Synthesis, spectroscopic characterization and thermogravimetric analysis of two series of substituted (metallo)tetraphenylporphyrins

  1. Rasha K. Al-Shewiki1,
  2. Carola Mende1,
  3. Roy Buschbeck1,
  4. Pablo F. Siles2,3,
  5. Oliver G. Schmidt2,3,
  6. Tobias Rüffer1 and
  7. Heinrich Lang1

1Inorganic Chemistry, Institute of Chemistry, Faculty of Natural Sciences, TU Chemnitz, 09107 Chemnitz, Germany
2Material Systems for Nanoelectronics, TU Chemnitz, 09107 Chemnitz, Germany
3Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany

  1. Corresponding author email

This article is part of the Thematic Series "Towards molecular spintronics".

Guest Editor: G. Salvan
Beilstein J. Nanotechnol. 2017, 8, 1191–1204. doi:10.3762/bjnano.8.121
Received 24 Feb 2017, Accepted 11 May 2017, Published 02 Jun 2017

Abstract

Subsequent treatment of H2TPP(CO2H)4 (tetra(p-carboxylic acid phenyl)porphyrin, 1) with an excess of oxalyl chloride and HNR2 afforded H2TPP(C(O)NR2)4 (R = Me, 2; iPr, 3) with yields exceeding 80%. The porphyrins 2 and 3 could be converted to the corresponding metalloporphyrins MTPP(C(O)NR2)4 (R = Me/iPr for M = Zn (2a, 3a); Cu (2b, 3b); Ni (2c, 3c); Co (2d, 3d)) by the addition of 3 equiv of anhydrous MCl2 (M = Zn, Cu, Ni, Co) to dimethylformamide solutions of 2 and 3 at elevated temperatures. Metalloporphyrins 2ad and 3ad were obtained in yields exceeding 60% and have been, as well as 2 and 3, characterized by elemental analysis, electrospray ionization mass spectrometry (ESIMS) and IR and UV–vis spectroscopy. Porphyrins 2, 2ad and 3, 3ad are not suitable for organic molecular beam deposition (OMBD), which is attributed to their comparatively low thermal stability as determined by thermogravimetric analysis (TG) of selected representatives.

Keywords: electrospray ionization mass spectrometry; IR spectroscopy; metalloporphyrin; porphyrin; thermogravimetry; UV–vis spectroscopy

Introduction

Over the last decades metalloporphyrins have been studied in great detail as they exhibit a high chemical and thermal stability, are aromatic and possess distinctive electrochemical and photophysical properties [1-4]. For example, access to the first organic spin valves, which were based on tris(8-hydroxyquinolinato)aluminium (Alq3) sandwiched between La2/3Sr1/3MnO3 and cobalt electrodes, was reported more than a decade ago [5]. This finding motivated the development of further novel devices as, for example, spin-OFETs (organic field effect transistors) [4]. The nature of the molecules integrated into spintronic devices ranges from purely diamagnetic molecules to individual single molecule magnets (SMMs) [4]. Among such molecules metalloporphyrins are very promising in terms of diverse applications [4]. Recently, we reported on the deposition of thin films of porphyrins of the type H2TPP(OH)4 (tetra(p-hydroxyphenyl)porphyrin) [6,7] and MTPP(OMe)4/H2TPP(OMe)4 (tetra(p-methoxyphenyl)porphyrin) (M = Cu [8,9], Ni [9]), cf. Figure 1.

[2190-4286-8-121-1]

Figure 1: Chemical structures of porphyrins and metalloporphyrins successfully deposited by organic molecular beam deposition.

The properties of the metalloporphyrins are governed by the (transition) metal ions and the exocyclic moieties on the individual pyrrole fragments and/or on the meso positions. Comparative studies of the accessibility and characterization of metalloporphyrins are scarcely reported in literature [1-3,10-12], which limits, for example, the possibility to select a certain metalloporphyrin with respect to a desired property by a knowledge-based approach. Along with a preliminary work of us, we noticed that “[…]the electrical analysis and the understanding of the underlying transport mechanism become important for future implementation of porphyrin-based (spintronic) devices.[…]” [8]. It was thus desired to have access to metalloporphyrins of which the central metal ion varies on the one hand, while on the other hand these metalloporphyrins should be sterically more demanding to vary the film morphology compared to our original report [8]. In order to support the idea that different central metals as well as sterically more demanding substituents will vary film morphologies one can, for example, inspect the results of the single-crystal crystallographic characterization even of the compounds displayed in Figure 1. It is instructive to notice, that for ZnTPP(OMe)4 [13] the formation of 2D layers is observed in which symmetry-related molecules with planar porphyrin cores interact with each other by, for example, formation of intermolecular ZnII…O contacts. Further intermolecular interactions refer to those that were described in detail by, for example, Goldberg et al. [14] or by us [15]. In contrast, saddle-shape distorted molecules of CuTPP(OMe)4 are described as interacting via C–Hπ and C–HO bonds to give a 3D supramolecular motif [16]. Furthermore, if one substitutes the terminal methyl substituents of H2TPP(OMe)4 (Figure 1) by sterically more demanding substituents as reported for H2TPP(OR)4 (OR = p-(N-n-butylcarbamoyl)methoxyphenyl) [17] one decreases the density to the materials to ρ = 1.036 g/cm3 compared to ρ = 1.491 g/cm3 for ZnTPP(OMe)4 [13] or ρ = 1.398 g/cm3 for CuTPP(OMe)4 [16].

Thus, we report herein on two novel series of (metallo)porphyrins of the type H2/MTPP(C(O)N(R)2)4 (R = Me, with H2TPP(C(O)NMe2)4 (2) and MTPP(C(O)N(iPr)2)4 (M = Zn (2a), Cu (2b), Ni (2c), Co (2d); R = iPr, with H2TPP(C(O)N(iPr)2)4 (3) and MTPP(C(O)N(iPr)2)4 (M = Zn (3a), Cu (3b), Ni (3c), Co (3d)). The aim of this report is not only to describe their synthesis and characterization (ESIMS, FTIR, NMR, UV–vis) but also to study to which extend these new (metallo)porphyrins are suitable to be deposited in form of thin films by OMBD. Therefore, the thermal stabilities derived from TG studies of selected representatives of 2/2ad and 3/3ad in comparison with that of H2TPP(OH)4 [6,7] will be discussed together with the results of OMBD studies.

Results and Discussion

Synthesis

Porphyrins 2 and 3 were synthesized as shown in Scheme 1 according to a procedure reported by Gradl et al. [18]. Literature-known H2TPP(CO2H)4 (1) was treated first with an excess of oxalyl chloride in dichloromethane in the presence of dimethylformamide. As we used a larger amount of dimethylformamide as indicated in [18], the yields of 2 and 3 could be increased significantly. This is attributed to the solubility of 1 in dimethylformamide. The addition of a large excess of the mild chlorinating agent oxalyl chloride converted 1 to H2TPP(C(O)Cl)4 (Scheme 1) which further reacted with the secondary amines HNMe2 and HN(iPr)2 to give 2 (H2TPP(C(O)NMe2)4) and 3 (H2TPP(C(O)N(iPr)2)4). The molar excess of oxalyl chloride compared to 1 should be above 25:1, as otherwise 1 cannot be fully converted to H2TPP(C(O)Cl)4. However, the use of thionyl chloride to convert 1 to H2TPP(C(O)Cl)4 is accompanied by chlorination of the β-pyrrolic positions. After formation of H2TPP(C(O)Cl)4 all volatiles must be removed in vacuum in order to avoid, for example, unwanted reactions upon the addition of HNMe2 and HN(iPr)2. Appropriate work-up, gave 2 and 3 in yields exceeding 80% without any column-chromatographic purification (cf. Experimental section).

[2190-4286-8-121-i1]

Scheme 1: Synthetic methodology to prepare (metallo)porphyrins 2, 2a–d and 3, 3a–d.

The metalation reactions performed in this study correspond to the well-known “dimethylformamide method” (MII = Zn, Cu, Ni, Co), cf. Scheme 1 and [19]. In agreement with details reported for the dimethylformamide method, “[…]best results have been obtained with anhydrous metal chlorides[…]” [19], although the reaction temperatures should be kept at 140 °C. According to [19], complete metalation needs the subsequent addition of an excess of the metal chlorides. Hence, we decided to use initially an excess of the metal chlorides. The metalloporphyrins 2ad and 3ad (Scheme 1) have been obtained in yields exceeding 60%. No purification by column chromatography was required although in case of 2d, 3a and 3d the metalloporphyrins were re-precipitated for purification purposes (cf. Experimental section).

The purity of 2, 2a–d and 3, 3a–d was determined by CHN elemental analysis (EA), although this method has limits. For example, it is difficult to recognize by EA the presence of traces of impurities below ca. 0.5%. Furthermore, the measurement conditions of an EA may influence results as recently demonstrated for a series of octachlorometallophthalocyanines of the type MPcCl8 (MII = Cu, Ni, Co, Fe, Mn) [20]. However, for the herein reported porphyrins 2 and 3 and their corresponding metalloporphyrins 2ad and 3ad the CHN contents deviate by at most ±0.5%. Since 2/3 and 2ad/3ad are well soluble in solvents such as CH2Cl2, CHCl3, MeCN, DMSO, DMF it is possible to follow certain “criteria of purity” established by White, Bachmann and Burnham [21]. Thus, analytical amounts of these (metallo)porphyrins were chromatographed by thin layer chromatography (TLC) on alumina by using CHCl3/n-hexane mixtures (ratio 1:1, v/v) as eluent, showing that they were formed in high purity.

Furthermore, 1H NMR studies allowed us to monitor the progress of the metalation reactions of 2 and 3, even for the paramagnetic metalloporphyrins 2b,d and 3b,d. For example, the complete metalations of the free-base porphyrins 2 and 3 are indicated by the disappearance of their N–H 1H NMR resonances.

Electrospray ionization mass spectrometry

High-resolution mass spectrometry (HRMS) studies enable one to verify the successful formation of 2/3 and of 2ad/3ad. The ESIMS measurements in positive-ionization mode were performed under identical conditions, including the use of MeCN/CH2Cl2 solutions of the respective (metallo)porphyrin. The ESIMS spectra and the respective isotopic patterns of the ion peaks in form of [M]+, [M + H]+, [M + Na]+ or [M + K]+ agree to the calculated ones (cf. the ESIMS spectra in Supporting Information File 1). In agreement with Buchler [19] and Budzikiewicz [22] the mass spectrometric measurements served well to identify the type of the incorporated transition metal since the ion peaks of [M]+ and/or [M + H]+ are the ones with the highest intensity. The observation of [M + Na]+ as well as [M + K]+ ions and of cations of low m/z values, for example [393]+ (observed in the ESIMS spectra of 2c,d and 3c,d), is due to contaminants that typically appear in such measurements as described in the literature [23,24]. For 2b,c, 3 and 3ac double charged ion peaks are visible, clearly identifiable by an isotopic peak distance of m/z = 0.5. This is a common occurrence in ESI measurements when a higher concentration of the analyte is present [23].

IR studies

Severe difficulties were noticed when measuring KBr pellets of 2/3 and 2ad/3ad, as described by Alben [25]. These difficiculties are due to, for example, the optical inhomogeneity of the pellets. In order to avoid them, and as suggested by Alben [25], all (metallo)poprhyrins were intensively grinded to a fine flour before further grinding with KBr was done. It must be emphasized that due to the recommended intense and thus time-consuming grinding of the pure (polycrystalline) materials the IR spectra reveal the presence of water, likely due to the hygroscopic nature of the compounds and/or of KBr. In Figure 2 (2, 2ad) and Figure 3 (3, 3ad) the spectral region between 500 and 1800 cm−1 is displayed. Shaded areas within individual IR spectra displayed in Figure 2 and Figure 3 belong to related absorptions and are numbered. The wavenumbers of these absorptions are summarized in Table 1 for 2/2ad and 3/3ad. Full IR spectra (KBr) of 2/3 and of 2ad/3ad are given in Supporting Information File 1. Furthermore, Supporting Information File 1 shows the IR spectra of 2/3 and of 2ad/3ad as obtained by FTIR measurements with a Nicolet iS10 spectrometer (ATR attachment, ZnSe crystal) for comparison.

[2190-4286-8-121-2]

Figure 2: IR spectra (KBr) in the range of 500–1800 cm−1 for H2TPP(CONMe2)4 (2, top) and MTPP(CONMe2)4 (MII = Zn, 2a (gray); Cu, 2b (blue); Ni, 2c (orange); Co, 2d (purple)).

[2190-4286-8-121-3]

Figure 3: IR spectra (KBr) in the range of 500–1800 cm−1 for H2TPP(CON(iPr)2)4 (3, top) and MTPP(CON(iPr)2)4 (MII = Zn, 3a (gray); Cu, 3b (blue); Ni, 3c (orange); Co, 3d (purple)).

Table 1: Wavenumbers of numbered IR vibrations of 2/2ad and 3/3ad in the range from 500–1800 cm−1.a

no. H2 Zn Cu Ni Co
2 3 2a 3a 2b 3b 2c 3c 2d 3d
1 582 524 524 585 526 588 526 581 528
2 632 587 630 587 634 588 647 588 632 587
3 658 622 659 622 668 622 668 623 656 623
4 711 709 718 716 719 715 715 712 718 715
5 732 737
6 760 760 762 762 761 762 762 762 761 762
7 804 800 796 797 800 798 800 801 798 800
8 810 818 812 819 815 822 816 820 815
9 835 836 836 837 836
10 860 859 860 860 861 860 860 860 861 861
11 878 875 875 883 876 882 875
12 920 917 919 917 918 917 921 917 919 917
13 966 968
14 987 982 996 996 1000 1000 1003 1003 1002 1001
15 1021 994 1011 1016 1016 1017
16 1059 1019 1063 1021 1059 1055 1057
17 1084 1036 1086 1034 1083 1035 1083 1037 1082 1036
18 1063 1072
19 1073 1076 1030 1078 1134 1072
20 1096 1097 1095 1096 1096
21 1106 1105 1105 1106 1106
22 1137 1138 1138 1137 1138
23 1186 1160 1180 1156 1182 1158 1180 1161 1180 1160
24 1216 1190 1205 1181 1206 1190 1211 1183 1211 1186
25 1266 1212 1264 1206 1266 1209 1265 1209 1265 1209
26 1351 1340 1337 1339 1345 1340 1351 1340 1349 1339
27 1370 1370 1371 1370 1370
28 1378 1378 1378 1379 1379
29 1399 1395 1400 1390 1398 1391 1397 1393 1397 1392
30 1451 1442 1448 1443 1450 1441 1450 1441 1451 1440
31 1489 1473 1487 1472 1489 1472 1489 1472 1488 1473
32 1516 1508 1515 1507 1518 1506 1514 1507 1514 1508
33 1558 1561 1560 1556 1560
34 1609 1609 1612 1607 1608 1608 1619 1610 1609
35 1628 1630 1632 1622 1632 1626 1630 1625 1629
36 1732 1701 1730 1700 1711 1730 1710 1733 1699

acf. Figure 2 and Figure 3.

For the porphyrins 2 and 3 three different N–H vibrations at 3310–3326 cm−1, 975–990 cm−1 and 675–700 cm−1 are expected according to [25]. The one observed at 3317 cm−1 for both 2 and 3 (Supporting Information File 1) fits well into the expected range. The vibrations no. 5 and no. 13 for 2 (966 and 732 cm−1) and 3 (968 and 737 cm−1), cf. Figure 2 and Figure 3 and Table 1, are attributed to the other two N–H vibrations. They deviate to some extend from the expected ranges, see above, but the corresponding metalloporphyrins do not show related vibrations (Figure 2 and Figure 3).

The spectral range from 3000 to 2800 cm−1 is governed by νas(C–H) and νs(C–H) absorptions of the aliphatic substituents R of the –C(O)NR2 groups of both 2/2ad and 3/3ad (Supporting Information File 1). According to [26], CH3 groups can be identified by one νas(C–H) absorption at ca. 2950 cm−1 and up to two νs(C–H) absorptions at lower spatial frequencies of ca. 2800 cm−1. The number of CH3 groups is eight for 2/2ad, that of 3/3ad is 16. This difference is nicely reflected in the intensities and shapes of the νas(C–H) and νs(C–H) absorptions. Among 2/2ad only for 2a and 2c all three possible absorptions could be observed, while further members exhibit only one νs(C–H) and the νas(C–H) vibration (Supporting Information File 1). For 3/3ad the νas(C–H) vibration is always the most intensive one at 2970 ± 1 cm−1, followed by a less intensive first νs(C–H) absorption (2932 ± 1 cm−1) and a third even less intensive νs(C–H) band (2874 ± 4 cm−1). Due to these different spectral features it is possible to differentiate between a type 2/2ad or 3/3ad (metallo)porphyrin.

For the porphyrin cores and the aromatic C6H4 moieties, respectively, ν(C[Graphic 1]H) and ν(C=H) vibrations are expected above 3000 cm−1. However, these vibrations as well as combinations of γ(C[Graphic 2]H) vibrations between 2000 and 1600 cm−1, could not be identified unambiguously or were too weak. Likely, this is due to the substitution of the aromatic C6H4 rings, decreasing the intensities of these vibrations [26].

The presence of CH3 groups in a compound is indicated in the IR spectra in general by one δas(C–H) (ca. 1465 cm−1) vibration and at least one δs(C–H) (ca. 1380 cm−1) vibration [26]. Furthermore, a single δs(C–H) absorption verifies that the CH3 group belongs to an aliphatic chain that is not branched, or that the Me group is terminal as in the –NMe2 entities of 2/2ad. For branched alkyl chains the δs(C–H) vibration splits into two [26]. Thus, the absorptions no. 30 and no. 26 of 2/2ad (1450 ± 2 cm−1 and 1344 ± 7 cm−1) are attributed to the δas(C–H) and δs(C–H) vibrations of the terminal CH3 groups (Figure 2 and Table 1). Due to a larger number of CH3 groups in 3/3ad compared to 2/2ad the νas(C–H), νs(C–H), δas(C–H) and δs(C–H) absorptions of 3/3ad are more intensive compared to 2/2ad. For example, the absorption no. 30 of 3/3adas(C–H), 1442 ± 2 cm−1) is significantly more intensive compared to 2/2ad (Figure 2, Figure 3 and Table 1). As expected, for 3/3ad two δs(C–H) vibrations are observed, see no. 28 (1379 ± 1 cm−1) and no. 27 (1371 ± 1 cm−1) in Figure 3 and Table 1. The presence of iPr groups in 3/3ad was recognized further by their skeletal vibrations at 1158 ± 3 cm−1 (no. 23), shouldered at 1136 ± 2 cm−1 (no. 22) [21], while for 2/2ad only a weak absorption at 1183 ± 3 cm−1, denoted as no. 23, is observed.

For para-substituted C6H4 aromatic units one γ(C[Graphic 3]H) absorption between 800 and 860 cm−1 is expected [27], which is one of absorptions no. 7, 8 or 10 of 2/2ad and 3/3ad, (Figure 2, Figure 3 and Table 1). A more precise assignment is not possible, because C[Graphic 4]H vibrations of the β-pyrrolic hydrogens are expected to lead to absorptions at 772–805 cm−1 [27]. Further β-pyrrolic C[Graphic 5]H vibrations are expected at 1045–1065 cm−1 [13], and thus no. 17 of 2/2ad and 3/3ad can be assigned to them (Figure 2, Figure 3 and Table 1).

The two strongest absorptions of 2/2ad and 3/3ad are due to ν(C[Graphic 6]C) vibration of the aromatic moieties and ν(C=O) vibrations of the terminal –C(O)NR2 groups [27]. The ν(C[Graphic 7]C) vibrations are expected at ca. 1600 cm–1, while the more intense ν(C=O) are observed between 1650 and 1690 cm−1 [27]. This allows for an assignment of no. 35 and no. 34 (Figure 2, Figure 3 and Table 1) to the former and the latter type of vibration, respectively. However, 2/2ad always exhibit one broad absorption band at ca. 1620 cm−1, which hinders a more precise assignment. For 3/3a-d this situation is different and these two absorption bands occur well resolved. Most likely, that difference can be attributed to the different substitution of the terminal –C(O)NR2 groups.

UV–vis studies

The UV–vis absorption spectra of 2/2ad and 3/3ad were recorded in CHCl3 solution in the spectral range of 230–700 nm. In order to avoid possible impact of the concentrations on λabs and ε, which was reported for (metallo)phthalocyanines [28], we performed concentration-dependent UV–vis measurements. According to [28] the nature (cofacial, face-to-face, tilted) and degree (dimer, oligomer, polymer) of mutual interactions between (metallo)phthalocyanine molecules might modify their optical absorption spectra [28]. However, the UV–vis studies of 2/2ad and 3/3ad with varying concentrations revealed marginal impact on λabs (max. ±1 nm) and ε (max. ±4%), see Supporting Information File 1. Larger deviations of ε are attributed to random errors due to, for example, uncertainties in diluting the sample solutions. The UV–vis spectra of 2/2ad and 3/3ad displaying the absorption spectral range from 280–700 nm are shown in Figure 4. For better comparison we select the spectrum of an individual (metallo)porphyrin in which the maximum of the absorption is closest to 1.5 (Supporting Information File 1). Inserts in Figure 4 correspond to the enlarged spectral range of 480–700 nm. Optical absorptions are numbered in relation to the wavelength, λabs and log ε values are summarized in Table 2.

[2190-4286-8-121-4]

Figure 4: Left: UV–vis spectra (CHCl3, 280–700 nm) of H2TPP(C(O)NMe2)4 (2) and MTPP(C(O)NMe2)4 (MII = Zn, 2a (gray); Cu, 2b (blue); Ni, 2c (orange); Co, 2d (purple)). Right: UV–vis spectra (CHCl3, 280–700 nm) of H2TPP(C(O)N(iPr)2)4 (3) and MTPP(C(O)N(iPr)2)4 (MII = Zn, 3a (gray); Cu, 3b (blue); Ni, 3c (orange); Co, 3d (purple)).

Table 2: Wavelengths of UV–vis absorption bands of 2/2ad and 3/3ad in the range of 280–700 nm.a

compound absorption band no.
1 2 3 4 5 6 7 8
λabs (log ε)
2 401 (4.95) 420 (5.64) 449 (4.74) 516 (4.35) 551 (4.08) 591 (3.96) 647 (3.93) 666 (3.93)
3 400 (4.80) 421 (5.49) 517 (4.17) 552 (3.91) 590 (3.74) 648 (3.58)
2a 403 (4.55) 426 (5.55) 555 (4.19) 596 (3.73)
3a 404 (4.33) 426 (5.29) 556 (3.93) 597 (3.53)
2b 396 (4.44) 419 (5.65) 542 (4.28) 578 (3.39)
3b 397 (4.58) 419 (5.74) 542 (4.37) 579 (3.43)
2c 416 (5.30) 528 (4.17)
3c 417 (5.32) 530 (4.23)
2d 412 (5.24) 442 (4.44) 530 (4.03)
3d 412 (5.47) 529 (4.25)

acf. Figure 4

Generally, absorption spectra of free-base porphyrins consist of characteristic absorption bands: The more intense Soret band (or B band) arising from a1u(π)→eg*(π) transitions and two Q bands (Qx(0,0) and Qy(0,0) from a2u(π)→eg*(π) transitions [29,30]. According to Goutermann the B(0,0) band appears between 380 and 420 nm (ε > 105 M−1·cm−1) and is accompanied in case of well-resolved spectra by a blue-shifted (ca. 1250 cm−1) B(1,0) band [29,30]. Q-band absorptions occur in the spectral region between 500 and 700 nm (ε > 104 M−1·cm−1) [29,30]. The Qx(0,0) and Qy(0,0) bands of D2h-symmetric porphyrins, separated by ca. 3000 cm−1, might be observed inclusive a vibronic overtone absorption of each Q band, denoted as Qx(1,0) and Qy(1,0) [29,30]. For metalloporphyrins adapting D4h-type symmetry, the four Q bands are observed to collapse into two Q bands, in some cases into only one [19,29]. The accompanying “[…]Soret band may remain in the usual range or shifted to higher or lower frequency.[…]”, according to Buchler [19]. Furthermore, (metallo)porphyrins may show a weak N (ca. 325 nm) and M band (ca. 215 nm), often with an even weaker L band [29].

As expected, for 2 and 3 the intensive B(0,0) band appears at ca. 420 nm (no. 2 in Figure 4, Table 2) and is followed by four significantly weaker Q bands at ca. 516, 551, 591 and 647 nm (no. 4–7 in Figure 4, Table 2). The separation between absorption no. 4 and no. 6 as well as between no. 5 and no. 7 amounts to, respectively, 2394 cm−1 as well as 2684 cm−1 for 3, in good agreement with the expected difference between the Qx(0,0) and Qy(0,0) band of free-base porphyrins (see below). The blue-shifted shoulder of the B(0,0) band at 401/400 nm (no. 1 in Figure 4, Table 2) corresponds to the B(1,0) band of 2 and 3, confirmed by blue-shifts of 1128 and1247 cm−1 (see above). As described earlier, and due to symmetry reasons, for ZnII- and CuII-containing 2a/3a and 2b/3b, two Q bands are observed, while NiII- and CoII-containing 2c/3c and 2d/3d possess only one Q band (Figure 4). The difference in numbers of the Q bands could be caused by a higher molecular symmetry of 2c/3c or 2d/3d compared to 2a/3a and 2b/3b, but is most likely attributable to weak perturbations by the central metal according to Goutermann [29]. A comparison of the λabs values of both the B(0,0) and the Q band(s) along 2/2ad and 3/3ad reveals a red-shift along the series CoII < NiII < CuII < ZnII (Figure 4 and Table 2). This observation is in agreement with observations summarized by Buchler [19] and Goutermann [29]. The same tendency has been observed more recently [11] and no significant differences of λabs values have been noticed [12], although the UV–vis spectra were recorded in both cases in CHCl3.

Thermogravimetric studies

Part of our motivation to synthesize 2/2ad and 3/3ad originates from a number of cooperations with our partners in the DFG-supported research unit “Towards Molecular Spintronics” [6-9]. For example, (metallo)porphyrins were synthesized and deposited by OMBD for different kinds of physical thin-film studies [6-9]. In one of these contributions thin films of CuTPP(OMe)4 (Figure 1) were investigated by current-sensing atomic force microscopy [8]. It was concluded that for the investigation of films with different morphologies and transport properties further (metallo)porphyrins should be studied, as outlined in the Introduction section [6-9].

However, we were not able to deposit thin films of 3, 3b and 3d nor of 2, 2c and 2d by means of OMBD. In more detail: OMBD parameters were initially chosen as reported in [8]. Thus, at 2 × 10−7 mbar a deposition rate of 5 Å/min was adjusted. In all investigated cases, deposition rates were not stable and constantly decreased over time. In order to maintain a stable deposition rate, the deposition temperatures were constantly increased from 300 to 350 °C in a Knudsen cell. After keeping the materials for ca. 20 min at these high temperatures, it was observed that the deposition rates dropped significantly. From this point onwards, it was not possible to perform any (further) deposition of the materials. In case of 3b and 3d the remaining material in the Knudsen cell was subjected to IR measurements (Supporting Information File 1) in comparison with measurements of the starting materials, showing that both metalloporphyrins decomposed during the OMBD studies.

In order to shine more light into the temperature stability we carried out TG studies for 3, 3b, 3d, 2, 2c and 2d. The TG traces are shown in Figure 5 together with the one of H2TPP(OH)4. In our earlier studies [6,7], H2TPP(OH)4 could be deposited successfully by applying OMBD parameters analogous the those described above. A comparison especially of the onset temperatures of the decomposition processes reveals that H2TPP(OH)4 is obviously significantly more thermally stable than the here reported (metallo)porphyrins. Because of this, OMBD of 2/2ad and 3/3ad is not possible and we are recently fabricating thin layers of these compounds by spin-coating [31].

[2190-4286-8-121-5]

Figure 5: Top: TG traces of 3, 3b and 3d in comparison with H2TPP(OH)4. Bottom: TG traces of 2, 2c and 2d in comparison with H2TPP(OH)4.

Conclusion

Two series of metalloporphyrins MTPP(C(O)NR2)4 (M = CoII, NiII, CuII, ZnII) derived out of their free-base species H2TPP(C(O)NR2)4 (R = Me (2/2ad), iPr (3/3ad)) were synthesized and characterized by NMR, IR and UV–vis spectroscopy as well as by ESI mass-spectrometry. The comparison of the obtained analytical results revealed only minor differences in vibrational and optical spectra, both with respect to the varied transition metal ions as well as the terminal organic substituent R. That provides potentially useful insight into the material properties of these porphyrins. It was anticipated that the variation of the central transition metal ions along 2ad and 3ad modify to the local transport characteristics of OMBD-deposited thin films of these compounds. In addition, in order to modify thin-film morphologies of successfully OMBD-deposited CuTPP(OMe)4 2/2ad and 3/3ad were equipped with sterically more bulky terminal organic groups. Unfortunately, all trials to deposit members of 2/2ad and 3/3ad by OMBD failed, which is attributed to a significantly lower thermal stability compared to CuTPP(OMe)4 [8]. Most likely, the decreased thermal stability of 2/2ad and 3/3ad can be attributed to fragmentations of the terminal –C(O)NR2 functionalities during heating. Thus, this study shows that the thermal stability of (metallo)porphyrins is subjected to certain limits, and the application of other thin-film depositions techniques is required for 2/2a–d and 3/3a–d.

Experimental

General conditions

All chemicals were purchased from commercial sources and were used as received, unless stated otherwise. All reactions were carried out under argon atmosphere using standard Schlenk techniques and vacuum-line manipulations unless stated otherwise. All solvents were distilled prior to use and were purified/dried according to standard procedures [32].

Starting materials

5,10,15,20-Tetra(4-carboxyphenyl)porphyrin (H2TPP(COOH)4, 1) was synthesized according to [33] and MCl2·nH2O salts (M = ZnII, CuII, NiII, CoII) were dried according to [34].

Instruments

NMR spectra were recorded at ambient temperature with a Bruker Avance III 500 Ultra Shield Spectrometer (1H at 500.300 MHz and 13C{1H} at 125.813 MHz) in the Fourier transform mode. Chemical shifts are reported in δ (ppm) versus SiMe4 with the solvent as the reference signal CDCl3: 1H NMR, δ = 7.26; and 13C{1H} NMR, δ = 77.16. FTIR spectra were recorded in the range of 400–4000 cm−1 with a Perkin-Elmer 1000 FTIR spectrometer as KBr pellets and in the range of 650–4000 cm−1 with a Thermo Scientific Smart iTR, Nicolet iS10. (The two absorptions at ca. 2360 cm−1, which appear different in intensity from spectra to spectra, are due to CO2.) C, H, N elemental analyses were performed using a Thermo FlashAE 1112 series analyzer. High-resolution mass spectra were recorded with a Bruker micrOTOF QII equipped with an Apollo II ESI source. UV–vis absorption spectra were recorded with a Spectronic GENESYS 6 UV–visible spectrophotometer (Thermo Electron Corporation) between 200–800 nm. TG experiments were performed using a Mettler Toledo TGA/DSC1 1600 system with an MX1 balance.

Synthesis of 2

To a suspension of 1 (1.00 g, 1.26 mmol) in dichloromethane (140 mL) dimethylformamide (1 mL, 12.9 mmol) was added. This reaction mixture was cooled to 0 °C and oxalyl chloride (3.20 mL, 37.31 mmol) was added dropwise (within 20 min) under continuous stirring. The mixture was stirred at 0 °C for further 30 min followed by refluxing for 3 h. After all volatiles were removed under reduced pressure the obtained crude product was dissolved in dichloromethane (30 mL) and a mixture of dimethylamine (2 M in tetrahydrofuran, 16 mL, 32 mmol) and triethylamine (1 mL, 7.17 mmol) was added dropwise at ambient temperature. The reaction mixture was stirred at this temperature for another 3 h, followed by refluxing for 24 h. Afterward, all volatiles were removed under reduced pressure and hot distilled water (100 mL) was added to the crude product with continuous stirring for 30 min. The purple precipitate formed was filtered off, washed with hot distilled water (5 × 20 mL) and dried at 110 °C in an oven. Yield: 0.91 g (80% based on 1). Anal. calcd for C56H50N8O4 (899.05): C, 74.81; H, 5.61; N, 12.46; found: C, 74.3; H, 5.7; N, 12.2; 1H NMR (CDCl3) δ −2.80 (s, 2H, Ha,a′), 3.32 (s, 24H, H1,2), 7.84 (d, 8H, H6,6′), 8.26 (d, 8H, H5,5′), 8.87 (s, 8H, H10,10′); 13C{1H} NMR (CDCl3) δ 35.80 (C1), 40.15 (C2), 119.62 (C8), 125.80 (C6,6′), 134.57 (C7), 135.93 (C5,5′), 143.46 (C4), 171.80 (C3); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 899.4058 [2 + H]+, 937.3515 [2 + K]+; calcd for C56H51N8O4/C56H50KN8O4 ([2 + H]/[2 + K]) = 899.4028/937.3587; IR (KBr, cm−1) ν: 3317 (w, N–H); 2929/2897/2866 (m/w/w, C–H); 1629/1609 (s/w, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 401 (5.24), 420 (5.95), 449 (4.83), 516 (4.64), 551 (4.36), 591 (3.24), 647 (4.17), 666 (4.07); Supporting Information File 1 gives the IR, 1H NMR, 13C{1H} NMR, UV–vis and ESIMS spectra of 2.

Comments: According to Jones and Wilkins [35] for the –NMe2 groups two 13C NMR chemical shifts are observed. According to Manke et al. [36] the 13C NMR resonances of the pyrrole carbon atoms C9,9′ and C10,10′ are not observable.

Synthesis of 3

To a suspension of 1 (1.00 g, 1.26 mmol) in dichloromethane (140 mL), dimethylformamide (1 mL, 12.9 mmol) was added. This reaction mixture was cooled to 0 °C and oxalyl chloride (3.20 mL, 37.31 mmol) was added dropwise (within 20 min) under continuous stirring. The mixture was stirred at 0 °C for further 30 min followed by refluxing for 3 h. After all volatiles were removed under reduced pressure the obtained crude product was dissolved in dichloromethane (30 mL), and a mixture of diisopropylamine (11.52 g, 0.114 mol, 16 mL) and triethylamine (1 mL, 7.17 mmol) was added dropwise at ambient temperature. The reaction mixture was refluxed for 24 h. After cooling to ambient temperature, all volatiles were removed under reduced pressure, and hot distilled water (100 mL) was added to the crude product under continuous stirring for 30 min. The purple precipitate formed was filtered off, washed with hot distilled water (5 × 20 mL) and dried at 110 °C. Yield: 1.21 g (85% based on 1). Anal. calcd for C72H82N8O4 (1123.47): C, 76.97; H, 7.36; N, 9.97; found: C, 76.8; H, 7.2; N 9.9. 1H NMR (CDCl3) δ −2.78 (s, 2H, Ha,a′), 1.43/1.66 (s(broad)/s(broad), 24H/24H, H1,1′,2,2′), 3.71/4.31 (s(broad)/s(broad), 4H/4H, H3,3′), 7.74 (d, 8H, H7,7′), 8.24 (d, 8H, H6,6′), 8.90 (s, 8H, H11,11′); 13C{1H} NMR (CDCl3) δ 21.24 (C1,1′,2,2′), 119.8 (C9), 124.6 (C7,7′), 134.8 (C8), 138.6 (C6,6′), 142.8 (C5), 171.3 (C4); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 1123.6520 [3 + H]+, 1145.6319 [3 + Na]+; calcd for C72H83N8O4/C72H82NaN8O4 ([3 + H]/[3 + Na]) = 1123.6532/1145.6351; IR (KBr, cm−1) ν: 3317 (w, N–H); 2969/2932/2874 (m/w/w, C–H); 1630/1608 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 400 (4.80), 420 (5.49), 482 (3.74), 517 (4.17), 552 (3.91), 591 (3.74), 648 (3.58). Supporting Information File 1 gives the IR, 1H NMR, 13C{1H} NMR, UV–vis and ESIMS spectra of 3.

Comments: The 1H NMR resonances of the N(iPr)2 groups are all broadened. The hydrogen atoms H1,1′,2,2′ are regarded to correspond to the two broad singlets at 1.39 and 1.69 ppm. The hydrogen atoms H3,3′ are regarded to correspond to the two singlets at 3.71 and 4.31 ppm. Both assignments could, however, not be verified by additional 2D NMR experiments (1H,1H-COSY,1H,13C-HSQCETGP and HMBCGP) because of too broad NMR resonances and/or the comparatively poor solubility. According to Jones and Wilkins [35] for the –NMe2 groups two 13C NMR chemical shifts are observed. According to Manke et al. [36] the 13C NMR resonances of the pyrrole carbon atoms C9,9′ and C10,10′ are not observable.

General procedure for the synthesis of 2a–d and 3a–d

Unless stated otherwise, the following procedure was used: To a solution of 2 (0.200 g, 0.222 mmol) for 2ad, or 3 (0.200 g, 0.178 mmol) for 3ad in dimethylformamide (25 mL), a solution of the MCl2 salt (3 equiv) in dimethylformamide (5 mL) was added dropwise (within 5 min) at ambient temperature. The reaction temperature was raised to 140 °C for 6 h. After cooling the reaction mixture to ambient temperature, chloroform (50 mL) was added and the combined organic phases were washed with water (3 × 40 mL) and brine (3 × 40 mL) to remove the excess of the MCl2 salt. The organic phase was dried over magnesium sulfate, and all volatiles were removed in vacuo to afford solids of the corresponding metalloporphyrins, which were dried additionally in vacuo for 12 h. Afterward, the corresponding solids were dissolved in CHCl3 and precipitated with n-hexane. That procedure is referred to in the following as “re-precipitation”.

Data for 2a

2 (0.200 g, 0.222 mmol), ZnCl2 (0.0909 g, 0.667 mmol). Yield: 0.156 g (73% based on 2); purple solid. Anal. calcd for C56H48N8O4Zn (962.44): C, 69.88; H, 5.03; N, 11.64; found: C, 69.5; H, 5.0; N, 11.5; 1H NMR (CDCl3) δ 3.16/3.26 (s/s, 12H/12H, H1,2), 7.68 (d, 8H, H6,6′), 8.23 (d, 8H, H5,5′), 8.93 (s, 8H, H10,10′); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 960.3058/961.3149 [2a]+/[2a + H]+, 983.2908 [2a + Na]+, 999.2716 [2a + K]+; calcd for C56H48N8O4Zn/C56H49N8O4Zn, C56H48NaN8O4Zn, C56H48KN8O4Zn ([2a]/[2a + H], [2a + Na], [2a + K] = 960.3058/961.3163, 983.2982, 999.2722; IR (KBr, cm−1) ν: 2929 (w, C–H); 1612 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 403 (4.55), 426 (5.55), 555 (4.19), 596 (3.73). Supporting Information File 1 gives the IR, 1H NMR, UV–vis and ESIMS spectra of 2a.

Comments: No re-precipitation needed. Due to the poor solubility of 2a a 13C NMR spectrum could not be recorded. The ESIMS spectra of 2a reveals as basis peak 988.3599. The origin of this peak remains unclear and may likely correspond to a fragmentation/recombination process under ESIMS measurement conditions.

Data for 2b

2 (0.200 g, 0.222 mmol), CuCl2 (0.0897 g, 0.667 mmol). Yield: 0.130 g (61% based on 2); wine red solid. Anal. calcd for C56H48CuN8O4 (960.58): C, 70.02; H, 5.04; N, 11.76; found: C, 69.9; H, 5.0; N, 11.6; HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 960.3254 [2b]+; calcd for C56H48CuN8O4 [2b] 960.3128; IR (KBr, cm−1) ν: 2928/2932 (w/w, C–H); 1622 (C=O); UV–vis (CHCl3) λabs [nm] (log ε): 396 (4.44), 419 (5.65), 543 (4.28), 578 (3.39). Supporting Information File 1 gives the IR, UV–vis and ESIMS spectra of 2b.

Comments: No re-precipitation needed.

Data for 2c

2 (0.200 g, 0.222 mmol), NiCl2 (0.0865 g, 0.667 mmol). Yield: 0.149 g (70% based on 2); brown solid. Anal. calcd for C56H48N8NiO4 (955.72): C, 70.38; H, 5.06; N, 11.72; found: C, 70.1; H, 5.0; N, 11.6; 1H NMR (CDCl3) δ 3.27 (s, 24H, H1,2), 7.76 (d, 8H, H6,6′), 8.05 (d, 8H, H5,5′), 8.76 (s, 8H, H10,10′); 13C{1H} NMR (CDCl3) δ 24.41 (C1), 33.87 (C2), 118.47 (C8), 125.96 (C6,6′), 132.46 (C10,10′), 133.73 (C7), 135.96 (C5,5′), 142.20 (C9,9′), 142.67 (C4), 171.69 (C3); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 955.3153 [2c + H]+; calcd for C56H49N8NiO4 [2c + H] = 955.3225; IR (KBr, cm−1) ν: 2924/2854 (w/w, C–H); 1626 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 416 (5.30), 528 (4.17). Supporting Information File 1 gives the IR, 1H NMR, 13C{1H} NMR, UV–vis and ESIMS spectra of 2c.

Comments: No re-precipitation needed. Due to a better solubility of 2c as compared to 2a, 13C NMR spectra could be recorded. In contrast to comments made for 2, all chemically different carbon atoms were observable, although for the –NMe2 groups of 2c two 13C NMR resonances were observed as reported for 2.

Data for 2d

2 (0.200 g, 0.222 mmol), CoCl2 (0.0867 g, 0.667 mmol). Yield: 0.155 g (73%, based on 2); wine red solid. Anal. calcd for C56H48CoN8O4 (955.96): C, 70.36; H, 5.05; N, 11.72; found: C, 70.1; H, 5.0;N, 11.7; HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 955.3125 [2d]+; calcd for C56H48N8CoO4 [2d] = 955.3125; IR (KBr, cm−1) ν: 2927/2852 (w/w, C–H); 1625 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 412 (5.24), 442 (4.44), 530 (4.03). Supporting Information File 1 gives the IR, UV–vis and ESIMS spectra of 2d.

Comments: Re-precipitation needed.

Data for 3a

3 (0.200 g, 0.178 mmol), ZnCl2 (0.0728 g, 0.534 mmol). Yield: 0.192 g (91% based on 3); purple solid. Anal. calcd for C72H80N8O4Zn (1186.87): C, 72.86; H, 6.79; N, 9.44, found: C, 72.1; H, 6.6; N, 9.23; 1HNMR (CDCl3) δ 1.45/1.59 (s(broad)/s(broad), 24H/24H, H1,1′,2,2′), 3.68/4.31 (s(broad)/s(broad), 4H/4H, H3,3′), 7.65 (d, 8H, H7,7′), 8.22 (d, 8H, H6,6′), 8.98 (s, 8H, H11,11′); 13C{1H} NMR (CDCl3) δ 20.85 (C1,1′,2,2′), 120.46 (C9), 124.11 (C7,7′), 132.08 (C11,11′), 134.48 (C8), 137.85 (C6,6′), 143.34 (C5), 150.08 (C10,10′), 171.08 (C4); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 1185.5632 [3a + H]+, 1207.5471 [3a + Na]+; calcd for C72H81ZnN8O4/C72H80NaZnN8O4 ([3a + H]/[3a + Na]) = 1185.5667/1207.5486; IR (KBr, cm−1) ν: 2969/2928/2869 (m/w/w, C–H); 1632 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 404 (4.33), 426 (5.29), 556 (3.93), 597 (3.53). Supporting Information File 1 gives the IR, 1H NMR, 13C{1H} NMR, UV–vis and ESIMS spectra of 3a.

Comments: Re-precipitation needed. Because 3a is better soluble than 2a, 13C NMR spectra could be recorded. In contrast to comments made for 3, all chemically different carbon atoms beside C3,3′ (belonging to the –N(iPr)2 groups) were observable. On the other hand, as discussed for 3 broad singlets in the 1H NMR spectra are regarded to correspond to the hydrogen atoms H1,1′,2,2′,3,3′.

Data for 3b

3 (0.200 g, 0.178 mmol), CuCl2 (0.0718, 0.534 mmol). Yield: 0.124 g (59% based on 3); wine red solid. Anal. calcd for C72H80CuN8O4(1185.0): C, 72.98; H, 6.80; N, 9.46; found: C, 72.5; H, 6.7;N, 9.4; HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 1184.5665 [3b]+; calcd for C72H80CuN8O4 [3b] = 1184.5671; IR (KBr, cm−1) ν: 2966/2928/2869 (m/w/w, C–H); 1632 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 397 (4.58), 419 (5.72), 542 (4.36), 579 (3.46). Supporting Information File 1 gives the IR, UV–vis and ESIMS spectra of 3b.

Comments: No re-precipitation needed.

Data for 3c

3 (0.200 g, 0.178 mmol), NiCl2 (0.0692 g, 0.534 mmol). Yield: 0.126 g (60%, based on 3); brown solid. Anal. calcd for C72H80N8NiO4(1180.15): C, 73.28; H, 6.83; N, 9.49; found: C, 72.9; H, 6.8; N, 9.4; 1H NMR (CDCl3) δ 1.40/1.62 (s(broad)/s(broad), 24H/24H, H1,1′,2,2′), 3.70/4.23 (s(broad)/s(broad), 4H/4H, H3,3′), 7.66 (d, 8H, H7,7′), 8.03 (d, 8H, H6,6′), 8.79 (s, 8H, H11,11′); 13C{1H} NMR (CDCl3) δ 21.00 (C1,1′,2,2′), 118.55 (C9), 124.65 (C7,7′), 132.46 (C11,11′), 133.96 (C8), 138.57 (C6,6′), 141.34 (C5), 142.76 (C10,10′), 171.07 (C4); HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 1179.5713 [3c + H]+, 1201.5520 [3c + Na]+; calcd for C72H81NiN8O4/C72H80NaNiN8O4 ([3c + H]/[3c + Na]) = 1179.5729/1201.5548; IR (KBr, cm−1) ν: 2969/2928/2875 (w/w/w, C–H); 1630 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 417 (5.32), 530 (4.23). Supporting Information File 1 gives the IR, 1H NMR, 13C{1H} NMR, UV–vis and ESIMS spectra of 3c.

Comments: No re-precipitation needed. As discussed for 3a (above), analogous observations were made for 3c.

Data for 3d

3 (0.200 g, 0.178 mmol), CoCl2 (0.0693 g, 0.534 mmol). Yield: 0.164 g (78%, based on 3); wine red solid. Anal. calcd for C72H80CoN8O4 (1180.39): C, 73.26; H, 6.83; N, 9.49; found: C, 72.8; H, 6.7; N, 9.3; HRMS (ESI-TOF, positive mode, MeCN/CH2Cl2): m/z 1179.5561 [3d]+; calcd for C72H80CuN8O4 [3d] = 1179.5629; IR (KBr, cm−1) ν: 2963/2931/2869 (m/w/w, C–H); 1629 (s, C=O); UV–vis (CHCl3) λabs [nm] (log ε): 412 (5.47), 529 (4.25). Supporting Information File 1 gives the IR, UV–vis and ESIMS spectra of 3d.

Comments: Re-precipitation needed.

Supporting Information

Supporting Information File 1 features 1H and 13C{1H} NMR spectra of 2, 2a, 2c, 3, 3a and 3c, ESIMS, UV–vis and IR spectra (ATR-IR and KBr) of 2, 2a2d, 3 and 3a3d, and IR spectra of 3b and 3d before and after OMBD together with optical photographs of the materials.

Supporting Information File 1: Additional experimental data.
Format: PDF Size: 4.0 MB Download

Acknowledgements

This work has been supported by the Deutsche Forschungsgemeinschaft through project FOR 1154 “Towards Molecular Spintronics”. We thank Janine Freytag, Brigitte Kempe and Dipl.-Chem. Natalia Rüffer for EA, ESIMS and TG measurements.

References

  1. Dolphin, D. The Porphyrins; Academic Press: New York, NY, USA, 1978.
    Return to citation in text: [1] [2]
  2. Kadish, K. M.; Smith, K. M.; Guiard, R. The Porphyrins Handbook; Academic Press (Elsevier Science): Amsterdam, Netherlands, 2000.
    Return to citation in text: [1] [2]
  3. Vicente, M. G. H.; Smith, K. M. Curr. Org. Synth. 2014, 11, 3–28. doi:10.2174/15701794113106660083
    Return to citation in text: [1] [2]
  4. Birnbaum, T.; Hahn, T.; Martin, C.; Kortus, J.; Fronk, M.; Lungwitz, F.; Zahn, D. R. T.; Salvan, G. J. Phys.: Condens. Matter 2014, 26, 104201. doi:10.1088/0953-8984/26/10/104201
    Return to citation in text: [1] [2] [3] [4]
  5. Wang, F. J.; Yang, C. G.; Vardeny, Z. V. Phys. Rev. B 2007, 75, 245324. doi:10.1103/PhysRevB.75.245324
    Return to citation in text: [1]
  6. Smykalla, L.; Shukrynau, P.; Mende, C.; Rüffer, T.; Lang, H.; Hietschold, M. Surf. Sci. 2014, 628, 92–97. doi:10.1016/j.susc.2014.05.015
    Return to citation in text: [1] [2] [3] [4] [5] [6]
  7. Smykalla, L.; Shukrynau, P.; Mende, C.; Rüffer, T.; Lang, H.; Hietschold, M. Surf. Sci. 2014, 628, 132–140. doi:10.1016/j.susc.2014.06.001
    Return to citation in text: [1] [2] [3] [4] [5] [6]
  8. Siles, P. F.; Bufon, C. C. B.; Grimm, D.; Jalil, A. R.; Mende, C.; Lungwitz, F.; Salvan, G.; Zahn, D. R. T.; Lang, H.; Schmidt, O. G. Org. Electron. 2014, 15, 1432–1439. doi:10.1016/j.orgel.2014.04.004
    Return to citation in text: [1] [2] [3] [4] [5] [6] [7] [8] [9]
  9. Lungwitz, F.; Mende, C.; Fronk, M.; Haidu, F.; Lang, H.; Salvan, G.; Zahn, D. R. T. Thin Solid Films 2014, 571, 377–383. doi:10.1016/j.tsf.2014.03.055
    Return to citation in text: [1] [2] [3] [4] [5]
  10. Granados-Oliveros, G.; Páez-Mozo, E. A.; Ortega, F. M.; Piccinato, M. T.; Silva, F. N.; Guedes, C. L. B.; Di Mauro, E.; da Costa, M. F.; Ota, A. T. J. Mol. Catal. A: Chem. 2011, 339, 79–85. doi:10.1016/j.molcata.2011.02.015
    Return to citation in text: [1]
  11. Wang, C.; Yang, G.-M.; Li, J.; Mele, G.; Słota, G.; Broda, M. A.; Duan, M.-Y.; Vasapollo, G.; Zhang, X.; Zhang, F.-X. Dyes Pigm. 2009, 80, 321–328. doi:10.1016/j.dyepig.2008.08.008
    Return to citation in text: [1] [2]
  12. Zheng, W.; Shan, N.; Yu, L.; Wang, X. Dyes Pigm. 2008, 77, 153–157. doi:10.1016/j.dyepig.2007.04.007
    Return to citation in text: [1] [2]
  13. McGill, S.; Nesterov, V. N.; Gould, S. L. Acta Crystallogr., Sect. E 2013, 69, m471. doi:10.1107/S1600536813019338
    Return to citation in text: [1] [2] [3]
  14. Goldberg, I.; Krupitsky, H.; Stein, Z.; Hsiou, Y.; Strouse, C. E. Supramol. Chem. 1994, 4, 203–221. doi:10.1080/10610279408029473
    Return to citation in text: [1]
  15. Isthaiwi, Z.; Rüffer, T.; Klaib, S.; Buschbeck, R.; Walfort, B.; Lang, H. Dalton Trans. 2014, 43, 7868–7888. doi:10.1039/C3DT53535E
    Return to citation in text: [1]
  16. Chen, W.; El-Khouly, M. E.; Fukuzumi, S. Inorg. Chem. 2011, 50, 671–678. doi:10.1021/ic102208y
    Return to citation in text: [1] [2]
  17. Shirakawa, M.; Kawano, S. I.; Fujita, N.; Sada, K.; Shinkai, S. J. Org. Chem. 2003, 68, 5037–5044. doi:10.1021/jo0341822
    Return to citation in text: [1]
  18. Gradl, S. N.; Felix, J. P.; Isacoff, E. Y.; Garcia, M. L.; Trauner, D. J. Am. Chem. Soc. 2003, 125, 12668–12669. doi:10.1021/ja036155z
    Return to citation in text: [1] [2]
  19. Buchler, J. W. Synthesis and Properties of Metalloporphyrins. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, NY, USA, 1978; Vol. 1, pp 389–483. doi:10.1016/B978-0-12-220101-1.50017-2
    Return to citation in text: [1] [2] [3] [4] [5] [6] [7]
  20. Rüffer, T.; Nurpeisova, D.; Jakupova, Z.; Tashenov, A.; Uhlig, N.; Khalladi, A.; Mertens, L.; Gonser, A.; Mehring, M.; Lang, H. Z. Naturforsch., B 2017, submitted.
    Return to citation in text: [1]
  21. White, W. I.; Bachmann, R. C.; Burnham, B. F. Chromatography of porphyrins and metalloporphyrins. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, USA, 1978; Vol. I, pp 553–580. doi:10.1016/b978-0-12-220101-1.50019-6
    Return to citation in text: [1] [2]
  22. Budzikiewicz, H. Mass spectra of porphyrins and related compounds. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, NY, USA, 1978; Vol. 3, pp 395–461. doi:10.1016/B978-0-12-220103-5.50016-7
    Return to citation in text: [1]
  23. Cole, R. B. Electrospray ionization mass spectrometry: fundamentals, instrumentation, and applications; John Wiley & Sons, Inc.: New York, NY, USA, 1997.
    Return to citation in text: [1] [2]
  24. Keller, B. O.; Sui, J.; Young, A. B.; Whittal, R. M. Anal. Chim. Acta 2008, 627, 71–81. doi:10.1016/j.aca.2008.04.043
    Return to citation in text: [1]
  25. Alben, J. O. Infrared Spectroscopy of Porphyrins. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, NY, USA, 1978; Vol. 3, pp 323–345. doi:10.1016/B978-0-12-220103-5.50014-3
    Return to citation in text: [1] [2] [3]
  26. Steger, E.; Adler, B.; Brunn, J.; Doerffel, K.; Höbold, W.; Mehlhorn, A.; Müller, E.; Treibmann, D. Lehrwerkreihe Chemie: Strukturaufklärung- Spektroskopie und Röntgenbeugung, Arbeitsbuch; VEB Deutscher Verlag für Grundstoffindustrie: Leipzig, GDR, 1973.
    Return to citation in text: [1] [2] [3] [4]
  27. Becker, H. G. O.; Domschke, G.; Fanghänel, E.; Fischer, M.; Gewald, K.; Mayer, R.; Pavel, D.; Schmidt, H.; Schwetlick, K.; Berger, W.; Faust, J.; Gentz, F.; Gluch, R.; Müller, K.; Schollberg, K.; Seiler, E.; Zeppenfeld, G.; Fabian, J.; Frach, K.; Lohs, K.; Kläsz, V. Organikum; Deutscher Verlag der Wissenschaften: Berlin, GDR, 1976.
    Return to citation in text: [1] [2] [3] [4]
  28. McKeown, N. B. Phthalocyanine Materials Synthesis, Structure and Function; Cambridge University Press: UK, 1998; pp 88–93.
    Return to citation in text: [1] [2] [3]
  29. Gouterman, M. Optical Spectra and Electronic Structure of Porphyrins and Related Rings. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, NY, USA, 1978; Vol. 3, pp 2–24. doi:10.1016/B978-0-12-220103-5.50008-8
    Return to citation in text: [1] [2] [3] [4] [5] [6] [7] [8]
  30. Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138–163. doi:10.1016/0022-2852(61)90236-3
    Return to citation in text: [1] [2] [3] [4]
  31. Abdulmalic, M. A.; Fronk, M.; Bräuer, B.; Zahn, D. R. T.; Salvan, G.; Meva, F. E.; Rüffer, T. J. Magn. Magn. Mater. 2016, 419, 17–28. doi:10.1016/j.jmmm.2016.06.002
    Return to citation in text: [1]
  32. Perin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon: New York, NY, USA, 1988.
    Return to citation in text: [1]
  33. Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour, J.; Korsakoff, L. A. J. Org. Chem. 1967, 32, 476. doi:10.1021/jo01288a053
    Return to citation in text: [1]
  34. Freeman, J. H.; Smith, M. L. J. Inorg. Nucl. Chem. 1958, 7, 224–227. doi:10.1016/0022-1902(58)80073-1
    Return to citation in text: [1]
  35. Jones, R. G.; Wilkins, J. M. Org. Magn. Reson. 1978, 11, 20–26. doi:10.1002/mrc.1270110106
    Return to citation in text: [1] [2]
  36. Manke, A.-M.; Geisel, K.; Fetzer, A.; Kurz, P. Phys. Chem. Chem. Phys. 2014, 16, 12029–12042. doi:10.1039/c3cp55023k
    Return to citation in text: [1] [2]

Article is part of the series

Georgeta Salvan and Dietrich R. T. Zahn

Interesting articles

Pavel L. Padnya, Irina A. Khripunova, Olga A. Mostovaya, Timur A. Mukhametzyanov, Vladimir G. Evtugyn, Vyacheslav V. Vorobev, Yuri N. Osin and Ivan I. Stoikov

Zahra Shariatinia, Ebadullah Asadi, Vahid Tavasolinasab and Khodayar Gholivand

Matthias Bieligmeyer, Franjo Artukovic, Stephan Nussberger, Thomas Hirth, Thomas Schiestel and Michaela Müller

News

Logo OA

The 2016 Journal Impact Factor is 3.1 and the journal remained a Q1 applied physics and materials science journal.

Logo OA

Thematic Series currently open for submission: (1) Energy/nanoremediation (2) Light–Matter interactions (3) Topological materials (4) SPM for energy

Logo OA

A step forward for best Open Science practices.

© 2017 Al-Shewiki et al.; licensee Beilstein-Institut.
This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The license is subject to the Beilstein Journal of Nanotechnology terms and conditions: (http://www.beilstein-journals.org/bjnano)

 
Back to Article List