Coumarin-substituted manganese phthalocyanines: synthesis, characterization, photovoltaic behaviour, spectral and electrochemical properties

DaltonTransactions

PAPER

Cite this: Dalton Trans., 2014, 43,7987

Received 14th February 2014,Accepted 17th March 2014

DOI: 10.1039/c4dt00482e

www.rsc.org/dalton

Coumarin-substituted manganesephthalocyanines: synthesis, characterization,photovoltaic behaviour, spectral andelectrochemical properties

Selçuk Altun,a Zafer Odabaş,*a Ahmet Altındalb and Ali Rıza Özkaya*a

The synthesis and spectroscopic characterization of novel manganese(III) phthalocyanines bearing 7-oxy-

4-(4-methoxyphenyl)-8-methylcoumarin or/and chloro groups have been achieved. The effect of alpha

and beta substitution on the ligand- and metal-based reduction processes of the manganese phthalo-

cyanine complexes and their interaction with dioxygen were investigated. The more effective interaction

of the central metal of the beta coumarin substituted complex with dioxygen than that of its alpha substi-

tuted analogue was attributed to the hindrance of the interaction by the nonplanarity in the case of alpha

substitution. Similarly, the aggregation tendency was lower in the case of alpha substitution. Among the

fabricated coumarin-substituted manganese phthalocyanine donor layer and fullerene (C60) acceptor

based photovoltaic heterojunction devices, the one containing 8 exhibited the best performance. The

effect of the thickness of the active Pc layer on solar cell parameters has also been investigated. A nearly

thickness independent open circuit voltage was observed.

1. Introduction

Phthalocyanines (Pcs) are typically blue or green macrocycliccompounds similar in structure to tetraazaporphyrins, buthaving four additional fused benzo rings.1,2 Pcs have planarand 18 π-electron heterocyclic aromatic systems.2 A greatnumber of unique properties of these compounds arise fromthis electronic delocalization that makes these compoundsvaluable in different fields of technology. Their classical use asdyes3 is now overshadowed by other applications such assensors, photodynamic therapy of cancer, optical recording,nonlinear optical materials, electronic device components,photovoltaics, catalysts and electrochromism.4–7 Recently, red-coloured manganese Pcs for analogs, substituted with highlyhindered, bulky hexadecaalkoxyl functional groups, have beenreported,8 as well as other red Pcs bearing alkylthio9 andphenyl10 groups have been described. These analogs representPcs exhibiting pronounced red shifts. Previously, some highlyred-shifted analogs of some Pcs had been prepared with somedifficulty owing to insolubility11 and decomposition pro-

blems.12 Highly red-shifted analogs of Pcs, having additionalbenzo groups attached to the Pc benzo groups such asnaphthalocyanines and anthracocyanines,13 are usuallydifficult to prepare, highly insoluble, and prone todecomposition.12

Coumarin (2H-1-benzopyran-2-one, 2H-chromen-2-one)derivatives are biologically active compounds with numerousmetabolites and are widespread in nature.14 These compoundsare one kind of significant organic fluorescent chromophoresand widely used in some applications such as for synthesizinglaser dyes, chemo sensors for metal detection, pH sensors,liquid crystals and organic non-linear optical materials, due totheir characteristics of high emission yield, excellent photo-stability and extended spectral range.15 In view of the versatileimportance of both coumarins and MnPcs it is worthwhile tocombine these two functional groups into a single hybrid com-pound via a synthetic methodology and characterize its deriva-tives, which may also exhibit high solubility in various solventsand intriguing physicochemical properties.

Both the central metal- and conjugated 18 π-electronligand-based rich redox properties of Co(II), Fe(II), Mn(II) andMn(III)Pcs with variable oxidation states ranging from M(I) toM(IV) usually make these compounds valuable16–18 comparedto other first row transition MPcs since their applications invarious areas such as sensors, catalysts and electrochromicmaterials are closely related to their electrochemical pro-perties.12,18,19 However, the studies on the electrochemistry of

aDepartment of Chemistry, Marmara University, 34722 Göztepe-Istanbul, Turkey.

E-mail: [email protected], [email protected],

[email protected]; Fax: +90 216 3478783; Tel: +90 216 3479641bDepartment of Physics, Yildiz Technical University, Davutpasa Caddesi, 34220

Esenler, Istanbul, Turkey. E-mail: [email protected]; Fax: +90 212 383 42 34;

Tel: +90 212 383 42 31

This journal is © The Royal Society of Chemistry 2014 Dalton Trans., 2014, 43, 7987–7997 | 7987

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MnPcX complexes are still scarce and therefore, their electro-chemistry is not accurately defined, in comparison with otherfirst row transition MPcs.12,18,20 For instance, the firstreduction process of Mn(III)Pc(−2)X− may be followed by[Mn(II)Pc(−2)X−]−/[Mn(II)Pc(−3)X−]2

− or [Mn(II)Pc(−2)X−]−/[Mn(I)Pc(−2)X−]2

− processes. These processes are also expectedto be associated by coordination–noncoordination equilibriumof X−. Furthermore, the reduction processes of manganese Pcsare very sensitive to the presence of oxygen and thus, may becomplicated by the formation of μ-oxo MnPc species.

Development of devices for conversion of solar energy intoelectricity has attracted great attention in recent years due tostrong interest in renewable energy and the problem of globalclimate changes. Solar cells based on organic semiconductingmaterials have the potential to compete with more maturecrystalline and thin film based Si photovoltaic technologies inthe future, primarily due to the significantly reduced manufac-turing costs and facile processing.21 Therefore, a great efforthas been focused since last few years on development of lowcost solar cells. The Pc compounds are indispensable com-ponents as the donor for the high efficiency bulk-heterojunc-tion organic photovoltaic devices.22 Besides high stability andeffective hole transport, these materials offer a high architec-tural flexibility in the structure, which facilitates the tailoringof their physical, optoelectronic and chemical parameters overa very broad range.

In this study, alpha tetra, beta tetra, beta octa coumarinand beta octa coumarin–chlorine substituted Mn(III)Pcs havebeen synthesized from 4-(4-methoxyphenyl)-8-methylcou-marin-7-oxy substituted phthalonitrile derivatives (Scheme 1).The characterization of the compounds was achieved byelemental analyses, UV-vis, IR and matrix assisted laser deso-rption/ionization-time of flight (MALDI-TOF) mass spec-troscopy. The electronic absorption properties of newlysynthesized compounds were investigated in different solventssuch as toluene, dichloromethane (DCM), tetrahydrofuran(THF) and dimethylsulfoxide (DMSO). The redox properties ofthe complexes were determined not only by electrochemicalbut also by in situ spectroelectrochemical measurements. The

photovoltaic properties of these coumarin-substituted manga-nese Pcs were also studied.

2. Experimental section2.1. Materials and methods

IR spectra and electronic spectra were recorded on a ShimadzuFTIR-8300 (KBr pellet) and a Shimadzu UV-1601 spectrophoto-meter, respectively. Elemental analyses were performed by theInstrumental Analysis Laboratory of TUBITAK, Ankara. Massspectra were acquired on a Autoflex III MALDI-TOF massspectrometer (Bruker Daltonics, Germany) equipped with anitrogen UV-laser operating at 337 nm in the reflectron modewith an average of 50 shots.

2.2. Sample and matrix preparation

The compound, α-cyano-4-hydroxycinnamic acid (ACCA), wasprepared in THF at a concentration of 10 mg mL−1 as a matrix.MALDI samples were prepared by mixing sample solutions(2 mg mL−1 in chloroform) and matrix solution (1 : 10 v/v) in a0.5 mL Eppendorf® microtube. Finally, 0.5 μL of this mixturewas deposited on the sample plate, dried at room temperature,and then analyzed.

2.3. Synthesis

2.3.1. General procedure for synthesis of manganese(III)Pcs(5–8). A mixture of phthalonitrile compounds (1, 2, 3 or 4)(approximately 0.20 g, 4.50 × 10−4 mol), MnCl2·4H2O (0.10 g,5 × 10−4 mol) and 0.30 mL of dimethylformamide (DMF) washeated in a sealed glass tube for 20 minutes under a dry N2

atmosphere at 320 °C. After cooling to room temperature,3 mL of DMF was added to the residue to dissolve the product.The reaction mixture was precipitated with methanol. The pre-cipitate was filtered and washed with hot water, methanol andacetonitrile for 12 hours in the Soxhlet apparatus, respectively.The crude product was purified by column chromatographywith silica gel eluting with chloroform a gradient of chloro-form–THF from 0 to 5% THF.

2.3.1.1. Synthesis of 1(4),8(11),15(18),22(25)-tetra(4-(4-meth-oxyphenyl)-8-methylcoumarin-7-yloxy)manganese(III)phthalocyanine(5). Compound 5 was obtained and purified by the generalprocedure as explained above. MnPc 5 is soluble in toluene,DCM, chloroform, THF, DMF and DMSO. Mp > 350 °C. Yield:80.0 mg (36.36%). Anal calculated for C100H64MnN8O16Cl:C 69.67%, H 3.74%, and N 6.50%, obtained results: C 69.49%,H 3.93%, N 6.68%. IR (KBr pellet) νmax/cm

−1: 527, 563, 603,743, 834, 865, 896, 958, 1022, 1084, 1172, 1242, 1327, 1366,1420, 1482, 1484, 1510, 1580, 1603, 1718, 2842, 2932, 3073.MALDI-TOF-MS: m/z 1642.590 (M − Cl − 3CH3)

+, 1657.609(M − Cl − 2CH3)

+, 1672.657 (M − Cl − CH3)+, 1687.794

(M − Cl)+, 1710.721 (M − Cl + Na)+ and 1726.614 (M − Cl + K)+.UV-vis(DCM): λmax(nm), (log ε): 288 (5.981), 531 (5.246),676 (5.369), 752 (6.025).

2.3.1.2. Synthesis of 2(3),9(10),16(17),23(24)-tetra(4-(4-meth-oxyphenyl)-8-methylcoumarin-7-yloxy)manganese(III)phthalocyanine

Scheme 1 Synthesis of 5–8. Reagents and conditions: i: MnCl2·4H2O,dimethylformamide, N2, 320 °C, 20 min.

Paper Dalton Transactions

7988 | Dalton Trans., 2014, 43, 7987–7997 This journal is © The Royal Society of Chemistry 2014

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(6). Compound 6 was obtained and purified by the generalprocedure as explained above. MnPc 6 is soluble in toluene,DCM, chloroform, THF, DMF and DMSO. Mp > 350 °C. Yield:145.0 mg (69.90%). Anal calculated for C100H64MnN8O16Cl:C 69.67%, H 3.74%, and N 6.50%, obtained results: C 69.85%,H 3.50%, N 6.67%. IR (KBr pellet) νmax/cm

−1: 529, 563, 603,617, 662, 743, 811, 831, 865, 884, 955, 1000, 1025, 1078, 1175,1242, 1293, 1332, 1363, 1394, 1437, 1484, 1510, 1594, 1721,2836, 2932, 3068. MALDI-TOF-MS m/z 1672.705 (M − Cl −CH3)

+, 1687.616 (M − Cl)+, 1710.520 (M − Cl + Na)+ and1726.417 (M − Cl + K)+. UV-vis(DCM): λmax(nm), (log ε): 292(6.052), 520 (5.476), 667 (5.401), 730 (5.940).

2.3.1.3. Synthesis of 2,9,16,23-tetra(chloro)-3,10,17,24-tetra-(4-(4-methoxyphenyl)-8-methyl-coumarin-7-yloxy)manganese(III)-phthalocyanine (7). Compound 7 was obtained and purified bythe general procedure as explained above. MnPc 7 is soluble intoluene, DCM, chloroform, THF, DMF and DMSO. Mp >350 °C. Yield: 77.0 mg (31.81%). Anal calculated forC100H60Cl4MnN8O16Cl: C 63.81%, H 3.21%, and N 5.95%,obtained results: C 63.99%, H 3.05%, N 6.06%. IR (KBr pellet)νmax/cm

−1: 529, 563, 614, 659, 743, 760, 811, 833, 865, 887,954, 1000, 1022, 1070, 1171, 1242, 1290, 1332, 1366, 1437,1506, 1591, 1728, 2836, 2920, 3058. MALDI-TOF-MS: m/z1808.352 (M − Cl − CH3)

+, 1823.352 (M − Cl)+, 1846.458 (M −Cl + Na)+. UV-vis(DCM): λmax(nm), (log ε): 291 (5.997), 519(5.182), 663 (5.365), 728 (5.932).

2.3.1.4. Synthesis of 2,3,9,10,16,17,23,24-octa(4-(4-methoxy-phenyl)-8-methyl-coumarin-7-yloxy)manganese(III)phthalocyanine(8). Compound 8 was obtained and purified by the generalprocedure as explained above. MnPc 8 is soluble in toluene,DCM, chloroform, THF, DMF and DMSO. Mp > 350 °C. Yield:23.0 mg (10.45%). Anal calculated for C168H112MnN8O32Cl:C 70.42%, H 3.94%, and N 3.91%, obtained results: C 70.59%,H 3.87%, N 4.10%. IR (KBr pellet) νmax/cm

−1: 526, 554, 734,833, 864, 881, 924, 955, 1025, 1087, 1141, 1158, 1175, 1247,1262, 1332, 1366, 1387, 1431, 1470, 1571, 1605, 1721, 2864,2920, 2954, 3056. MALDI-TOF-MS: m/z 2762.545 (M − Cl −3CH3)

+, 2777.569 (M − Cl − 2CH3)+, 2792.611 (M − Cl − CH3)

+,2807.762 (M − Cl)+, 2830.601 (M − Cl + Na)+, 2853.689 (M −Cl + 2Na)+ and 2876.625 (M − Cl + 3Na)+. UV-vis(DCM):λmax(nm), (log ε): 299 (6.409), 499 (5.018), 653 (5.453), 726(5.975).

2.4. Electrochemical and in situ spectroelectrochemicalmeasurements

A PAR VersoStat II Model potentiostat/galvanostat controlledby an external PC and combined with a three-electrode con-figuration was employed for cyclic voltammetry measurementsat 25 °C. The reference, the counter and the working electrodeswere a Saturated Calomel Electrode (SCE) separated from thebulk of the solution by a double bridge, a Pt wire and a Ptplate with a surface area of 0.10 cm2, respectively. The support-ing electrolyte at a concentration of 0.10 mol dm−3 was electro-chemical grade tetrabutylammonium perchlorate (TBAP) inextra pure DMSO. An Agilent Model 8453 diode array spectro-photometer and an optically transparent thin layer cell

(OTTLC) with the three-electrode configuration were equippedwith the potentiostat/galvanostat to carry out in situ spectro-electrochemical measurements at 25 °C. A transparent Ptgauze, a SCE separated from the bulk of the solution by adouble bridge and a Pt wire were used as the working, thereference and the counter electrodes, respectively.

2.5. Photovoltaic device preparation and measurements

The devices were fabricated on patterned indium tin oxide(ITO) coated glass substrates with a sheet resistance of 15–20Ω cm−2. The ITO coated substrates were cleaned by ultrasonictreatment in acetone, isopropyl alcohol, and deionized water.After routine solvent cleaning, the substrates were exposed toUV ozone for 20 min immediately prior to coating organiclayers. The organic materials used in the fabrication of solarcells were 5–8 and C60. These compounds were used withoutany purification, as donor and acceptor, respectively. The thinfilms of the Pcs with different thickness values between 30and 110 nm were deposited on the patterned indium-tin oxide(ITO) substrate by a spin coating method using chloroform asthe solvent. Subsequently, the films were thermally annealedat 120 °C for 20 min to evaporate the solvent. Then, on the topof the Pc layer, C60 with the thickness of 30 nm was grownsequentially by vacuum thermal evaporation at a pressurebelow 10−5 mbar. The thickness of the acceptor layer was fixedat 30 nm. Finally, a 400 nm thick Al cathode was evaporatedthrough a shadow mask to define several devices with theactive area of approximately 0.15 cm2. During evaporation,there was no vacuum break between organic (C60) and metal(Al) deposition. An elipsometric technique was used tomeasure the thickness of the films. The electrical transport inthe devices was studied via current–voltage (I–V) characteristicsusing a Keithley 617 electrometer. All the electrical measure-ments were performed in ambient air at room temperature.We have investigated the change in solar cell performance,including short circuit current density ( Jsc), open circuitvoltage (Voc), photovoltaic conversion efficiency (η), and fillfactor (FF), as a function of Pc layer thickness under AM1.5illumination (100 mW cm−2).

3. Results and discussion3.1. Synthesis and characterization

The starting materials, phthalonitrile derivatives (1–4), havebeen synthesized by the method in the literature.18,19,23

Manganese(III)Pcs (5, 6, 7 and 8) bearing (4-methoxyphenyl)-8-methylcoumarin-7-oxy and/or chloro substituents, obtained inmoderate yields (36% for 5, 70% for 6, 32% for 7, and 10% for8), were purified and characterized to investigate differences intheir spectroscopic and aggregation behaviours. The character-ization of the new products involved a combination ofmethods including IR, UV-vis, and MALDI-TOF mass spec-trometry and elemental analyses. The results are consistentwith the proposed structures. 1H-NMR measurement of theMnPcs was precluded owing to their paramagnetic nature.

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The FT-IR spectra of Pcs 5–8 showed Ar–O–Ar, –CvC–,–CvO, –CH3 and aromatic –CH– peaks in the ranges of1242–1247, 1591–1605, 1718–1728, 2836–2932 and3056–3073 cm−1, respectively. In addition, the absence of–CuN peaks in the range of 2229–2235 cm−1 in the spectraclearly indicated that starting compounds 1–4 were convertedto the Pcs 5–8.

Since Mn(II)chloride·4H2O was used in the synthesis of thecomplexes, the formation of Mn(II)Pc products was expected.However, the Q-band absorption in the UV-vis spectra of theproducts is considerably red-shifted. This observationsuggested the formation of Mn(III)PcX-type complexes. Theaerobic conditions in purification processes were probably themain reason for the formation of Mn(III)PcX products.24 Aspurification takes place under aerobic conditions, it can beexpected that the Mn(III)Pc species is formed. The UV-visspectra of Pcs 5–8 in various solvents (toluene, DCM, THF andDMSO) showed the characteristic red shifted Q band andvibrational absorptions in the range of 718–752 and639–676 nm, respectively, which can be attributed to the π→π*transitions from the highest occupied molecular orbital(HOMO) to the lowest unoccupied molecular orbital (LUMO)of the Pc ring (Fig. 1 and Table 1). The broad bands in therange of 494–531 nm are probably due to charge transfer fromthe electron-rich ring to the electron-poor metal center.25,26

The other B bands in the UV range 288–313 nm were due totransitions from the deeper π levels to the LUMO (Fig. 1 andTable 1). The UV-vis spectra of 2.0 × 10−6 M 5–8 in various sol-vents exhibited sharp and non-split Q-band absorptions which

are characteristic of monomeric metal Pcs. The non-aggregat-ing behaviors of the complexes at the specified concentrationmay be due to the existence of the axial chlorine ligand, whichreduces the π→π* interaction between two macrocycle units.27

Positions of the Q bands of MPc complexes are closely relatedto the refractive indices of the solvents.28 The higher the refrac-tive index of the solvent, the more red-shifted the Q band ofthe MPc complex concerned. The Pcs 5, 6, 7 and 8 had the Qbands at 740, 720, 718 and 726 nm, respectively, in THF with arefractive index of 1.406 while these compounds displayed theQ bands at 748, 727, 724 and 730 nm, respectively, in DMSOwith a refractive index of 1.479. Thus, the replacement of thesolvent with the one with higher refractive index resulted inthe red-shift of the Q-band in the range of 4–8 nm (Fig. 1 andTable 1). The molecular ion peak for MnPcs 5–8 was notobserved in their MALDI-TOF mass spectra. However, the basepeaks corresponding to the cleavage of the axial M–Cl bondwere detected. These peaks of the MnPcs 5–8 appeared at1687.794, 1687.616, 1823.352 and 2807.762 Da, respectively.Besides the M–Cl+ peaks of the complexes, sodium and potass-ium ion adducts were also monitored. Complex 8 displayedmore than one sodium adduct peak, indicating that thesodium selectivity of this complex was higher than that of theothers. It appears that the abundance and nature of substitu-ents on the periphery affect the sodium selectivity of thecomplex. Potassium ion adducts were also observed in thespectra of 5 and 6. Furthermore, all the complexes showedCH3 and axially chlorine fragmentation under the MALDI-TOFmass spectroscopy conditions in the reflectron mode. All high

Fig. 1 Electronic absorption spectra of 2.0 × 10−6 M (A) 5, (B) 6, (C) 7 and (D) 8 in different solvents.



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resolved experimental peaks matched perfectly the theoreticalpeaks of the complexes determined by isotropic software calcu-lation. Thus, MALDI-TOF mass spectroscopy analyses con-firmed the structures of all Pc samples. The spectra of 6 and 7are given in Fig. 2 as examples.

3.2. Electrochemistry and in situ spectroelectrochemistry

Table 2 sums up cyclic voltammetry of the complexes rep-resented by the half-wave potentials (E1/2), anodic to cathodicpeak potential separations (ΔEp) and the assignments of theobserved redox couples. ΔEp values at 0.010 V s−1 scan ratewere in the range of 0.050 to 0.150 V reflecting reversible orquasi-reversible behaviour.

Cyclic voltammograms of beta tetra coumarin substitutedcomplex 6 in DMSO at various scan rates are shown in Fig. 3A.The compound gives three reversible or quasi-reversiblereduction couples (R1, R2 and R3) with anodic to cathodicpeak separations in the range of 0.050–0.150 V at 0.025 V s−1

scan rate and the relevant half-wave potentials listed in

Table 1 UV-vis spectral data for 2.0 × 10−6 mol dm−3 5–8 in various solvents

Solvent PcsQ-band,λmax/nm Log ε

Charge transferband, λmax/nm Log ε

B-band,λmax/nm Log ε

Toluene 5 751, 673 6.080, 5.283 518 5.100 313 5.825DCM 5 752, 676 6.025, 5.369 531 5.246 288 5.981THF 5 740, 668 5.996, 5.283 507 5.025 295 5.827DMSO 5 748, 674 5.968, 5.438 512 5.220 291 5.943




Fig. 2 Positive ion and reflectron mode MALDI-TOF-MS spectrum of (A)6 and (B) 7 in the α-cyano-4-hydroxycinnamic acid MALDI matrix using anitrogen laser (at 337 nm wavelength) accumulating 50 laser shots.

Table 2 The electrochemical data for 5–8

Pcs Redox processes

aE1/2(V vs. SCE)

bΔEp(V)

5 Mn(III)Pc(−2)Cl−/[Mn(II)Pc(−2)Cl−]− R1 0.120 0.065Mn(II)Pc(−2)/[Mn(I)Pc(−2)] cR2′ −0.601 0.070[Mn(II)Pc(−2)Cl−]−/[Mn(I)Pc(−2)] cR2′′ −0.975 0.150[Mn(I)Pc(−2)]−/[Mn(I)Pc(−3)]2− R3 −1.286 0.055[Mn(I)Pc(−3)]2−/[Mn(I)Pc(−4)]3− R4 −1.625 0.110

6 Mn(III)Pc(−2)Cl−/Mn(II)Pc(−2) R1 0.090 0.050Mn(II)Pc(−2)/[Mn(I)Pc(−2)]− R2 −0.525 0.150[Mn(I)Pc(−2)]−/[Mn(I)Pc(−3)]2− R3 −1.104 0.060



a E1/2 = (Epa + Epc)/2 at 0.025 V s−1. bΔEp = Epa − Epc at 0.025 V s−1.c Electrochemical measurements imply the establishment of anequilibrium between [Mn(II)Pc(−2)Cl−]− and Mn(II)Pc(−2) species.Couples R2′ and R2′′ are assigned to the reduction of [Mn(II)Pc(−2)]and [Mn(II)Pc(−2)Cl−]− species, respectively, since the latter species areexpected to be reduced at a potential more negative than that of theformer ones, due to its negative charge.



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Table 2. The voltammetric peaks are considerably roundedsuggesting the presence of aggregated species in the solution.The aggregation tendency of this complex can be attributed toits planarity. The first reduction process R1 probably corre-sponds to Mn(III)Pc(−2)Cl−/Mn(II)Pc(−2) and therefore, Cl−

leaves [Mn(II)Pc(−2)Cl−]− quickly after the electron transfersince the peak is not split. Fig. 3B shows in situ UV-vis spectral

changes during the first reduction process of 6 in de-aeratedDMSO/TBAP solutions at −0.20 V vs. SCE. The presence of aband at 630 nm in the original spectrum of 6 monitoredbefore the electrolysis implies that there is μ-oxo species in thesolution although it is deaerated. Throughout the electrolysis,the complete disappearance of the bands at 729 nm and500 nm is observed. These spectral changes are accompaniedby an increase in the band at 630 nm and the shifting of the Bband from 310 to 326 nm. It was very interesting to observethat the disappearance of the Q band at 729 nm was notaccompanied by the formation of a band around 700 nmcorresponding to Mn(II)Pc(−2) species.26,29–33 This observationstrongly suggests that Mn(II)Pc(−2) species produced duringthe first reduction readily forms μ-oxo MnPc species and thus,that the R2 process corresponds to the reduction of μ-oxoMnPc species. Lever et al. reported previously that Mn(II)Pcspecies has high tendency of forming μ-oxo MnPc species.34

Nyokong et al. reported previously that Mn(II)Pc species hashigh tendency of forming μ-oxo MnPc species.26 According totheir idea, these species may be produced, even during the vol-tammetric measurements carried out in deaerated solutions,due to the O2 entered in the cell or trace amounts of O2 thatcould not be removed from the solution.26 In situ spectralchanges during the electrolysis at −0.83 V vs. SCE are shown inFig. 3C. Upon the second reduction, the band at 630 nmcorresponding to μ-oxo MnPc species nearly disappears whilea new band at 532 nm, reflecting the formation of [Mn(I)-Pc(−2)]− species, forms.32,33,35 The third reduction in theMn(III)Pc(−2)Cl− complexes, R3 in Fig. 3C, is attributed to the[Mn(I)Pc(−2)]/[Mn(I)Pc(−3)]2− couple.

Cyclic voltammograms of alpha-substituted Mn(III)Pc(−2)-Cl−, 5, is shown in Fig. 4A. The voltammetric signals of 5 aresharper than those of 6. This should be due to lower aggrega-tion tendency of 5, probably as a result of deviation from pla-narity. Four main reduction processes, labelled R1, R2, R3 andR4, were observed. The relevant half-wave potentials are listedin Table 2. The redox behavior of Mn(III)Pc(−2)Cl− complexesreported previously in the literature implies that process R1corresponds to Mn(III)Pc(−2)Cl−/Mn(II)Pc(−2).26,29–33,36 Thesecond reduction process is split into two couples, labelled asR2′ and R2″. The anodic peak of process R2″ is observed onlyat the scan rates higher than 0.050 V s−1. This behaviour isprobably due to the establishment of equilibrium between the[Mn(II)Pc(−2)Cl−]− and [Mn(II)Pc(−2)] species after the firstreduction process. Here, R2′ should belong to the reduction of[Mn(II)Pc(−2)] species while R2″ probably represents thereduction of [Mn(II)Pc(−2)Cl−]− ions, since the latter ones withthe negative charge are anticipated to be reduced less easilywith respect to that of the former species. Two different situ-ations are possible for the second reduction in Mn(III)Pc(−2)Cl− complexes. Some reports proposed ring reduction to Mn(II)Pc(−3)26,29–33 and others suggested metal reduction to Mn(I)-Pc(−2).32,33,37 Furthermore, it is well known from the relevantliterature that the formation of µ-oxo MnPc species may followthe first reduction to Mn(II)Pc(−2) as a result of the interactionwith O2.

28,34 In contrast to beta-substituted complex 6, alpha-

Fig. 3 (A) Cyclic voltammograms of O2-removed solution of 6 on Pt inTBAP/DMSO. In situ UV-vis spectral changes during (B) the firstreduction and (C) the second reduction processes of 6 in O2-removedTBAP–DMSO.



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substituted complex 5 did not form µ-oxo MnPc in deaeratedelectrolyte solution under the possibility of the presence oftrace amounts of O2, presumably due to the hindrance of inter-actions with O2 by the non-peripheral nature of alpha substitu-ents. Fig. 4B shows in situ UV-vis spectral changes during thefirst reduction process of 5 in deaerated DMSO/TBAP solution.Upon the first reduction, the Q band absorption at 751 nmdecreases whereas the new bands at 583, 655, 698 and 900 nmform. The decrease in the Q band and newly formed bands in

the charge transfer region confirms the production of Mn(II)-Pc(−2) species.26,29–33 The bands at 655 and 698 nm presum-ably correspond to Mn(II)Pc(−2) and [Mn(II)Pc(−2)Cl−]− speciesand are compatible with the voltammetric assignment ofcouples R2′ and R2″ to the reductions of Mn(II)Pc(−2) and[Mn(II)Pc(−2)Cl−]− species, respectively. The bands observed at583 and 900 nm reflect charge transfer transitions of mono-reduced species. The spectral changes observed during thefirst reduction process do not involve the formation of a bandaround 640 nm. This observation confirms that Mn(III)Pc–O–PcMn(III) species do not form.26,33,35 During the reduction at−1.20 V vs. SCE in O2-removed solution, the band at 751 nmnearly disappears while those at 583, 698 and 900 nm changewithout any shift (Fig. 4C). At the same time, the bands at 513and 583 nm shift to 521 and 561 nm, respectively. The bandsat 521 and 561 nm are probably due to the formation of [Mn(I)-Pc(−2)]− species. Fig. 5A shows the cyclic voltammograms of 5,recorded during the oxygenation of its de-aerated solutionslowly. The voltammograms suggest that the first reductionprocess of 5 is followed by the formation of µ-oxo MnPcspecies when the deaerated solution is purged previously withO2. Accordingly, the controlled-potential electrolysis of the O2

involving Mn(III)Pc(−2)Cl− solution under air gives twodifferent groups of spectral changes in comparison with thoseobserved for the O2-removed solution. Upon the reduction at−0.15 V vs. SCE, first, the absorptions of the Q and B bands at751 nm decrease; however, the original Q band does not dis-appear (Fig. 5B). These spectral changes are followed by dis-appearance of the Q band, the formation of new bands at 645and 706 nm, and the shift of the B band with an increase inabsorption (inset in Fig. 5B). These spectral changes indicatethat the first reduction process is also from Mn(III)Pc(−2)Cl− to[Mn(II)Pc(−2)Cl−]−. However, in contrast to the observationswith O2-removed solution, complete transformation fromMn(III)Pc(−2)Cl− to [Mn(II)Pc(−2)Cl−]− is followed first by theleaving of chloride ions readily and then the formation ofMn(III)Pc–O–PcMn(III) species with the establishment of theequilibrium with Mn(II)Pc(−2) species. Furthermore, the com-parison with the spectroelectrochemical behaviour of 6 inaerated solution shows that the tendency of alpha tetra-cou-marin substituted 5 to form μ-oxo species is much less thanbeta tetra-coumarin substituted 5. Fig. 5C shows the spectralchanges during the electrolysis at −1.10 V versus SCE. Mainly,the absorption of the band at 706 nm decreases while two newbands form at 522 and 870 nm. These bands are due to theMn(II)/Mn(I) process. However, there is still μ-oxo MnPc speciesin the solution, suggesting its high stability. Further reductionat −1.50 V versus SCE leads to the decrease in the bands at 706and 645 nm, and the formation of a new band at 567 nm,which is characteristic of the ligand-based [Mn(I)Pc(−2)]−/[Mn(I)Pc(−3)]2− couple.

3.3. Photovoltaic measurements

A number of photovoltaic devices with the structure ITO/C60/Pc/Al using the manganese Pcs 5–8 in Scheme 1 as donormaterials were fabricated. The current density–voltage ( J–V)

Fig. 4 (A) Cyclic voltammograms of O2-removed solution of 5 on Pt inTBAP–DMSO. In situ UV-vis spectral changes (B) at −0.22 V and (C) at−1.20 V vs. SCE in O2-removed TBAP/DMSO.



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characteristics of the fabricated devices were measured inambient air under an illumination of 100 mW cm−2 with anAM1·5G sun simulator, with the aim of determining the per-formance parameters, such as open circuit voltage, fill factor,etc., of a solar cell under the conditions of illumination equi-valent to the sunlight. The illumination ( J–V) characteristics ofthe produced photovoltaic devices with 5–8 as the donor layerare shown in Fig. 6. It is clear that all devices exhibit rectifyingdiode characteristics as expected from heterojunction devicessandwiched between electrodes having different work func-tions. It is also clear from Fig. 6 that the overall shape of themeasured J–V curves under reverse and forward bias of thedevices changes considerably. The summary of device para-meters Voc, Isc, FF, and η for all devices investigated in thisstudy is given in Table 3. The photovoltaic conversionefficiency of the ITO/5/C60/Al structure is 0.039%, with an opencircuit voltage of 0.45 V, a short circuit current of 0.26 mAcm−2, and a fill factor of 33%. The most enhanced η, 0.191%,was measured for the ITO/8/C60/Al structure (Voc = 0.73 V, Jsc =0.81 mA cm−2, FF = 32%), exhibiting a 390% increase in η over

Fig. 5 (A) Cyclic voltammograms of O2-removed solution of 5 on Pt in DMSO–TBAP, during the passage of O2 gas for different times. In situ UV-visspectral changes during the controlled-potential electrolysis of O2-involving solution of 5 (B) at −0.15 V, (C) at −1.10 V, and (D) at −1.50 V vs. SCE inTBAP–DMSO.

Fig. 6 Current density vs. voltage (J–V) characteristics of four photo-voltaic devices with the structure of ITO/5–8 (30 nm)/C60 (30 nm)/Al(400 nm) under AM1.5 illumination.



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the structure of the ITO/5/C60/Al. These improvements in thephotovoltaic performance of the devices suggest that there issignificant modification of band structures of the donormaterial caused by the change in substituent groups and theirposition.

Indeed, the open circuit voltage is a critical factor in deter-mining the efficiency of organic solar cells and is still an openissue. In spite of the absence of a satisfactory model describ-ing the origin of the open circuit voltage in donor–acceptorheterojunction photovoltaic devices, metal–insulator–metal(MIM) and highest occupied molecular orbital (HOMO)–lowestunoccupied molecular orbital (LUMO) models for the observedopen circuit voltage still appear to be adequate. According tothe MIM model, a built-in electric field is established by theelectrode work function differential and the work functiondifference of the two electrodes defines the upper limit of theVoc. The MIM model also assumes a negligible intrinsic chargecarrier in the active organic layers and predicts a uniform elec-tric field, F, throughout the device thickness in the absence ofspace charge. If the mechanism responsible for the observedopen circuit voltage can be treated by the MIM model, thedevices should yield a maximum Voc of 0.4 V (Al 4.3 eV andITO 4.7 eV) irrespective of the substituent group and its posi-tion in the donor material. As can be seen clearly from Fig. 6and Table 3, the dependence of the Voc on the substituentgroup’s position does not indicate the applicability of the MIMmodel in the investigated devices. On the other hand, Brabecet al. have shown that the Voc is independent of the choice ofcathode material.38 Several recent reports on planar hetero-junction39 as well as bulk heterojunction40,41 solar cells haveshown that the Voc is strongly dependent on the differencebetween the HOMO of the donor and the LUMO of the accep-tor materials. It is proposed that the structure, morphology,and absorption properties of the evaporated film of the donormaterials and the efficient separation of charges at the donor–acceptor interface in bilayer planar and non-planar metal Pc/C60 solar cells are also crucial in determining the Voc value.The open circuit voltage (Voc) lines up in the order of 8 > 7 > 6> 5 between 0.45 V and 0.73 V. Probably, the energy of theHOMO of the compounds also changes in the order of 8 > 7 >6 > 5 since it is well known that substituents can change theenergetic position of the HOMO, and thus, the energy differ-ence between the HOMO of the donor and the LUMO of theacceptor, via mesomeric or inductive effects.42

One of the other key parameters of a solar cell is the short-circuit current. The short-circuit current ( Jsc) of a photovoltaicdevice is generally considered as a combined measure of the

dissociation of photogenerated excitons into free charge car-riers at the donor–acceptor interface. It is well established thatthe current generation in an organic photovoltaic cell requiresthree basic attributes; light is absorbed in either of two donor(D) or acceptor (A) layers, creating excited states (excitons),diffusion and dissociation of these neutral excitons into freecharge carriers before they recombine either radiatively or non-radiatively. Recombination causes a loss of the carrier andaffects the performance of the cell. Therefore, exciton dis-sociation and charge transport to the appropriate electrodesare the most important determining factors of photo-conver-sion efficiency. Because of their large binding energy, theseexcitons can only dissociate in the presence of an electric fieldor at a donor–acceptor interface where the dissociation isdriven by charge transfer between the donors and acceptors.43

For efficient exciton dissociation, HOMO and LUMO energydifferences formed by the donor–acceptor junction have to bebigger than the exciton binding energy. In order to gain moreinsight into the photo-physics of the devices and optimize thecell performance, the effect of the thickness of the active Pclayer on solar cell parameters has also been investigated.Complex 8 has been chosen for the investigation of the thick-ness dependence of the performance parameters. The thick-ness of the 8 layer was varied from 30 nm to l70 nm. Fig. 7compares the current density versus voltage ( J–V) character-istics of various cells prepared using different thicknesses ofthe Pc layers under 100 mW cm−2 illumination and the deviceperformance parameters are summarized in Table 4 fornumerical comparison. A close investigation of Fig. 7 indicatesthat, although the open circuit voltages of all devices are about0.75 V irrespective of the thickness of the Pc layer, the shortcircuit current of the same cells increases dramatically withthe thickness of the Pc layer. Recently, Kooistra et al.44 havediscussed that the energy difference between the HOMO of thedonor and the LUMO of the acceptor is closely correlated with

Table 3 Structure and photovoltaic parameters of the investigatedsolar cells with a 30 nm Pc layer thickness

Device Jsc (mA cm−2) Voc (V) FF η (%)

ITO/5/C60/Al 0.26 0.45 0.33 0.039ITO/6/C60/Al 0.40 0.53 0.34 0.070ITO/7/C60/Al 0.66 0.67 0.36 0.160ITO/8/C60/Al 0.81 0.73 0.32 0.191

Fig. 7 J–V characteristics of the ITO/8/C60/Al photovoltaic devices atdifferent thicknesses of the film of 8.



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the observed open circuit value. Therefore, a thickness inde-pendent Voc is expected because the Voc depends mostly on theenergy levels of the donor and acceptor materials. There arealso many reports on increasing the Voc by changing the thick-ness of the Pc layer, in contrast to our observation. The effectof the CuPc layer thickness on the open circuit voltage andshort circuit current in ITO/PEDOT:PSS/CuPc/Al solar celldevices was investigated by Rajaputra et al.45 They concludedthat the enhancement in the Voc with the thickness is primar-ily due to the enhanced Jsc and not due to the reduced reversesaturation current density. It should be noted that not only Iscbut also the other photovoltaic parameters show a strongdependence on the Pc layer thickness; the photovoltaic conver-sion efficiency increases with increasing Pc layer thicknessreaching a value of 0.532% for an 8 layer thickness of 170 nm.The increase in Isc and η with the Pc layer thickness can beattributed to the following two reasons: it is well known thatthe Pc is a good absorber of visible light of 550–800 nm, anincrease in the thickness of the photoactive layer leads to agreater absorption and hence more excision generation, whichin turn leads to an enhanced photovoltaic performance.Another possible reason for the improved photovoltaic per-formance in the thicker active layer is the change in the degreeof crystallinity, grain size and stacking arrangement of the Pcmolecules with increasing film thickness. Senthilarasu et al.46

demonstrated how the film thickness rearranges the molecularstacks. They observed that the degree of crystallinity and thegrain size increase with the film thickness. The increase in thedegree of crystallinity and the grain size may result in alteringthe interaction of the π-electron systems between the differentmolecules, which may affect the photovoltaic performance ofthe cells.

4. Conclusions

The novel Mn(III)Pcs 5, 6, 7 and 8 have been prepared from3-(4-(4-methoxyphenyl)-8-methyl-coumarin-7-oxy)phthalonitrile1, 4-(4-(4-methoxyphenyl)-8-methylcoumarin-7-oxy)phthalo-nitrile 2, 4-chloro-5-(4-(4-methoxyphenyl)-8-methylcoumarin-7-yloxy)phthalonitrile 3 and 4,5-bis(4-(4-methoxyphenyl)-8-methylcoumarin-7-yloxy)phthalonitrile 4, respectively. Thecompounds were characterized by UV-vis, IR and MALDI-TOFmass spectrometry, and elemental analysis. The effects of sub-stituent (the coumarin and chloro) and solvent (DMSO, DCM,toluene and chloroform) on the spectroscopic properties and

aggregation behaviour of the novel compounds were investi-gated. Spectroscopic studies of the complexes show that non-aggregated species for the compounds were formed because ofthe existence of the axial chlorine ligand. Both ligand- andmetal-based reduction processes of manganese Pc compoundswere observed in TBAP/DMSO. The central metal of the betacoumarin substituted complex was observed to interact moreeffectively with dioxygen in comparison with the alpha coumarinsubstituted one, probably due to the hindrance of the inter-action by the nonplanarity in the case of alpha substitution. Theaggregation tendency of the alpha coumarin substitutedcomplex was also observed to be lower than that of the beta cou-marin substituted one. The synthesised compounds have beeninvestigated for organic solar cell applications. The devices con-sisted of an indium tin oxide (ITO) coated glass substrate, C60 asthe acceptor, a Pc layer as the donor, and an aluminum (Al) elec-trode. It has been found that the ITO/C60/8/Al cell exhibits thebest performance. To investigate the influence of the active layerthickness on the cell performance, cells with several differentthicknesses were fabricated. It was found that the performanceof the ITO/C60/8/Al photovoltaic devices can be improved by theoptimization of the thickness of the Pc layer. It can be said thatcompound 8 has good potential for photovoltaic applications.

Acknowledgements

We are thankful to Marmara University, Scientific ResearchCommission for the financial support (Project no:FEN-A-130511-0159 and FEN-A-150513-0164). ARÖ also thanksthe Turkish Academy of Sciences (TUBA) for the partial finan-cial support.

Notes and references

1 The Phthalocyanines, Properties and Applications, ed.C. C. Leznoff and A. B. P. Lever, VCH, New York, 1989–96.

2 N. B. McKeown, in Phthalocyanines Materials-Synthesis,Structure and Function, Cambridge University Press,New York, 1998.

3 N. McKeown, Comprehensive Coordination Chemistry II, Else-vier Science Publishers, Amsterdam, 2003.

4 M. Tanaka, Phthalocyanines, in High Performance Pigmentsand their Applications, ed. E. B. Faulkner and R. J. Schwartz,Wiley-VCH, Weinheirn, Germany, 2009, pp. 276–290.

5 B. C. O’Regan, I. L. Duarte, M. V. M. Día, A. Forneli,J. Albero, A. Morandeira, E. Palomares, T. Torres andT. J. R. Durrant, J. Am. Chem. Soc., 2008, 130, 2906.

6 İ. Koç, M. Özer, A. R. Özkaya and Ö. Bekaroğlu, DaltonTrans., 2009, 6368–6376.

7 A. Koca, T. Ceyhan, M. K. Erbil, A. R. Özkaya andÖ. Bekaroğlu, Chem. Phys., 2007, 340, 283.

8 C. C. Leznoff, S. Black, A. Hiebert, P. W. Causey,D. Christendat and A. B. P. Lever, Inorg. Chim. Acta, 2006,359, 2690.

Table 4 Thickness dependence of the photovoltaic performance ofthe ITO/C60/8/Al device

Thickness (nm) Isc (mA cm−2) Voc (V) FF η (%)

30 0.81 0.73 0.32 0.19160 1.16 0.74 0.32 0.277100 1.62 0.74 0.31 0.375130 1.93 0.76 0.32 0.474170 2.10 0.76 0.33 0.532



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57:4

0.

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9 P. M. Bumham, M. J. Cook, L. A. Gerrard, M. J. Heeney andD. L. Hughes, Chem. Commun., 2003, 2064.

10 T. Fukuda, T. Ishigura and N. Kobayashi, Tetrahedron Lett.,2005, 46, 2907.

11 N. Kobayashi, in Phthalocyanines: Properties and Appli-cations, ed. C. C. Leznoff and A. B. P. Lever, Wiley-VCHPublishers Inc., New York, 1992, vol. 2.

12 A. K. Sobbi, D. Wöhrle and D. Schlettwein, J. Chem. Soc.,Perkin Trans. 2, 1993, 48.

13 N. Kobayashi, in Phthalocyanines: Properties and Appli-cations, ed. C. C. Leznoff and A. B. P. Lever, VCH PublishersInc., New York, 1993, vol. 3, pp. 97–162.

14 A. Kotali, I. S. Lafazanis and P. A. Haris, Tetrahedron Lett.,2007, 48, 7181.

15 F. F. Ye, J. R. Gao, W. J. Sheng and J. H. Jia, Dyes Pigm.,2008, 77, 556.

16 N. Periera Rodrigues, J. Obirai, T. Nyokong and F. Bedioui,Electroanalysis, 2005, 17, 186.

17 J. Obirai and T. Nyokong, Electrochim. Acta, 2005, 50, 5427.18 Z. Odabaş, H. Kara, A. R. Özkaya and M. Bulut, Polyhedron,

2012, 39, 38.19 S. Altun, A. R. Özkaya and M. Bulut, Polyhedron, 2012, 48, 31.20 M. Kandaz, A. R. Özkaya and Ö. Bekaroglu, Monatsh.

Chem., 2001, 132, 1013.21 H. Spanggaard and F. C. Krebs, Sol. Energy Mater. Sol. Cells,

2004, 83, 125.22 Y. Yoshida, M. Nakamura, S. Tanaka, I. Hiromitsu, Y. Fujita

and K. Yoshino, Synth. Met., 2006, 156, 1213.23 Z. Odabaş, B. E. Orman, F. Dumludağ, M. Durmuş,

A. R. Özkaya and M. Bulut, Dyes Pigm., 2012, 95, 540.24 A. Erdoğmuş, I. A. Akınbulu and T. Nyokong, Polyhedron,

2010, 29, 2352.25 I. Yılmaz, New J. Chem., 2008, 32, 37.26 J. Obirai and T. Nyokong, Electrochim. Acta, 2005, 50, 3296.27 M. J. Stillman, in Phthalocyanines: Properties and Appli-

cations, ed. C. C. Leznoff and A. B. P. Lever, Wiley-VCH,New York, 1993, vol. 3.

28 A. Ogunsipe, M. Durmuş, D. Atilla, A. G. Gürek, V. Ahsenand T. Nyokong, Synth. Met., 2008, 158, 839.

29 C. C. Leznoff, L. S. Black, A. Hiebert, P. W. Causey,D. Christendant and A. B. P. Lever, Inorg. Chim. Acta, 2006,359, 2690.

30 B. Agboola, K. I. Ozoemena, P. Westbroek and T. Nyokong,Electrochim. Acta, 2007, 52, 2520.

31 G. Mbambisa, P. Tau, E. Antunes and T. Nyokong, Polyhe-dron, 2007, 26, 5355.

32 N. Sehlotho, M. Durmus, V. Ahsen and T. Nyokong, Inorg.Chem. Commun., 2008, 11, 479.

33 C. L. Lin, C. C. Lee and K. C. Ho, J. Electroanal. Chem.,2002, 524, 81.

34 A. B. P. Lever, J. P. Wilshire and S. K. Quan, Inorg. Chem.,1981, 20, 761.

35 M. Kandaz and A. Koca, Polyhedron, 2009, 28, 2933.36 T. Fukuda, K. Yamamota and N. Kobayashi, J. Porphyrins

Phthalocyanines, 2013, 17, 756.37 A. T. Bilgiçli, M. N. Yaraşır, M. Kandaz and A. R. Özkaya,

Polyhedron, 2010, 29, 2498.38 C. J. Brabec, A. Cravino, D. Meissner, N. S. Sariciftci,

T. Fromherz, M. T. Rispens, L. Sanchez andJ. C. Hummelen, Thin Solid Films, 2002, 403, 368.

39 B. P. Rand, D. P. Burk and S. R. Forrest, Phys. Rev. B:Condens. Matter, 2007, 75, 115327.

40 M. C. Scharber, D. Wuhlbacher, M. Koppe, P. F. Denk,C. Waldauf, A. J. Heeger and C. L. Brabec, Adv. Mater.,2006, 18, 789.

41 V. D. Mihailetchi, P. W. M. Blom, J. C. Hummelen andM. T. Rispens, J. Appl. Phys., 2003, 94, 6849.

42 G. Horowitz, J. Mater. Res., 2004, 19, 1946.43 C. Lungenschmied, G. Dennler, H. Neugebauer,

N. S. Sariciftci and E. Ehrenfreund, Appl. Phys. Lett., 2006,89, 223519.

44 F. B. Kooistra, J. Knol, F. Kastenberg, L. M. Popescu,W. J. H. Verhees, J. M. Kroon and J. C. Hummelen, Org.Lett., 2007, 9, 551.

45 S. Rajaputra, S. Vallurupalli and V. P. Singh, J. Mater. Sci.Mater. Electron., 2007, 18, 1147.

46 S. Senthilarasu, Y. B. Hahn and S. H. Lee, J. Appl. Phys.,2007, 102, 43512.



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Documents

Coumarin-substituted manganese phthalocyanines: synthesis, characterization, photovoltaic behaviour, spectral and electrochemical properties