Fluorine-Containing Dibenzoanthracene and Benzoperylene-Type Polycyclic Aromatic Hydrocarbons: Synthesis, Structure, and Basic Chemical Properties

Abstract

Intramolecular photocyclization of stilbene derivatives (Mallory reaction) is one of the efficient methods for building polycyclic aromatic hydrocarbon (PAH) frameworks, and is also expected to be applicable to synthesis of fluorine-containing PAHs (F-PAHs). In this study, dibenzoanthracene-type (4a) and benzoperylene-type (4b) F-PAHs were synthesized using the Mallory reaction of the 1,4-distyrylbenzene-type π-conjugated molecule (3a), which was prepared by addition-defluorination of available octafluorocyclopentene (OFCP) and aryllithium in three steps. The structure of 4a originating from π–π interaction was characterized by X-ray crystallographic analysis. The absorption maxima of UV-Vis spectra and emission maxima of photoluminescence spectra of the PAHs were positioned at a longer wavelength compared to those of the corresponding unsubstituted PAHs, presumably due to the electron-withdrawing nature of perfluorocyclopentene (PFCP) units. The effect of PFCP units in F-PAHs was also studied by time-dependent density functional theory (TD-DFT) calculation.

1. Introduction

Fluorine-containing polycyclic aromatic hydrocarbons (F-PAHs) [1] have attracted much attention in the field of material chemistry as n-type semiconductors for fabrication of electronic and optical devices [2]. In order to synthesize F-PAHs in short steps, it is inevitable to introduce fluorine or organofluorine groups into the PAH framework. Direct fluorination of PAH with a fluorinated reagent [3,4] is a typical and simple synthetic method, however it requires expensive XeF₂ [3] or treatment of a fluorinated reagent (e.g., N-fluoro-2,4-dinitroimidazole) using F₂ gas [4]. Furthermore, this method usually yields a mixture of regioisomers of F-PAHs, due to the difficulty of selective fluorination to the mother PAH skeleton, except for a few cases [5,6]. On the other hand, the ring-closing process of fluorine-containing aromatic compounds can basically achieve the desired regiospecific F-PAH. For example, Ichikawa and his coworkers reported metal-catalyzed Friedel–Crafts-type intramolecular cyclization of difluoroalkene and the nearest phenyl unit [7,8,9]. In this case, fluorine was pinpoint introduced to a phenacene skeleton. Kikuzawa and his groups developed a synthesis of hexafluoro-hexa-peri-hexabenzocoronene, which showed an n-type character in a fabricated FET (field effect transistor) device, using chemical oxidative intramolecular cyclization (Scholl reaction) of the corresponding hexaphenylbenzene [10].

The Mallory reaction is a useful intramolecular photocyclization of stilbene derivatives for synthesis of phenanthrenes via cis-trans isomerization [11,12,13], which is also applicable to the formation of F-PAHs. In recent years, regiospecific F-PAHs have been synthesized by photocyclization of 1,2-diarylfluoroalkenes via Julia−Kocienski olefination [14] or the Wittig reaction [15]. Our group also reported fluorine-containing phenanthrenes [16] using the Mallory reaction of the corresponding stilbene-type precursor, which were obtained by the reaction of available octafluorocyclopentene (OFCP) with two equivalents of aryllithium under milder conditions (addition-defluorination [17]). The merit of addition-defluorination toward fluorine-containing alkene is the stepwise introduction of two different aromatic rings to give an asymmetric diarylethene in only two steps. Therefore, a combination of the Mallory reaction and addition-defluorination has the ability to supply a wide variety of F-PAHs containing perfluorocyclopentene (PFCP) unit(s).

Herein, we report the synthesis of 1,4-distyrylbenzene-like π-conjugated molecule bearing PFCP units by reaction of available OFCP with aryllithium derivatives. We also describe fluorine-containing dibenzoanthracene and benzoperylene using the sequential Mallory reaction of the synthesized precursor.

2. Results

2.1. Synthesis of Fluorine-Containing Dibenzoanthracene (4a) and Benzoperylene (4b)

The synthetic route to fluorine-containing dibenzoanthracene 4a and benzoperylene 4b is shown in Scheme 1. Preparation of 1-phenyl-heptafluorocyclopentene 1 (64%, literature 29% [17]) was carried out by reaction of OFCP and 1 equiv. of phenylmagnesium bromide, according to the literature [17]. Treatment of 1 with 4-bromophenyllithium in THF gave unsymmetric diarylethene 2 as a colorless oil in 52% yield. Lithiated 2, generated from 2 and ⁿBuLi, was reacted with 1 in THF to afford the precursor for the following Mallory reaction, giving 3 as white powder in 22% yield.

Mallory reaction of 3 in benzene was carried out under light irradiation (λ = 365 nm) at room temperature (rt) for 3 h in the presence of iodine (1.6 equiv.) as an oxidant and excess amounts of 1,2-epoxybutane as a scavenger of the formed hydrogen iodide to give the mixture of the ring-closed products 4a and 4b, confirmed by ¹H-NMR spectroscopy. Benzoperylene-type 4b in the reaction mixture was sublimed under reduced pressure (0.1 kPa) at 160 °C, however the sublimate still contained a small amount of dibenzoanthracene-type 4a. The sublimate was purified by preparative layer chromatography (PLC) (silica) to afford pure 4a and 4b (13% yield). After removal of the first sublimate, the residue was heated up to 250 °C under 0.1 kPa to result in sublimation of 4a (22% as total yield); the low yields were due to loss of the products in repeated purification (PLC and sublimation). Compared to the solubility of 3, both 4a and 4b have quite low solubility in organic solvents, such as chloroform and dichloromethane. Formation of [5]helicene-type compound was not detected after the Mallory reaction. It is known that photocyclization of 1,4-distyrylbenzene derivatives preferably gives benzoperylene, [5]helicene, or both, whereas photocyclization affords dibenzoanthracene in low yields [13,18,19]. The above Mallory reaction of 3 indicates that formation of dibenzoanthracene-like structure, and rotation of one of the PFCP units to form benzoperylene-like structure, are competitive as the second photocyclization. It is also supposed that the third photocyclization spontaneously occurred to give benzoperylene-like 4b once the second photocyclization proceeded in [5]helicene-type form.

¹H-NMR spectra of 3, 4a, and 4b are depicted in the Supporting Information. In the spectrum of 3 (Figure S4), signals of two terminal phenyl and central phenylene protons are observed in the typical aromatic region. For spectra of 4a and 4b (Figures S7 and S9), all the peaks clearly appear at a lower magnetic field than those observed in that of 3, owing to the magnetic deshielding effect of the extended π-conjugated PAH framework. In particular, the singlet observed at 9.77 ppm in the spectrum of 4a is assignable to the protons bound to the carbons of the central ring in the dibenzoanthracene framework, due to the induced effect originating from the neighborhood fluorines in the PFCP units.

2.2. Molecular Structures of 3, 4a, and 4b

The molecular structures of 3, 4a, and 4b revealed by X-ray crystallographic study are shown in Figure 1. The structures of precursor 3 and dibenzoanthracene 4a have four and two independent molecules in the unit cell, respectively. One of the independent molecules (molecule A for 3 in Figure 1a and molecule E for 4a in Figure 1b) is depicted in Figure 1 for clarity. Benzoperylene 4b (Figure 1c) and 3 (molecules C and D in Figure 1a) show disorder in fluorine atoms. Precursor 3 takes a flexible backbone with dihedral angle between the central phenylene plane (C3–C8–C21–C3*–C8*–C21*) and the terminal phenyl plane (C25–C34–C44–C49–C45–C33) of 60.2°, to result in no face-to-face π–π interactions between neighborhood molecules (Figure 1a). The C=C bond distance between C5 and C12 in the five-membered unit is 1.353(5) Å (molecule A), which is comparable to the reported similar diarylethene derivatives [20]. For 4a, two independent molecules (molecules E and F) are herringbone-like packed in the unit cell, and one of two independent molecules (molecule E) partly overlaps to make a pair with terminal naphthalene units (C2-C3-C4-C5-C8–C9–C10–C11–C6–C7) in the neighboring molecule; the distance between the centroids in the dibenzoanthracene skeleton is 7.15 Å. The distance between dibenzoanthracene planes is 3.55 Å, due to the π–π interaction (Figure 1b). The shortest intermolecular fluorine–fluorine (F2-F5) distance between the pairing molecules is ca. 2.67 Å, which is shorter than the sum of the van der Waals radius (2.94 Å), indicating that not only the π–π interaction, but also the F–F interaction partly contribute to the packing of the molecules of 4a [21]. The length of the C=C bond (C(3)–C(4)) fused with the perfluorocycloalkane unit is 1.354(5) Å. In the case of 4b, the molecules construct a columnar structure extended to a axis in the crystal (Figure 1c). In sharp contrast to the case of 4a, the nearest two molecules of 4b fully overlap where possible, to avoid steric repulsion between the bulky PFCP units, Such overlap of benzoperilene skeletons is observed in unsubstituted benzoperylene [22] and 1,2-disubstituted benzoperylene [23].

2.3. UV-Vis and Photoluminescence Spectra of 3, 4a, and 4b

UV-Vis and photoluminescence (PL) spectra of 4a and 4b are shown in Figure 2a,b, respectively, and the optical data are summarized in

Table 1. UV-Vis and photoluminescence spectral data of 4a and 4b ^a.

F-PAH	UV-Vis a λmax, nm (ε, M−1 cm−1)	Photoluminescence λem, nm
4a	292 (47000), 301 (64000), 322 (10400), 336 (10000), 352 (11000), 380 (1120), 401 (750)	411, 433
4b	284 (13400), 298 (14600), 309 (17600), 379 (6600), 401 (7100)	418, 440

^a Measured in CH₂Cl₂. ^b [4a] = 1.6 × 10⁻⁵ M and [4b] = 3.1 × 10⁻⁵ M.

. For comparison, UV-Vis and PL spectra of the corresponding precursor 3 were also measured, as depicted in Figure S12. The absorption maximum (λ_max) in the spectrum of 3 appears at 262 nm, due to localization of π-electrons along the flexible backbone of 3. In contrast, the spectra of 4a and 4b in CH₂Cl₂ exhibit λ_max at 301 nm and 309 nm, respectively. This longer wavelength shift presumably originates from extension of the π-conjugated system on the molecules of 4a and 4b. The spectrum of dibenzoanthracene 4a exhibits three medium peaks (ε = ca. 10,000 M⁻¹∙cm⁻¹) at 322, 336, and 352 nm, and two small peaks (ε = ca. 1000 M⁻¹∙cm⁻¹) around 390 nm, as comparable to those observed in unsubstituted dibenzoanthracene [24]. On the other hand, the spectrum of benzoperylene 4b gives two clear peaks (ε = ca. 7000 M⁻¹∙cm⁻¹) around 380 and 400 nm, which is similar to those of the reported analogues [23]. Time-dependent density functional theory (TD-DFT) calculation supports assignments of absorption peaks in the UV-Vis spectrum of organic molecules. The TD-DFT calculation was carried out at the B3LYP/6-311G(d) level, and the initial structures of 4a and 4b were obtained using their X-ray crystallographic data. The results indicate that the bands that appeared at 401 and 309 nm in the spectrum of 4b correspond to the transition from HOMO (the highest occupied molecular orbital) to LUMO (the lowest unoccupied molecular orbital) with oscillator strength (f) of 0.2041 (λ_calc = 399 nm), and the HOMO→LUMO + 1 (f = 0.3049, λ_calc = 307 nm) transition, respectively (Table S1). The DFT calculation also suggests that the HOMO→LUMO + 1 (f = 0.5972, λ_calc = 305 nm) transition corresponds to the large peak (ε = 64,000 M⁻¹∙cm⁻¹) at 301 nm in the spectrum of 4a, and the weak band (ε = 1120 M⁻¹ cm⁻¹) around 380 nm is thought to be the HOMO→LUMO transition (f = 0.0146, λ_calc = 381 nm).

The Mallory reaction products are photoluminescent in CH₂Cl₂ (Figure 2b). The main PL peaks (λ_em) of 4a and 4b appear at 411 and 418 nm, respectively. The λ_em peak positions of both 4a and 4b shift to longer wavelengths than those of the corresponding unsubstituted dibenzoanthracene (λ_em = 398 nm) [24] and benzoperylene (λ_em = 408 nm) [23], respectively. In recent years, it has been reported that introduction of electron-withdrawing methoxycarbonyl group(s) into the C1 and C2 carbons of benzoperylene causes a longer wavelength shift of their PL spectra [23]. In the case of 4b, PFCP units may contribute to the red-shift of the λ_em peak, although the PFCP units are fused on the C3, C4, C11, and C12 carbons of 4b. In contrast, the PL spectrum of precursor 3 exhibited a very weak band at approximately 430 nm in CHCl₃ (Figure S12), due to the small effective π-conjugation length along the distorted molecule of 3.

2.4. Computational Study

To evaluate effect of the introduction of PFCP units to the PAH backbone, a computational study was carried out by DFT at the B3LYP/6-311G(d) level, together with 4a-H* and 4b-H*, in which all the fluorine atoms of 4a and 4b are replaced with hydrogen atoms for comparison (Figure 3). As shown in this diagram, the LUMOs in 4a and 4b are extended to the PFCP units, and their LUMO levels (−2.96 eV for 4a and −3.12 eV for 4b) are remarkably lower than those of 4a-H* (−1.60 eV) and 4b-H* (−1.77 eV). The HOMO levels of 4a (−6.75 eV) and 4b (−6.57 eV) are also lower than those of 4a-H* (−5.36 eV) and 4b-H* (−5.22 eV), due to electro-negative fluorine groups in PFCP units. The HOMO–LUMO gap of benzoperylene-type 4b (3.45 eV) is smaller than that of dibenzoanthracene-type 4a (3.79 eV). This trend is consistent with the difference in the UV-Vis absorption peaks between 4a and 4b, as described above.

3. Materials and Methods

3.1. General

All manipulations were conducted by standard Schlenk techniques in argon atmosphere. ¹H-, ¹³C-, and ¹⁹F-NMR spectra were measured with a Bruker AVANCE III 400 spectrometer (¹H-NMR: 400 MHz, ¹⁹F-NMR: 376 MHz, ¹³C-NMR: 100 MHz; Bruker Corporation, Billerica, MA, USA). SiMe₄ was used as an internal standard for ¹H- and ¹³C-NMR spectra, and CFCl₃ was adopted as an external standard for ¹⁹F-NMR spectra. UV-Vis and photoluminescence spectra were recorded on a Shimadzu UV-3100PC spectrometer (Shimadzu Corporation, Kyoto, Japan) and a Hitachi F-4500 spectrometer (Hitachi High-Technologies Corporation, Tokyo, Japan), respectively. Elemental analysis was carried out using a J-Science Lab JM10 microanalyzer (J-Science Lab Co., Ltd., Kyoto, Japan). High resolution mass spectra (HRMS) were taken using a JEOL JMS-700 analyzer (JEOL Ltd., Akishima, Japan). Mallory reaction of 3 was conducted using a USHIO Optical Modulex Multi-purpose lighting unit (irradiation wavelength = 365 nm, light power = 20 mW/cm²; USHIO INC., Tokyo, Japan). Octafluorocyclopentene (OFCP) was purchased and used without further purification. 1-Phenyl-heptafluorocyclopentene (1) was prepared according to the literature [17].

3.2. Synthesis of 1-(4-bromophenyl)-2-phenyl-3,3,4,4,5,5-hexafluorocyclopentene (2)

To a THF (10 mL) solution of 1,4-dibromobenzene (0.71 g, 3.0 mmol), ⁿBuLi (1.6 M hexane solution, 1.9 mL, 3.0 mmol) at −78 °C was added, and the reaction temperature was kept at −78 °C for 20 min. 1 (0.81 g, 3 mmol) was added to the reaction mixture at −78 °C, then the reaction temperature was raised up to rt for 1 h. The reaction mixture was poured into saturated NH₄Cl aqueous solution (ca. 10 mL) and extracted with ethyl acetate (ca. 60 mL). The organic layer was washed with distilled water and dried over MgSO₄. The solvent was removed at reduced pressure, and the resulting residue was purified by column chromatography on silica (eluent = hexane) to afford 2 as a colorless oil (0.63 g, 52%). ¹H-NMR (400 MHz, CDCl₃): δ 7.50–7.55 (m, 2H), 7.44–7.30 (m, 5H), 7.20 (d, J = 8.8 Hz, 2H). ¹³C{¹H}-NMR (100 MHz, CDCl₃): δ 140.26 (m), 138.50 (m), 132.26, 130.84, 130.54, 129.21, 129.06, 127.46, 126.66, 125.04, 116.33 (triplet of triplets (tt), J = 255.7 and 23.9 Hz), 111.07 (tt, J = 269.7 and 25.0 Hz). The central CF₂ carbon in the five-membered ring was not clearly observed, presumably because the intensity of the peak with multicity became very weak. ¹⁹F-NMR (376 MHz, CDCl₃): δ −110.38 (m, 2F), −110.60 (m, 2F), −131.66 (m, 2F). HRMS (FAB positive, m/z): Found, 406.9868; calcd. for C₁₇H₁₀BrF₆ ([M + H]⁺), 406.9825.

3.3. Synthesis of 1,1′-[1,4-phenylenebis(3,3,4,4,5,5-hexafluorocyclopent-1-ene-2,1-diyl)]dibenzene (3)

To a THF (5 mL) solution of 2 (0.63 g, 1.5 mmol), ⁿBuLi (1.6 M hexane solution, 0.9 mL, 1.5 mmol) at −78 °C was added, and the reaction temperature was kept at −78 °C for 30 min. After consumption of 2, 1 (0.41 g, 1.5 mmol) was added to the reaction mixture at −78 °C. The reaction temperature was kept at −78 °C for 1 h, and then raised up to rt for 1 h. The reaction mixture was poured into saturated NH₄Cl aqueous solution (ca. 5 mL) and extracted with ethyl acetate (ca. 60 mL). The organic layer was washed with distilled water and dried over MgSO₄. The solvent was removed at reduced pressure, and the resulting residue was purified by column chromatography on silica (eluent = hexane) to give 3 as white powder (0.19 g, 22%). ¹H-NMR (400 MHz, (CD₃)₂CO): δ 7.58–7.45 (m, 10H), 7.43 (d, J = 7.6 Hz, 4H). ¹³C{¹H}-NMR (100 MHz, (CD₃)₂CO): δ 141.33 (m), 138.87 (m), 130.83, 130.00, 129.63, 129.24, 129.08, 127.04, 116.42 (tt, J = 256.4 and 21.8 Hz), 111.29 (tt, J = 269.6 and 24.9 Hz). The central CF₂ carbon in the five-membered ring was not clearly observed, presumably because the intensity of the peak with multicity became very weak. ¹⁹F-NMR (376 MHz, (CD₃)₂CO): δ −110.04 to −110.07 (m, 4F), −110.37 to −111.41 (m, 4F), −132.36 (quint, J = 4.5 Hz, 4F). Found: C, 58.17; H, 2.68. Calcd. for C₂₈H₁₄F₁₂: C, 58.14; H, 2.44.

3.4. Synthesis of 1,1,2,2,3,3,9,9,10,10,11,11-dodecafluoro-1,2,3,9,10,11-hexahydrobenzo[k]dicyclopenta[f,m]tetraphene (4a) and 1,1,2,2,3,3,10,10,11,11,12,12-dodecafluoro-1,2,3,10,11,12-hexahydrobenzo[pqr]dicyclopenta[b,n]perylene (4b)

To a mixture of 3 (0.042 g, 0.073 mmol) and benzene (30 mL), iodine (0.029 g, 0.12 mmol) at rt was added in Ar atmosphere. After stirring for 30 min, 1,2-epoxybutane (0.3 mL, 3.5 mmol) was added to the mixture, which was stirred under light irradiation at rt for 3 h. The reaction mixture was poured into saturated sodium thiosulfate aqueous solution (10 mL), and the resulting organic layer was washed with distilled water (10 mL) and brine (10 mL). After separation and drying of the layer, the solvent was evaporated at reduced pressure. The resulting residue was heated under 0.1 kPa at 160 °C, and the sublimate was separated by column chromatography on silica (eluent: ethyl acetate/hexane = 1/4) to afford 4a and 4b. The residue after the first sublimation was heated again under 0.1 kPa at 250 °C to sublime 4a. 4a—colorless powder (10 mg, 22%). ¹H-NMR (400 MHz, CDCl₃): δ 9.77 (s, 2H), 9.01 (d, J = 8.0 Hz, 2H), 8.49 (d, J = 7.2 Hz, 2H), 8.07 (t, J = 7.2 Hz, 2H), 7.93 (t, J = 8.0 Hz, 2H). ¹⁹F-NMR (376 MHz, CDCl₃): δ −105.45 (m, 4F), −106.06 (m, 4F), −128.75 (quint, J = 3.8 Hz, 4F). HRMS (FAB positive, m/z): Found, 574.0552; Calcd. for C₂₈H₁₀F₁₂ ([M]⁺), 574.0591. 4b—colorless powder (6 mg, 13%). ¹H-NMR (400 MHz, CDCl₃): δ 9.34 (d, J = 8.0 Hz, 2H), 9.05 (s, 2H), 8.83 (d, J = 8.0 Hz, 2H), 8.35 (t, J = 8.0 Hz, 2H). ¹⁹F-NMR (376 MHz, CDCl₃): δ −105.61 (m, 4F), −106.17 (m, 4F), −128.7 (t, J = 3.8 Hz, 4F). HRMS (FAB positive, m/z): Found, 572.0458; Calcd. for C₂₈H₈F₁₂ ([M]⁺), 572.0434.

3.5. X-Ray Crystallographic Analysis of 3, 4a, and 4b

Single crystals of 3, 4a, and 4b suitable for X-ray crystallographic analysis were obtained by slow evaporation of the saturated CH₂Cl₂ (for 4a and 4b) or hexane (for 3) solution at rt. The crystals were mounted on a Rigaku XtaLabMini diffractometer (Rigaku Corporation, Akishima, Japan) using Mo Kα radiation (λ = 0.71073 Å). Processing of the collected reflection data was carried out using the CrysAlisPro program (version 1.171.38.46, Rigaku Corporation, Akishima, Japan) [25]. The structure was solved by a direct method (SHELXT-2014/5) and refined by the full-matrix least square method on F² for all reflections (SHELXTL-2014/7) [26]. All hydrogen atoms were placed using AFIX instructions, and all the other atoms were refined anisotropically. Precursor 3 and benzoperylene 4b showed disorder in fluorine atoms (F25, F26, F27, F28, in 3; F9 and F10 in 4b). Dibenzoanthracene 4a and 3 have two and four independent molecules in the unit cell, respectively. Crystallographic data of 3, 4a, and 4b are deposited on the system of The Cambridge Crystallographic Data Centre: CCDC-1822475 (for 3), CCDC-1822473 (for 4a), and CCDC-1822474 (for 4b). These crystal data can be obtained free of charge from the center via https://www.ccdc.cam.ac.uk/structures/.

Crystal data for 3: C₂₈H₁₄F₁₂, FW 578.39, –100 °C, 0.130 × 0.120 × 0.120 mm³, Triclinic, P-1, a = 10.1230(5) Å, b = 13.9273(9) Å, c = 18.2364(11) Å, V = 2414.6(3) ų, α = 70.087(6)°, β = 88.323(5)°, γ = 87.402(5)°, Z = 4, D_calcd = 1.591 g cm⁻³, μ = 0.157 mm⁻¹, F(000) = 1160, 2.014° ≤ θ ≤ 25.500°, reflection collected 21,605, independent reflections 8993 (R_int = 0.0373), completeness to θ_max 100.0%, data/restraints/parameters 8993/48/793, GOF on F² 1.027, R₁ [I > 2σ(I)] 0.0710, wR² (all data) 0.2046, largest diffraction peak and hole 0.871 and −0.464 e Å⁻³.

Crystal data for 4a: C₂₈H₁₀F₁₂, FW 574.36, −100 °C, 0.230 × 0.180 × 0.150 mm³, Triclinic, P-1, a = 7.1452(7) Å, b = 9.4617(7) Å, c = 17.8343(15) Å, V = 1088.81(18) ų, α = 79.109(7)°, β = 79.718(8)°, γ = 67.831(8)°, Z = 2, D_calcd = 1.752 g cm⁻³, μ = 0.174 mm⁻¹, F(000) = 572, 2.342° ≤ θ ≤ 25.492°, reflection collected 9765, independent reflections 4065 (R_int = 0.0508), completeness to θ_max 99.9%, data/restraints/parameters 4065/0/361, GOF on F² 1.031, R₁ [I > 2σ(I)] 0.0634, wR² (all data) 0.1985, largest diffraction peak and hole 0.365 and −0.357 e Å⁻³.

Crystal data for 4b: C₂₈H₈F₁₂, FW 572.34, −100 °C, 0.210 × 0.080 × 0.050 mm³, Triclinic, P-1, a = 7.438(3) Å, b = 11.078(3) Å, c = 13.181(3) Å, V = 1024.6(6) ų, α = 72.22(3)°, β = 82.50(3)°, γ = 89.76(3)°, Z = 2, D_calcd = 1.855 g cm⁻³, μ = 0.184 mm⁻¹, F(000) = 568, 1.638° ≤ θ ≤ 25.495°, reflection collected 9075, independent reflections 3811 (R_int = 0.1310), completeness to θ_max 100.0%, data/restraints/parameters 3811/54/379, GOF on F² 1.058, R₁ [I > 2σ(I)] 0.1448, wR² (all data) 0.4404, largest diffraction peak and hole 0.963 and −0.676 e Å⁻³. The ratio of observed unique reflection is 45% and R value is over 10%. Thus, crystallographic data of 4b can only be used for molecular structure identification as shown in Figure 1c and as the starting molecule for DFT optimization (Figure 3).

3.6. Computational Method

DFT calculations were performed using the Gaussian 16 program package (Gaussian, Inc., Wallingford, CT, USA) [27]. The initial geometry of the structures of 4a and 4b using their X-ray crystallographic data was optimized at the B3LYP/6-311G(d) level of theory. The computational time was provided by the Super Computer Laboratory, Institute for Chemical Research, Kyoto University. Frequency calculations confirmed that all the optimized geometries are the equilibrium structures. Excited energies and oscillator strengths were calculated on the optimized structures by the TD-DFT method at the B3LYP/6-311G(d) level. Tables S2, S3, S4, and S5 in the supporting information show Cartesian coordinates of the optimized geometries of 4a, 4a-H*, 4b, and 4b-H*, respectively.

4. Conclusions

In conclusion, we investigated efficient synthesis of fluorine-containing dibenzoanthracene (4a) and benzoperylene (4b) using Mallory reaction of the corresponding 1,4-distyrylbenzene-type precursor (3), which was prepared using addition-defluorination of available OFCP and aryllithium derivatives. The structure of 4a originating from intermolecular π–π interactions was characterized by X-ray crystallographic analysis. In the structure of 4a, the F–F interaction between the nearest molecules was observed. UV-Vis spectra of 4a and 4b in CH₂Cl₂ exhibited λ_max at 301 and 309 nm, respectively. The main PL peaks (λ_em) of 4a and 4b in CH₂Cl₂ appeared at 411 and 418 nm, respectively, which shifted to longer wavelengths compared to those of the corresponding unsubstituted dibenzoanthracene and benzoperylene. The effect of electron-withdrawing PFCP units in 4a and 4b skeletons was also evaluated by computational study; TD-DFT calculation of 4a and 4b revealed that both HOMO and LUMO levels became lower than those of the corresponding non-fluorinated 4a-H* and 4b-H*. This finding will contribute to the design of new n-type F-PAHs.