective for the Suzuki coupling of 4carboxyphenylboronic acid with an aryl chloride.The second generation precatalyst SPhos Pd G2 does not require reducing agents for activation and is highly reactive.Under microwave conditions (Table 1), Suzuki-Miyaura coupling of [Ru(bpy) 2 (1)] + with 4-carboxyphenylboronic acid using SPhos Pd G2 in EtOH solvent showed a 91% selectivity for the desired product and no homocoupling was observed.However, if similar conditions are used for the reaction between [Ru(bpy) 2 (1)] + and H 2 4, only 31% selectivity was achieved (Table 1).The choice of solvent is known to influence the dehalogenation reaction, 28 and therefore EtOH was replaced by a 1:1 mixture of MeCN and H 2 O.This choice was made, in part, for solubility reasons.Under the conditions shown in Table 1, the Suzuki-Miyaura cross coupling of [Ru(bpy) 2 (1)] + and 4-carboxyphenylboronic acid proceeded with both 100% conversion and selectivity.For the reaction with anchoring module H 2 4, the highest selectivity achieved was 97%; adjustments to the temperature and time (Table 1) were required for optimization of selectivity.

Conversion of [Ru(bpy) 2 (1)] + to potential sensitizers
The electrospray mass spectra of the products revealed peak envelopes at m/z 724.2 and 688.1, respectively.However, on their own, these results are ambiguous, because they are consistent with either [M+H] + for M being a zwitterion [Ru(bpy) 2 (H5)] or [Ru(bpy) 2 (6)], or [M-PF 6 ] -for salts [Ru(bpy) 2 (H 2 5)][PF 6 ] and [Ru(bpy) 2 (H6)][PF 6 ].Elemental analysis for the phosphonic acid-functionalized compound was consistent with the zwitterion shown in Scheme 5, and this was further supported by the response of the 31 P NMR spectrum to the addition of base or acid.Fig. 5 shows that the signal at δ +10.8 ppm that characterizes the isolated complex shifts to δ +15.2 ppm after TFA vapour has been blown over the mouth of the NMR tube.Addition of a little solid K 2 CO 3 to the same NMR sample results in a shift back to lower frequency (δ +10.6 ppm with a shoulder at δ +10.7 ppm).A resonance at approximately the same frequency results if K 2 CO 3 is added to a solution of the isolated complex.These observations indicate that the complex is the zwitterion [Ru(bpy) 2 (H5)].In contrast, the second product is formulated as [Ru(bpy) 2 (H6)][PF 6 ]; the 31 P NMR spectrum showed a septet at δ -144.7 ppm (J PF = 727 Hz) characteristic of the hexafluoridophosphate anion.The difference in protonation states in the isolated ruthenium complexes is consistent with the pK a values of structurally related pairs of carboxylic and phosphonic acids, e.g. for PhCO 2 H, pK a = 4.20 and for PhPO 3 H 2 , pK a (1) = 1.86. 29ble 1.Conditions and product selectivity for Suzuki-Miyaura cross coupling of [Ru(bpy)2(1)] + with 4-carboxyphenylboronic acid or H24.The complexes [Ru(bpy) 2 (H5)] and [Ru(bpy) 2 (H6)][PF 6 ] were characterized by 1 H and 13 C NMR spectroscopies, the spectra being assigned using COSY, HMQC and HMBC methods.The 1 H NMR spectra are shown in Fig. S2 †.We noted that when an acetone-d 6 solution of [Ru(bpy) 2 (H6)][PF 6 ] was left to stand for several days, the 1 H NMR signals for protons H G2 and H G3 (the ring to which the CO 2 H group is attached) broadened and shifted (Fig. S3 †); some precipitate was also observed in the NMR tube.We attribute this to a change in protonation state, but have not investigated the system in detail.

DSC working-electrode fabrication
The fabrication of FTO/NiO photocathodes in p-type DSCs is a critical part of the device fabrication. 32,33Initially, 34 we investigated doctor blading and screen-printing the FTO glass with different numbers of layers of NiO, combined with pretreatment of the FTO glass with dip-coated or spin-coated [Ni(OAc) 2 ] or [Ni(acac) 2 ] to improve adhesion of the NiO paste. 35,36The surface morphology of the electrodes was investigated using SEM and FIB imaging (see Experimental section).Pretreating the FTO glass with [Ni(acac) 2 ] followed by two screen-printed layers of NiO paste lead (after sintering involving a cycle between room temperature and 350 °C, see Experimental section) to a NiO layer thickness of ~2.5±1.0 µm (Fig. 7).This is typical of NiO photocathodes used in p-type DSC studies 37,38 and is compatible with the limitation imposed by the diffusion length of a hole in the NiO semiconductor. 38A recent investigation using the standard P1 dye (Scheme 6) 33 confirms that two-layers of screen-printed commercial (Dyenamo) NiO lead to better performing p-type DSCs than using one layer.

DSC performances
The p-type DSCs were assembled as described in the Experimental Section, and duplicate DSCs were made for each dye.Previous investigations of cyclometallated ruthenium(II) dyes have employed an electrolyte comprising I -/I 3 -/MeCN (with no additives), 9,10,11,13 a composition regularly used for the standard dye P1.For DSC measurements, a settling time of 360 ms gave reproducible J-V curves whether the voltage was scanned from negative to positive, or from positive to negative, potentials.Settling times of ≤200 ms led to J-V curves that differed with the direction of the scan; a settling time of 360 ms was therefore adopted as standard for all measurements.
Before discussing the results, we draw attention to the fact that literature photoconversion efficiencies (η) of standard dye P1 in p-type DSCs show significant variation. 33,39,40ontributing factors include the method of NiO fabrication and layer thickness, 32,33 and the electrolyte (MeCN/I 2 /LiI, MeCN/I 2 /LiI/TBP, or LiI/I 2 /propylene carbonate). 41,42,43,44,45,46he use of MeCN in place of propylene carbonate in the electrolyte is beneficial in terms of short-circuit current density (J SC ).It is also important to note that for n-type DSCs, the use of different sun simulators (e.g.Solaronix vs LOT) also leads to differing J SC values. 47In a bench-marking investigation, 33 Gibson and coworkers included measurements of the performance of p-type DCSs with P1 with a variety of different fabrication methods.The study included electrodes with one screen-printed layer of Solaronix NiO paste and a sintering temperature of 350 o C, leading to values of J SC = 1.57mA cm -2 , open-circuit voltage (V OC ) = 93 mV, fill-factor (ff) = 32%, and η = 0.047%.We have fabricated DSCs that are directly comparable to the latter except for the inclusion of the Ni(acac) 2 pretreatment (see above) which we find essential for good adhesion of the NiO to the FTO glass.The performance data for P1 (Table 3, one-layer of NiO) are similar to those reported, 33 validating the data presented below.We find an enhanced DSC performance for P1 is obtained by using twolayers of NiO (Table 3).
Table 3 also gives values of J SC , V OC , ff and η for DSCs sensitized with the cyclometallated dye [Ru(bpy) 2 (H5)] with electrodes made with one or two screen-printed layers of NiO.As for P1, better DSC performances are observed for twolayers of NiO.J-V curves for the DSCs containing [Ru(bpy) 2 (H5)] adsorbed on two-layers of NiO are shown in Fig. 9.The low fill-factors of p-type DSCs are a known phenomenon. 48Pairs of DSCs (Table 3 and Fig. 9) give reproducible DSC parameters.Pleasingly, J SC values and η are significantly better for [Ru(bpy) 2 (H5)] than for P1, and both J SC and η are comparable with the best values (J SC = 3.43 mA cm -2 and η = 0.109% for the dye shown in Scheme 7) 9 reported for cyclometallated ruthenium dyes 9,10,11,13 or for two recently reported diacetylide ruthenium(II) donor-π-acceptor dyes (J SC = 1.50 and 2.25 mA cm -2 , η = 0.038 and 0.079%). 49Values of V OC = 93 mV and ff = 33% for the dye in Scheme 7 compare favourably with the observed values of V OC and ff (Table 3) for [Ru(bpy) 2 (H5)].Given that [Ru(bpy) 2 (H5)] is a model dye, its promising performance suggests that the phosphonic anchor is beneficial.Furthermore, while DFT calculations indicate that the anchoring unit is most beneficially attached to the cyclometallating ring which contributes significantly to the HOMO of a [Ru(N^N) 2 (C^N)] + complex, 11 [Ru(bpy) 2 (H5)] achieves a value of J SC =3.38 mA cm -2 with the anchoring unit in the 4-position of the pyridine ring of the C^N ligand.Scheme 7. Structure of a cyclometallated ruthenium dye that achieves JSC = 3.43 mA cm -2 and η = 0.104%.9

Conclusions
We have described a readily adaptable modular strategy for cyclometallated ruthenium(II) complexes [Ru(bpy) 2 (H6)][PF 6 ] and [Ru(bpy) 2 (H5)] which possess a carboxylic or phosphonic acid group attached via a phenylene spacer to the 4-position of the pyridine ring in the cyclometalling ligand.The isolation of the the zwitterion [Ru(bpy) 2 (H5)] versus the cationic [Ru(bpy) 2 (H6)] + is consistent with the difference between the pK a values of RPO 3 H 2 and RCO 2 H.The key intermediate in the synthetic pathway is the chloro-derivative [Ru(bpy) 2 (1)] + which has been structurally characterized as the [PF 6 ] -salt.
[Ru(bpy) 2 (H5)] has been evaluated as a dye in p-type DSCs and its performance compared to that of the standard dye P1; DSC parameters for the latter were first validated against the benchmarking work of Gibson and coworkers. 33Duplicate DSCs containing [Ru(bpy) 2 (H5)] exhibit values of J SC = 3.34 and 3.38 mA cm -2 and η = 0.116 and 0.109% making this structurally simple dye comparable to the best-performing cyclometallated ruthenium(II) dye in p-type DSCs previously reported. 11[Ru(bpy) 2 (H5)] achieves values of V OC = 95 mV and ff = 34-36%.The performance parameters confirm the effectiveness of a phosphonic acid anchor in the dye and the attachment of the anchoring unit to the pyridine ring of the cyclometallating ligand.We are currently investigating the improvement of the performance of this and related ruthenium(II) dyes in p-type DSCs, and are striving to understand the factors that contribute to the surprisingly good performance of the structurally simple [Ru(bpy) 2 (H5)].

Fig. 1 .Scheme 1 .
Fig. 1.Working principle of a p-type DSC.S and S* are the ground and excited states of the dye; EVB represents the quasi-Fermi level of the valence band of the semiconductor; VOC = open circuit voltage.

Fig. 7 .Scheme 6 .
Fig. 7. FIB images of an FTO/NiO electrode with [Ni(acac)2] pretreatment and two screen-printed layers of NiO sintered at 350 °C: (a) top surface, and (b) a gallium beam cut into the NiO with a platinum layer is deposited on top of the NiO surface.In (b), the glass and FTO coating are visible beneath the NiO.

CN
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Cl 2 (75 ml) was heated at reflux for 19 h.The reaction mixture was filtered over celite and washed thoroughly with CH 2 Cl 2 .The solvent was removed under vacuum and the dark purple residue was purified by column chromatography (alumina, acetone/pentane 2:1, changing to acetone).After solvent evaporation, an oil was isolated.The oil was diluted with CH 2 Cl 2 and then hexanes were added to precipitate the product.After filtration, [Ru(bpy) 2 (1)][PF 6 ] was isolated as a
11 1 H} NMR spectrum, 3 is characterized by a signal at δ +18.6 ppm, and in the11B NMR spectrum by a resonance at δ +22.4 ppm.Deprotection of 3 to give acid H 2 4 was achieved with Me 3 SiBr.Whereas the diester 3 is readily soluble in CH 2 Cl 2 and CHCl 3 , acid H 2 4 is soluble only in solvents such as DMSO; in DMSO-d 6 , H 2 4 exhibits signals in the 31 P{ 1 H} and 11 B NMR spectra at δ +12.2 and +28.4 ppm, respectively.In the LC-ESI mass spectrum of H 2 4, a peak at m/z = 285.1 was assigned to [M+H] + .

Table 3 .
Performance data for duplicate DSCs containing dyes [Ru(bpy)2(5)] or P1.Measurements were made on the day of sealing the DSCs.