Allostreptopyrroles A–E, β-alkylpyrrole derivatives from an actinomycete Allostreptomyces sp. RD068384

• Marwa Elsbaey,
• Naoya Oku,
• Mohamed S. A. Abdel-Mottaleb and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2024, 20, 1981–1987, doi:10.3762/bjoc.20.174

• CHCl3/MeOH 10:1 fraction contained compounds with characteristic UV absorption. This fraction, obtained as 395 mg of brown solid from 4 L culture in A-3M medium, was fractionated by octadecyldimethylsilyl (ODS) silica gel column chromatography with a gradient of MeCN/0.1% HCO2H solution (2:8, 3:7, 4:6

Radical reactivity of antiaromatic Ni(II) norcorroles with azo radical initiators

• Siham Asyiqin Shafie,
• Ryo Nozawa,
• Hideaki Takano and
• Hiroshi Shinokubo

Beilstein J. Org. Chem. 2024, 20, 1967–1972, doi:10.3762/bjoc.20.172

• benzoyl peroxide, TEMPO, and the combination of alkyl halides with BEt3, were not applicable to this reaction. Physical properties The electronic absorption spectra of norcorrole 1 and adduct 2a are shown in Figure 3. While norcorrole 1 exhibited a weak absorption band from 600 nm to the NIR region, due

• to the characteristic forbidden HOMO–LUMO transition of the antiaromatic compound, nonconjugated macrocycle 2a did not possess such an absorption band, indicating the loss of antiaromaticity in 2a. Macrocycle 2a possessed new absorption bands from 600 to 800 nm. The simulated absorption spectrum of

• 2a obtained by TD DFT calculations at the M06/6-31G(d)+SDD//B3LYP-D3/6-31G(d)+SDD level of theory was consistent with the experimental results. Therein, the absorption band at 670 nm (f = 0.0026) was attributed to the transition from HOMO to LUMO+1. Next, the electrochemical properties of 2a in

A new platform for the synthesis of diketopyrrolopyrrole derivatives via nucleophilic aromatic substitution reactions

• Vitor A. S. Almodovar and
• Augusto C. Tomé

Beilstein J. Org. Chem. 2024, 20, 1933–1939, doi:10.3762/bjoc.20.169

• aromatic substitution; phenol; thiol; Introduction Diketopyrrolopyrroles (DPPs) are a class of organic pigments discovered by serendipity in the 1970s [1][2]. Generally, N-unsubstituted DPP derivatives exhibit high melting points, low solubility in most solvents, and strong absorption in the visible

• Micromass Q-TOF-2TM mass spectrometer and CHCl3 as the solvent. The NMR, absorption and emission spectra of the new compounds are shown in Supporting Information File 1. Synthesis 3,6-Bis(4-chlorophenyl)-2,5-bis(pentafluorobenzyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (2) A suspension of DPP 1 (1 g

• ), −144.36 to −144.49 (m, 2F), −149.67 (t, J = 20.8 Hz, 1F), −157.53 to −157.84 (m, 2F); ESIMS m/z: 792.1 (M + H+, 100%). (A) Absorption and (B) fluorescence spectra of compounds 3a–f, 4a, 4d and 4f, in DMF. Different concentrations of the compounds were used to allow visualization of each spectrum

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

A facile three-component route to powerful 5-aryldeazaalloxazine photocatalysts

• Ivana Weisheitelová,
• Radek Cibulka,
• Marek Sikorski and
• Tetiana Pavlovska

Beilstein J. Org. Chem. 2024, 20, 1831–1838, doi:10.3762/bjoc.20.161

• ]quinoline-2,4(1H,3H)-dione cyclic system. The absorption spectra of the methoxy derivatives 2f, 2j and 2n in DMF provide interesting information on the effect of the position of the methoxy group in the core of deazaalloxazine on the absorption maxima (Figure 2). The 8-methoxydeazaalloxazine 2n exhibited a

• /alloxazine photoredox catalysis [9][14][15][16][17][18][19], 7-methoxyderivatives should also be considered due to their absorption closer to the visible light region. This allows longer wavelength LEDs with lower energy photons to be applied, potentially contributing to avoiding undesired reactions [14][15

• potent, biologically active compounds. Interestingly, the introduction of a strong methoxy group at position 7 of the 5-aryldeazaalloxazine core led to a bathochromic shift in the absorption spectra of the synthesised molecules, making them more suitable for visible light photocatalysis. Experimental

Synthesis and characterization of 1,2,3,4-naphthalene and anthracene diimides

• Adam D. Bass,
• Daniela Castellanos,
• Xavier A. Calicdan and
• Dennis D. Cao

Beilstein J. Org. Chem. 2024, 20, 1767–1772, doi:10.3762/bjoc.20.155

• 1,2,5,6- [9][10] and 2,3,6,7-naphthalene diimides (NDIs) have been produced and utilized in electronically active polymers (Figure 1). The linear extension of 1,4,5,8-naphthalene diimide to produce tetracene [11] and hexacene [12] diimides, some with interesting properties such as near-IR absorption, has

• absorption spectra of the diimides dissolved in CH2Cl2 are depicted in Figure 3a. All of these compounds exhibit broad absorption bands. 7-Hex has more well-defined features with λmax = 391 nm while 7-Ph has a slightly longer wavelength absorption with λmax = 398 nm. A similar trend is observed for 8-Hex and

• 8-Ph, with λmax = 489 and 499 nm, respectively. These absorption features are roughly comparable to other naphthalene and anthracene diimides that have been reported in the literature. The emission profiles of all four compounds are shown in Figure 3b. While N,N’-dibutyl-1,4,5,8-naphthalene diimide

Synthesis of polycyclic aromatic quinones by continuous flow electrochemical oxidation: anodic methoxylation of polycyclic aromatic phenols (PAPs)

• Hiwot M. Tiruye,
• Solon Economopoulos and
• Kåre B. Jørgensen

Beilstein J. Org. Chem. 2024, 20, 1746–1757, doi:10.3762/bjoc.20.153

• indicated, are given in Supporting Information File 1. The optical properties of the PAPs were investigated by UV–vis absorption spectroscopy in 10−5 M solutions in CH2Cl2, as depicted in Figure 1. The UV–vis spectra of these compounds exhibited strong absorption in the region of 250–370 nm. These

• absorption bands are associated with π–π* and n–π* electronic transitions. The optical bandgap (Eg-opt) values of the compounds determined from the absorption edge of the solution spectra are also summarized in Table 5. Although both HOMO and LUMO slightly vary between the compounds, the energy differences

A fiber-optic spectroscopic setup for isomerization quantum yield determination

• Anouk Volker,
• Jorn D. Steen and
• Stefano Crespi

Beilstein J. Org. Chem. 2024, 20, 1684–1692, doi:10.3762/bjoc.20.150

• be obtained from the UV–vis absorption spectra. We show that our results for the prototypical photoswitch azobenzene are in excellent agreement with the literature. The analysis of the errors showed that the quantum yields determined using this method are in the same order of magnitude as when using

• , azobenzene and its derivatives [3][4] have found numerous applications in the development of novel materials [5][6], photopharmacology [7][8][9] but also as actinometers [10][11], due to the large geometry changes upon isomerization [12] and easily accessible derivatives [1][7][13][14]. The absorption

• is the dependence of the Φ on the irradiation wavelength [25]. Clear differences are reported between irradiation of the different absorption bands, due to the so-called anti-Kasha behavior of this molecule, i.e., the wavelength dependency of the quantum yield of reaction [22][24]. Despite its

Methyltransferases from RiPP pathways: shaping the landscape of natural product chemistry

• Maria-Paula Schröder,
• Isabel P.-M. Pfeiffer and
• Silja Mordhorst

Beilstein J. Org. Chem. 2024, 20, 1652–1670, doi:10.3762/bjoc.20.147

• perform oxygen-directed methylation [59]. A range of natural products are known to undergo O-methylation [61], improving membrane permeability, absorption, and oral bioavailability [61][62]. The most extensively studied O-MTs are those that methylate catecholic hydroxy groups [63]. Several O-methylation

New triazinephosphonate dopants for Nafion proton exchange membranes (PEM)

• Fátima C. Teixeira,
• António P. S. Teixeira and
• C. M. Rangel

Beilstein J. Org. Chem. 2024, 20, 1623–1634, doi:10.3762/bjoc.20.145

• usually the best weight loading for doped Nafion membranes. The FTIR-ATR spectra of Nafion membranes (Supporting Information File 1, Figure S1) showed the characteristic very strong and broad absorption bands of Nafion near 1200 and 1145 cm−1 due to the C–F stretching vibration [59][60][61][62][63]. The

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• moiety. The excellent photoswitchability in organic medium and the photoresponsiveness in aqueous medium, driven by visible light, were investigated by UV–vis absorption spectroscopy. The assembled supramolecular nanostructures were confirmed by electron microscopy, while the supramolecular packing was

• , Figures S13–S33. Photochemical properties of DAn in organic medium The photochemical properties of DAn were first studied in organic solvent by UV–vis absorption spectroscopy. The synthesized DA11 in THF solution (20 µM) showed a strong absorption band at 470–685 nm in the UV–vis absorption spectrum

• (Figure 1a). Upon 625 nm red-light irradiation for 60 s at 20 °C to reach the photostationary state (PSS), the strong absorption band at 470–685 nm was diminished, with a clear isosbestic point at 259 nm (Figure 1a, red line), which indicates a selective photoisomerization process from the open-isomer O

Towards an asymmetric β-selective addition of azlactones to allenoates

• Behzad Nasiri,
• Ghaffar Pasdar,
• Paul Zebrowski,
• Katharina Röser,
• David Naderer and
• Mario Waser

Beilstein J. Org. Chem. 2024, 20, 1504–1509, doi:10.3762/bjoc.20.134

• reported in terms of frequency of absorption (cm−1). HPLC was performed using a Shimadzu Prominence system with a diode array detector with a CHIRALPAK AD-H, CHIRAL ART Amylose-SA, (250 × 4.6 mm, 5 µm) chiral stationary phase. Optical rotations were recorded on a Schmidt + Haensch Polarimeter Model UniPol

Photoswitchable glycoligands targeting Pseudomonas aeruginosa LecA

• Yu Fan,
• Ahmed El Rhaz,
• Stéphane Maisonneuve,
• Emilie Gillon,
• Maha Fatthalla,
• Franck Le Bideau,
• Guillaume Laurent,
• Samir Messaoudi,
• Anne Imberty and
• Juan Xie

Beilstein J. Org. Chem. 2024, 20, 1486–1496, doi:10.3762/bjoc.20.132

• irradiation cycles (Figure 2). According to the absorption spectra (Figure 2, black line), the E-isomer shows a relatively strong π→π* transition (λmax = 353 nm) and a weaker forbidden n→π* transition (λmax ≈ 440 nm). After irradiation at 370 nm to induce the E-to-Z photoisomerization, the band at 353 nm

•  1). All the photophysical properties of compounds 1–5 are summarized in Table 1 (spectra are shown in Figure S1–S24 in Supporting Information File 1). Concerning the meta-substituted azobenzene 2, a 30 nm blue shift is observed for the π→π* transition (λmax = 321 nm) as well as a lower absorption

• ). The S-galactosyl azobenzenes 3–5 also displayed excellent photoswitching properties, with a red shift for the π→π* transition (λmax = 348–364 nm) compared to the O-galactosyl derivatives (Table 1, entries 5–8). However, the absorption coefficient and the thermostability of the Z-isomers are increased

Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C–O bonds in organic transformations

• Mithu Roy,
• Bitan Sardar,
• Itu Mallick and
• Dipankar Srimani

Beilstein J. Org. Chem. 2024, 20, 1348–1375, doi:10.3762/bjoc.20.119

• targeted absorption wavelength, and the overall efficacy. Researchers continue to explore and design photocatalysts to enhance the performance in various photocatalytic applications. Visible-light-induced photoredox catalysis has been used in a variety of chemical reactions, including C–C, C–N, C–O, and C

Diameter-selective extraction of single-walled carbon nanotubes by interlocking with Cu-tethered square nanobrackets

• Guoqing Cheng and
• Naoki Komatsu

Beilstein J. Org. Chem. 2024, 20, 1298–1307, doi:10.3762/bjoc.20.113

• square nanobrackets, is designed, synthesized and applied to single-walled carbon nanotubes (SWNTs) for their diameter-based separation. The complexation between copper ions and dipyrrin moieties of the nanobracket gives Cu-tethered square nanobrackets, which is confirmed by absorption, Raman and MALDI

• recovered through demetalation of the interlocked ones along with the nanobracket. Raman and absorption spectroscopies of the extracted SWNTs reveals the diameter enrichment of only several kinds of SWNTs in the diameter range from 0.94 to 1.10 nm among ≈20 kinds of SWNTs from 0.76 to 1.20 nm in their

• extraction, the square Cu-nanobrackets 1b were successfully obtained by the reaction between the nanobracket 4b and copper(II) acetylacetonate in THF at room temperature. The product was characterized as 1b by MALDI-TOF mass spectrometry (Figure 1a), absorption (Figure 1b) and Raman (Figure 2c

Synthesis of indano[60]fullerene thioketone and its application in organic solar cells

• Yong-Chang Zhai,
• Shimon Oiwa,
• Shinobu Aoyagi,
• Shohei Ohno,
• Tsubasa Mikie,
• Jun-Zhuo Wang,
• Hirofumi Amada,
• Koki Yamanaka,
• Kazuhira Miwa,
• Naoyuki Imai,
• Takeshi Igarashi,
• Itaru Osaka and
• Yutaka Matsuo

Beilstein J. Org. Chem. 2024, 20, 1270–1277, doi:10.3762/bjoc.20.109

• around 1000 cm−1 for t-Bu-FIDS. Ultraviolet–visible (UV–vis) spectroscopy of t-Bu-FIDS in o-DCB exhibited two prominent UV absorption bands with peaks at 257 nm and 320 nm (Figure 1b). The absorption at 257 nm indicated the integrity of the fullerene cage chromophore. The absorption peak at 320 nm was

• assigned to the charge transfer band of the C=S bond in t-Bu-FIDS, which was stronger than that of the C=O bond in t-Bu-FIDO [30]. Interestingly, the maximum absorption band observed in t-Bu-FIDO at 432 nm, which is a characteristic feature of 58π-fullerene derivatives with a 1,2-addition pattern, was

Synthesis and optical properties of bis- and tris-alkynyl-2-trifluoromethylquinolines

• Stefan Jopp,
• Franziska Spruner von Mertz,
• Peter Ehlers,
• Alexander Villinger and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 1246–1255, doi:10.3762/bjoc.20.107

• steady state absorption and fluorescence spectroscopy which give insights of the influence of the substitution pattern and of the type of substituents on the optical properties. Keywords: alkynes; catalysis; fluorescence; heterocycles; palladium; Introduction Quinoline is a well-known core structure

• –10°. Optical properties Steady-state absorption and fluorescence measurements were carried out. Compounds 6a, 9a, and 12a were selected to study the impact of the position of the alkynyl group on the optical properties. Comparison of the absorption and emission features of 12a, 12b and 12c gives

• accordance with similar poly-alkynylated molecules from the literature [31][36]. Differences in the absorption and photoluminescence spectra of 6a, 9a and 12a can be explained by the different positions of the alkyne moieties (Figure 5). All absorption spectra exhibit a broad first absorption band with

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• potentials of Aza-H and the substrates and initial steady-state fluorescence quenching experiments (Scheme 1, left), but detailed mechanistic insights and direct evidence of the transient radical ions could not be obtained yet [45]. Figure 1A illustrates the absorption and emission spectra of Aza-H in MeCN

• cage escape quantum yields [67][68]. Aza-H exhibits a relatively long singlet lifetime of 9.6 ns (see Figure 4E), which is sufficient for diffusion-controlled energy or electron transfer at moderate substrate concentrations. Transient absorption (TA) spectra of an Ar-saturated Aza-H solution were

• as the ionization product resulting from a consecutive two-photon absorption at the selected high laser intensity [69][70], yielding the corresponding long-lived radical cation with second-order decay that is typical for oxidized/reduced species, and a solvated electron as by-product. The latter is

Introduction of peripheral nitrogen atoms to cyclo-meta-phenylenes

• Koki Ikemoto and
• Hiroyuki Isobe

Beilstein J. Org. Chem. 2024, 20, 1207–1212, doi:10.3762/bjoc.20.103

• appearing at 250 nm (Figure 2). As shown with the reference spectra of [6]CMP and [8]CMP, the absorption at 280 nm was absent for the corresponding hydrocarbon congeners. These results showed that the nitrogen-dopants induced novel transitions for photoexcitation. Crystallographic analyses revealed the

• acid was necessary for this effect to be observed with a maximum equivalent of TFA at 2 × 105, and the absorption band at the longest wavelength gradually shifted as shown in Figure 5a. When we added TFA to a solution of a reference compound 6 having inward-focused nitrogen atoms with a maximum

• equivalent of TFA at 2 × 105 [13], bathochromic shifts were also observed. However, unlike the case with 3a, gradual absorption shifts were not observed, and the absorption changed from 299 nm to 320 nm with an isosbestic point at 303 nm as shown in Figure 5b. This observation indicated that the protonation

Cofactor-independent C–C bond cleavage reactions catalyzed by the AlpJ family of oxygenases in atypical angucycline biosynthesis

• Jinmin Gao,
• Liyuan Li,
• Shijie Shen,
• Guomin Ai,
• Bin Wang,
• Fang Guo,
• Tongjian Yang,
• Hui Han,
• Zhengren Xu,
• Guohui Pan and
• Keqiang Fan

Beilstein J. Org. Chem. 2024, 20, 1198–1206, doi:10.3762/bjoc.20.102

• + AlpJ; (d) 8 + AlpJ + SOD (5,000 U/mL); (e) 8 + Flu17 + SOD (5,000 U/mL). UV absorption at 266 nm (black line) and 313 nm (red line) are displayed for each reaction. Ring cleavage and ring rearrangement reactions in the biosynthesis of atypical angucyclines. Proposed catalytic mechanism of cofactor

Two-fold addition reaction of silylene to C₆₀: structural and electronic properties of a bis-adduct

• Masahiro Kako,
• Masato Kai,
• Masanori Yasui,
• Michio Yamada,
• Yutaka Maeda and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2024, 20, 1179–1188, doi:10.3762/bjoc.20.100

• ) spectrum. Fullerene derivatives are well-known to show characteristic absorption spectra depending on the addition pattern. As shown in Figure 2, the spectrum of 3 exhibited an absorption maximum at 515 nm, which is similar to those of the e′ and e′′ isomers of C60[C(C6H4OMe)2]2 and C60[C(C6H4OMe)2][NCOOEt

• . Reagents were used as purchased unless otherwise specified. The 1H and 13C NMR measurements were conducted on a JEOL ECA-500 spectrometer (JEOL Ltd.). Absorption spectra were measured using a UV-3150 spectrophotometer (Shimadzu Corp.). Cyclic voltammograms and differential pulse voltammograms were recorded

• ) Å3, T = 99.9(2) K, Z = 4, 67750 reflections measured, 19176 unique (Rint = 0.0321), which were used for all calculations, 2θmax = 63.262; min/max transmission = 0.921/1.000 (absorption correction was applied by multi-scan method); The structure was solved using a direct method using olex2.solve 1.5

Kinetically stabilized 1,3-diarylisobenzofurans and the possibility of preparing large, persistent isoacenofurans with unusually small HOMO–LUMO gaps

• Qian Liu and
• Glen P. Miller

Beilstein J. Org. Chem. 2024, 20, 1099–1110, doi:10.3762/bjoc.20.97

• isobenzofurans 2, 3 and 23 were studied by UV–vis and fluorescence spectroscopies (Figure 5). Compound 2 is devoid of ortho groups on its 1,3-diphenyl substituents and shows the longest wavelengths of absorption (λmax = 415 nm) and emission (emission λmax = 484 nm) in this series, consistent with a more highly

• conjugated π-system in which the 1,3-diphenyl substituents lie flat or nearly flat relative to the isobenzofuran backbone. Likewise, compound 2 is yellow while compounds 3 and 23 are colorless. Compounds 3 and 23 show similar absorption (λmax = 364 and 360 nm for 3 and 23, respectively) and emission (λmax

• Center using a peak-matching protocol to determine the mass and error range of the molecular ion, and employing electrospray as the ionization technique. UV–vis absorption spectra were measured with a Varian Cary 50 Scan UV–visible spectrophotometer and corrected for background signal with a solvent

Novel route to enhance the thermo-optical performance of bicyclic diene photoswitches for solar thermal batteries

• Akanksha Ashok Sangolkar,
• Rama Krishna Kadiyam and
• Ravinder Pawar

Beilstein J. Org. Chem. 2024, 20, 1053–1068, doi:10.3762/bjoc.20.93

• barriers were accounted using the DLPNO-CCSD(T) and (8,8)-CASPT2 methods, respectively. The photophysical properties including the absorption onset, excitation wavelengths, and the absorption intensities were extensively investigated with the time-dependent calculations. The result provides information on

• modification, the storage energy of 158.57 kJ/mol, energy storage density of 1.48 MJ/kg, TBR barrier of 136.36 kJ/mol, and the absorption onset of 305.00 nm is achieved in acetonitrile. These values are substantially higher when compared with the storage energy (96.06 kJ/mol), energy storage density (1.04 MJ

• photoswitching is depicted in Figure 1a. The NBD/QC couple is capable to chemically store huge amounts of solar energy due to the incorporation of large strain during the photoconversion and is thus recognized as a potential MOST candidate [8][9][10][13]. However, the optical absorption of unsubstituted NBD in

Structure–property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives

• Tural N. Akhmedov,
• Ajeet Kumar,
• Daken J. Starkenburg,
• Kyle J. Chesney,
• Khalil A. Abboud,
• Novruz G. Akhmedov,
• Jiangeng Xue and
• Ronald K. Castellano

Beilstein J. Org. Chem. 2024, 20, 1037–1052, doi:10.3762/bjoc.20.92

• and its high thermal stability. Optical properties The electronic properties of the DCPQs 1a–6a and DPQDs 1b–7b were explored by UV–vis absorption spectroscopy in dimethyl sulfoxide (DMSO) at 25 °C (Figure 3). The electronic absorption spectra of DCPQs exhibited structureless bands with λmax values

• 40 μM solutions of the DCPQs and DPQDs on a Cary 100 Bio spectrophotometer using 1 cm quartz cells. All solvents were HPLC grade (purchased from Fisher) and stored over 4 Å molecular sieves. The absorption intensity at λmax was then plotted against the concentration in all cases to confirm, by

• of electron-accepting azaacene derivatives as liquid-crystalline materials by Takeda et al. (b) [24]. Transformation of Yamashita’s DCPQs to H-bonding capable DPQD derivatives discussed in this work (c) [25]. TGA of 1a–6a (a) and 1b–7b (b) obtained at 10 °C/min under nitrogen. Absorption spectra (20

Spin and charge interactions between nanographene host and ferrocene

• Akira Suzuki,
• Yuya Miyake,
• Ryoga Shibata and
• Kazuyuki Takai

Beilstein J. Org. Chem. 2024, 20, 1011–1019, doi:10.3762/bjoc.20.89

• ). Here, it should be noted that the vibrational spectra are more distorted due to electromagnetic shielding effects by the conductive nature of graphene-based materials upon IR excitation. Thus, the “apparent” negative absorption peak in the spectrum of FeCp2-ACFs-55 is caused by the phase shift of the