Pinpoint-fluorinated polycyclic aromatic hydrocarbons (F-PAHs): Syntheses of difluorinated subfamily and their properties

Article abstract of DOI:10.1016/j.jfluchem.2017.09.002

Difluorinated polycyclic aromatic hydrocarbons (PAHs) containing three to five benzene rings were systematically synthesized by the Pd(II)-catalyzed Friedel–Crafts-type cyclization of 1,1,2-trifluoro- and 1,1-difluoro-1-alkenes and the In(III)-catalyzed tandem cyclization of bis(1,1-difluoroallene)s. Using an array of the difluorinated PAHs that were obtained and previously reported monofluorinated PAHs, the physical properties of the pinpoint-fluorinated PAHs were investigated. (i) The ¹⁹F NMR signals of the bay-region fluorine atoms were shifted downfield by ca. 8–14 ppm for vic-difluorinated PAHs and ca. 11–19 ppm for non-vic-difluorinated and monofluorinated PAHs. (ii) The introduction of fluorine into PAH molecules increased their solubilities in organic solvents, which was best exemplified by the high solubilities of 6,7-difluoropicene (5.4 wt%) and 6-fluoropicene (5.3 wt%) in THF. (iii) The HOMO–LUMO energy gaps of the pinpoint-fluorinated PAHs were smaller than that of the corresponding fluorine-free PAH (i.e., picene) by 0.02–0.26 eV, and the HOMO and LUMO energy levels were lowered by 0.10–0.22 eV and 0.12–0.41 eV, respectively.

Full text of DOI:10.1016/j.jfluchem.2017.09.002

Accepted Manuscript
Title: Pinpoint-fluorinated polycyclic aromatic hydrocarbons
(F-PAHs): Syntheses of difluorinated subfamily and their
properties
Authors: Kohei Fuchibe, Kento Shigeno, Nan Zhao, Hiromichi
Aihara, Rikuo Akisaka, Toshiyuki Morikawa, Takeshi Fujita,
Kie Yamakawa, Toshihiro Shimada, Junji Ichikawa
PII:
S0022-1139(17)30371-8
DOI:
Reference:
http://dx.doi.org/10.1016/j.jfluchem.2017.09.002
FLUOR 9043
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Received date:
Revised date:
Accepted date:
20-8-2017
3-9-2017
3-9-2017
Please cite this article as: Kohei Fuchibe, Kento Shigeno, Nan Zhao, Hiromichi
Aihara, Rikuo Akisaka, Toshiyuki Morikawa, Takeshi Fujita, Kie Yamakawa, Toshihiro
Shimada, Junji Ichikawa, Pinpoint-fluorinated polycyclic aromatic hydrocarbons (F-
PAHs): Syntheses of difluorinated subfamily and their properties, Journal of Fluorine
Chemistryhttp://dx.doi.org/10.1016/j.jfluchem.2017.09.002
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1
Pinpoint-fluorinated Polycyclic Aromatic Hydrocarbons (F-PAHs): Syntheses of Difluorinated
Subfamily and Their Properties
Kohei Fuchibea, Kento Shigenoa, Nan Zhaoa, Hiromichi Aiharaa, Rikuo Akisakaa, Toshiyuki Morikawaa,
Takeshi Fujitaa, Kie Yamakawab, Toshihiro Shimadab, and Junji Ichikawaa*
a Division of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki
305-8571, Japan
b
Division of Applied Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo,
Hokkaido 060-8628, Japan
Dedicated to Professor Antonio Togni with recognition on the occasion of his being awarded the 2017
ACS Award for Creative Work in Fluorine Chemistry.
Graphical Abstract
(Pictogram)
(Synopsis)
Difluorinated polycyclic aromatic hydrocarbons (PAHs) containing three to five benzene rings were systematically
synthesized by the Pd(II)-catalyzed Friedel–Crafts-type cyclization of 1,1,2-trifluoro- and 1,1-difluoro-1-alkenes and the
In(III)-catalyzed tandem cyclization of bis(1,1-difluoroallene)s. Using an array of the difluorinated PAHs that were obtained
and previously reported monofluorinated PAHs, the physical properties of the pinpoint-fluorinated PAHs were investigated.
(i) The 19F NMR signals of the bay-region fluorine atoms were shifted downfield by ca. 8–14 ppm for vic-difluorinated PAHs
and ca. 11–19 ppm for non-vic-difluorinated and monofluorinated PAHs. (ii) The introduction of fluorine into PAH
molecules increased their solubilities in organic solvents, which was best exemplified by the high solubilities of 6,7-
difluoropicene (5.4 wt%) and 6-fluoropicene (5.3 wt%) in THF. (iii) The HOMO–LUMO energy gaps of the pinpoint-

2
fluorinated PAHs were smaller than that of the corresponding fluorine-free PAH (i.e., picene) by 0.02–0.26 eV, and the
HOMO and LUMO energy levels were lowered by 0.10–0.22 eV and 0.12–0.41 eV, respectively.
Highlights

Difluorinated PAHs were synthesized by the cyclization of fluoroalkenes or -allenes with a Pd(II)- or an In(III)
catalyst.> The 19F NMR signals of the bay fluorines were shifted downfield by 8–14 ppm (vic-difluoro) and 11–19
ppm (non-vic-difluoro).> The fluorine introduction into PAHs increased their solubilities, exemplified by that of 6,7-
difluoropicene (5.4 wt%) in THF.> The HOMO–LUMO energy gaps of fluorinated PAHs were smaller than that of
the corresponding fluorine-free PAH by 0.02–0.26 eV.> The HOMO energy levels of fluorinated PAHs were
lowered by 0.10–0.22 eV, suggesting their resistance to aerial oxidation.
ABSTRACT: Difluorinated polycyclic aromatic hydrocarbons (PAHs) containing three to five benzene
rings were systematically synthesized by the Pd(II)-catalyzed Friedel–Crafts-type cyclization of 1,1,2-
trifluoro- and 1,1-difluoro-1-alkenes and the In(III)-catalyzed tandem cyclization of bis(1,1-
difluoroallene)s. Using an array of the difluorinated PAHs that were obtained and previously reported
monofluorinated PAHs, the physical properties of the pinpoint-fluorinated PAHs were investigated. (i)
The 19F NMR signals of the bay-region fluorine atoms were shifted downfield by ca. 8–14 ppm for vic-
difluorinated PAHs and ca. 11–19 ppm for non-vic-difluorinated and monofluorinated PAHs. (ii) The
introduction of fluorine into PAH molecules increased their solubilities in organic solvents, which was
best exemplified by the high solubilities of 6,7-difluoropicene (5.4 wt%) and 6-fluoropicene (5.3 wt%)
in THF. (iii) The HOMO–LUMO energy gaps of the pinpoint-fluorinated PAHs were smaller than that
of the corresponding fluorine-free PAH (i.e., picene) by 0.02–0.26 eV, and the HOMO and LUMO
energy levels were lowered by 0.10–0.22 eV and 0.12–0.41 eV, respectively.
KEYWORDS:
Cyclization, Fluoroalkenes, Fluoroallenes, Polycyclic aromatic hydrocarbons, Solubility,
Semiconductors
1. Introduction
Polycyclic aromatic hydrocarbons (PAHs) are compounds that comprise ortho- and/or peri-fused
benzene rings in various configurations [1]. Acenes and phenacenes are representatives of this class of
molecules with a linear and zigzag configuration, respectively. Importance of these PAHs as organic

3
semiconducting materials is increasing significantly in the field of materials science [2]. Therefore, the
development of methods for the synthesis of PAHs is becoming an important issue.
Regioselectively mono- or difluorinated (pinpoint-fluorinated) PAHs (F-PAHs, Figure 1) are a
promising class of organic semiconducting materials because of the unique properties of the fluorine
substituent(s) (Figure 2) [3]: (a) The high electronegativity of fluorine leads to an increase in the
resistance of the fluorinated PAHs to aerial oxidation by lowering the energy levels of their HOMO. (b)
The repulsive interaction between the lone pairs in the fluorine 2p orbitals and the adjacent -electrons
in the carbon 2p orbitals perturbs the electron distribution in the extended -system [4]. The induced
polarization renders PAHs highly soluble in polar solvents, leading to printable organic electronic
devices [5]. (c) From the viewpoint of steric bulk, the low steric demand of fluorine, the introduction of
which into PAHs causes no significant change in their molecular shape, would have little effect on their
- stacking in the solid state. Thus, the electronic and steric effects of attaching single or double
fluorine substituent(s) to PAH skeletons can endow them with advantageous semiconducting properties,
as exemplified by fluorinated picenes, which are soluble in THF and exhibit p-type semiconducting
behavior [6,7].
Figure 1. Structures of pinpoint-fluorinated acenes and phenacenes (n refers to
the number of benzene rings).

4
Figure 2. Electronic and steric effects of a fluorine substituent on an adjacent 
system.
In spite of their potential, however, studies of pinpoint-fluorinated PAHs have been hampered by
the lack of available methods for their systematic synthesis [8]. Synthetic approaches to fluorinated
aromatic compounds are broadly classified into two categories: (i) strategies for the introduction of
fluorine (Scheme 1) and (ii) strategies for the construction of fluorinated rings. Although the
regioselective introduction of fluorine into aromatic systems has been studied for a long time [9], it has
drawbacks, namely, the need for the prior regioselective introduction of a functional group (a) or a
directing group (b) to control the regioselectivity of the reaction, as well as the construction of the PAH
skeleton. In spite of its efficiency, the construction of fluorinated aromatic rings has been limited to the
oxidative photocyclization or the coupling reaction of cis-stilbene derivatives [10].
Scheme 1. Strategies for the Introduction of fluorine to form fluoroarenes (FG =
functional group; DG = directing group).
By means of the latter strategy, we have reported the synthesis of pinpoint-fluorinated phenacenes
by the cyclization of 1,1-difluoro-1-alkenes catalyzed by cationic Pd(II) species (Figure 3) [6]. 1,1-
Difluoroalkenes 1, possessing an o-biphenyl skeleton were treated with a catalytic amount of
[Pd(MeCN)4](BF4)2 or PdCl2/AgOTf (1:2) in the presence of boron trifluoride etherate (1.0 equiv) in
1,1,1,3,3,3-hexafluoropropan-2-ol [11]. Pinpoint-monofluorinated chrysenes ([4]phenacenes) 2a and 2b
and picenes ([5]phenacenes) 2c–e were synthesized in good yields, although difluorinated PAHs have
not yet been synthesized by this protocol.

5
Figure 3. Strategy for the construction of fluorinated rings to form fluoroarenes:
electrophilic activation of 1,1-difluoro-1-alkenes (synthesis of pinpoint-
monofluorinated phenacenes).
In this paper, the syntheses of pinpoint-difluorinated PAHs involving the Pd(II)-catalyzed Friedel–
Crafts-type cyclization of 1,1,2-trifluoro- and 1,1-difluoro-1-alkenes and the In(III)-catalyzed Friedel–
Crafts-type cyclization of 1,1-difluoroallenes are described. The assembly of an array of difluorinated
PAHs formed via these protocols and previously reported monofluorinated PAHs, which mainly
comprised phenacenes, enabled studies of their physical properties such as solubility, downfield shift in
19F NMR spectroscopy, and HOMO/LUMO energy gap.
2. Results and discussion
2.1. Synthesis of vic-difluorinated PAHs
Although vic-difluorinated aromatic compounds constitute an attractive subfamily of pinpoint-
fluorinated PAHs, their selective synthesis has been rare [12]. We envisioned that the employment of
1,1,2-trifluoro-1-alkenes as substrates for the aforementioned electrophilic cyclization (Friedel–Crafts-
type cyclization) would enable the facile construction of vic-difluorinated PAHs.
2.1.1. Preparation of 1,1,2-trifluoro-1-alkenes

6
The required 1,1,2-trifluoro-1-alkenes were prepared by the Negishi coupling of a
trifluorovinylzinc(II) complex with the corresponding aryl triflates or iodides [13]: Trifluorovinyllithium,
which was generated from commercially available 1,1,1,2-tetrafluoroethane and LDA (2.0 equiv), was
treated with zinc dichloride in the presence of TMEDA at –78 °C (Scheme 2). 19F NMR analysis
indicated that trifluorovinylzinc(II) chloride–TMEDA complex 3 (65% yield based on ZnCl2) was
obtained along with an inseparable bis(trifluorovinyl)zinc complex (16% yield).

7
Scheme 2. Preparation of trifluorovinylzinc(II) complex 3.
The Negishi coupling of trifluorovinylzinc(II) complex 3 afforded the required 1,1,2-trifluoro-1-
alkenes (Table 1). Trifluoroalkene 5a, which bears a biphenyl moiety, was prepared from 3 and
commercially available 2-iodo-1,1'-biphenyl in 98% yield (Entry 1). Aryl triflates 4b and 4c afforded the
corresponding products 5b and 5c in 94% and 68% yields, respectively, using a 1,3-
bis(diphenylphosphino)propane (dppp) ligand (Entries 2–5). The coupling of triflates 4d and 4e
proceeded smoothly to afford 5d and 5e in 27% and 85% yields, respectively (Entries 6,7).

8
Table 1. Preparation of 1,1,2-trifluoro-1-alkenes.
Entry
1
Triflate (Iodide)
Trifluoroalkene
x
2
t (h)
Yield (%) a
98
5a
18
2
4b
4b
5b
5b
10
8
11
24
8 b
94
3 c
4
4c
4c
5c
5c
10
5
19
7
20 b
68
5 c
6
7
4d
4e
5d
5e
10
10
25
13
27
85
b
c
a 19F NMR yield based on PhCF3 as an internal standard. Isolated yield. Instead of PPh3, dppp (2x mol%) was
used. dba = benzylideneacetone.
2.1.2. Electrophilic cyclization of 1,1,2-trifluoro-1-alkenes
Having synthesized the required trifluoroalkenes, the Pd(II)-catalyzed electrophilic cyclization
was examined (Table 2). The cyclization of trifluoroalkene 5a proceeded under catalysis by
PdCl2/AgOTf [6a] to afford 9,10-difluorophenanthrene (6a) in 47% yield (Entry 1). Cyclization on the
naphthalene moiety in 5b proceeded to afford the product as a single isomer (51% yield, Entry 2). A 19F
NMR study of the obtained product suggested that 5,6-difluorochrysene (6b) was obtained (vide infra).
Thus, the cyclization reaction took place at the -position of the naphthalene substructure, and the same
regioselectivity was observed as in the cyclization of 1,1-difluoro-1-alkenes [6a]. The PdCl2/AgNTf2

9
catalytic system was effective for increasing the yield of 6. vic-Difluorinated chrysene 6b and picenes
6c/6c' were synthesized from trifluoroalkenes 5b and 5c in 78% and 63% yields, respectively (Entries
3–5). As shown in Entry 6, it was revealed that cyclization on a benzene moiety was slower than on a
naphthalene moiety. Phenylated trifluoroalkene 5d afforded 5,6-difluorochrysene (6b) albeit only in
18% yield, which was much lower than that obtained by the reaction of naphthylated trifluoroalkene 5b
(78% yield, Entry 3). In other words, vic-difluorinated phenacenes were synthesized in greater yields by
cyclization on a naphthalene or phenanthrene moiety rather than on a benzene moiety. The cyclization of
trifluoroalkene 5e successfully afforded difluorinated picene 6e in 98% yield (Entry 8). The
regiochemistry observed in the cyclization of 5b, 5c, and 5e can be explained by a Friedel–Crafts-type
mechanism (vide infra). Thus, it stems from the high reactivity of the α carbon of naphthalene and the
C1 carbon of phenanthrene toward electrophilic aromatic substitution.

10
Table 2. Synthesis of vic-difluorophenacenes by electrophilic cyclization of 1,1,2-trifluoro-1-alkenes. a
Entry
1
Trifluoroalkene
AgX
t (h)
Difluorophenacene
Yield (%)
47
5a
AgOTf
2
6a
2
3
5b AgOTf
5b AgNTf2
2
2
6b
6b
51 a
78
4
5
5c
AgOTf
2.5
2
6c
6c
27 a,b
5c AgNTf2
72
(6c : 6c' = 88 : 12) a
63
(6c : 6c' = 89 : 11)
6
5d AgNTf2
2
6b
18 a
7
8
5e
AgOTf
1.3
1.3
6e
6e
75 a
98
5e AgNTf2
a 19F NMR yield based on PhCF3 as an internal standard. b A small amount of 6c' was observed by 19F NMR
spectroscopy. Tf = trifluoromethanesulfonyl.
Electrophilic cyclization was also conducted in a gram-scale operation (Scheme 3).
Trifluoroalkene 5e (2.06 g) underwent cyclization in the presence of a PdCl2/AgNTf2 catalyst (20 mol%)
to afford crude 13,14-difluoropicene (6e). Sublimation (200 °C, 2.3 mmHg, four cycles) gave pure 6e in
the form of yellow needles (1.04 g; 54% yield).

11
Scheme 3. Gram-scale synthesis of 13,14-difluoropicene (6e).
2.1.3. Catalytic cycle
A mechanism of the cyclization of 1,1,2-trifluoro-1-alkenes 5 is proposed in Scheme 4.
Trifluoroalkenes 5 coordinate to the cationic palladium(II) center to form -complexes A, in which the
electron density of the trifluoroalkene moiety is lowered. This electrophilic activation promotes a
Friedel–Crafts-type ring closure to provide cyclic alkylpalladium(II) intermediates B, which in turn
undergo the BF3-assisted -fluorine elimination to yield vic-difluorinated phenacenes 6. The formation
–
of BF4 ion regenerates the active cationic palladium(II) species.
Scheme 4. Plausible mechanism for cyclization of trifluoroalkenes 5 (L = solvent).
2.2. Synthesis of other difluorinated PAHs
As well as vic-difluorinated phenacenes, other difluorophenacenes and related F-PAHs were
synthesized by the cyclization of 1,1-difluoro-1-alkenes bearing a fluorophenyl group (Scheme 5). 1,1-

12
Difluoro-1-alkenes 1f and 1g, which bear an additional fluorine substituent on one of their aromatic
rings, underwent cyclization under catalysis by cationic palladium(II) species to afford the
corresponding difluoropicenes 6f/6f' and 6g/6g' in 47% and 68% yields, respectively.
Scheme 5. Synthesis of pinpoint-difluorinated picenes by electrophilic cyclization
of 1,1-difluoro-1-alkenes.
Our established protocol for the cyclization/ring expansion of 1,1-difluoroallenes [14] was
conducted in a tandem fashion to afford the desired non-vic-difluorinated PAHs. When bis(1,1-
difluoroallene) 7a, which was readily prepared from p-xylene, was subjected to catalysis by InBr3, 6,7-
difluoropicene
(6h) was obtained as a single isomer in 75% yield (Scheme 6a). The
dihydrophenanthrene intermediate generated in situ underwent a second cyclization reaction at the -
position of the newly formed naphthalene substructure, followed by one-pot dehydrogenation by DDQ

13
to give 6h. Bis(1,1-difluoroallene) 7b, which was prepared from m-xylene, also underwent tandem
cyclization in a similar manner to afford difluorobenzanthracene 6i as a single isomer in 76% yield
(Scheme 6b). Severe steric repulsion probably promoted cyclization at the electronically less reactive -
position of the naphthalene substructure.
Scheme 6. Synthesis of pinpoint-difluorinated PAHs by tandem electrophilic
cyclization of bis(1,1-difluoroallene)s.
2.3. Planarity of pinpoint-fluorinated PAHs
Because of the low bulk of fluorine, in the same way as the reported monofluorinated 2a, 2b, 2d,
and 2e, [6a] the pinpoint-difluorinated PAHs have planar structures (Figure 4). Single crystal X-ray
structure analysis of 5,6-difluoropicene (6c, CCDC 1563733) indicated that this molecule has a C6–
C6a–C6b–C7 torsion angle of 0.18°, which is smaller than that observed in the parent picene (1.96°,
CCDC 991788). 1,6-Difluoropicene (6f, CCDC 1547302) has C1–C13b–C13a–C13 and C6–C6a–C6b–

14
C7 torsion angles of 1.84° and 1.31°, respectively, which are similar to those in picene. These facts
suggest that the planarity of the pinpoint-fluorinated PAHs was not affected by the introduction of
fluorine [15]. As an exception, 6,7-difluoropicene (6h, CCDC 1545329) has a large C6–C6a–C6b–C7
torsion angle (26.9°), which is ascribed to the repulsive interaction between the two fluorine atoms.
Figure 4. ORTEP diagrams of pinpoint-difluorinated picenes.

15
2.4. Downfield shift in 19F NMR signals of bay-region fluorine atoms
Chemical shifts in 19F NMR spectroscopy are important parameters for characterizing the structures
19
of fluorine-containing molecules. For the F-PAHs, the F NMR signals of bay-region fluorine atoms
were found to undergo a drastic downfield shift in comparison with those of non-bay-region (K-region,
Figure 5) [1a,b] fluorine atoms.
Figure 5. Bay- and K-regions of PAHs.
Single crystal X-ray structure analysis confirmed that 6-fluorochrysene (2b, CCDC 911876) [6a],
a substituted 9-fluorophenanthrene (2f, CCDC 1058043) [6b], and 6-fluorodibenz[a,h]anthracene (2g,
19
CCDC 978889) [6a] exhibited F NMR signals at 38.4, 37.4, and 37.0 ppm, respectively (vs. C6F6,
19
Figure 6) [16]. 9-Fluorophenanthrene also exhibited a F NMR signal at 37.9 ppm [17]. Thus, the
signals of fluorine atoms located in the K-region were normally observed at 37–40 ppm (upfield region).
1-Fluoronaphthalene also exhibited a 19F NMR signal in this region (39.1 ppm) [18].
In contrast, 5-fluorochrysene (2a, CCDC 911785) [6a], 6-fluoropicene (2d, CCDC 978888) [6a],
13-fluoropicene (2e, CCDC 957306) [6a], 1,6-difluoropicene (6f, CCDC 1547302), and 6,7-
difluoropicene (6h, CCDC 1545329), in which the fluorine atoms are located in bay regions, exhibited
19F NMR signals in the range of 50–56 ppm (downfield region).

16
Figure 6. Colored: Structures and 19F NMR chemical shifts (vs. C6F6) of F-PAHs, of which the
structures were determined by single crystal X-ray structure analysis. Uncolored: Structures
and chemical shifts (vs. C6F6) of F-PAHs in the literature.
19
It must be emphasized that the chemical shifts of the F NMR signals for pinpoint-fluorinated
PAHs 2c [6a], 6g, and 6i were fully consistent with the rule described above (Figure 7). Therefore, their
structures were determined not by single crystal X-ray structure analysis but by 19F NMR. 5-
Fluoropicene (2c) and difluorinated dibenzanthracene 6i have fluorine substituents in the non-bay (K)
region, of which the signals were observed in the upfield region (40.2 ppm for 2c and37.2 ppm for 6i).
Difluoropicene 6g has a bay-region fluorine substituent (C6), of which the signal appeared as a doublet
(JFH = 16 Hz) in the downfield region (54.5 ppm). Although the non-bay-region fluorine atom of 6g (C3)
exhibited a signal that was apparently in the downfield region (49.5 ppm, dd), this was an acceptable
value because the similar fluorine atom in 2-fluorophenanthrene exhibited a signal at 47.1 ppm [19].

17
Figure 7. Structures and 19F NMR assignments of 2c, 6g, and 6i (vs. C6F6).
NMR signals of fluorine atoms in vic-difluorinated phenacenes appeared in distinct 21–24 ppm
(downfield) and 10–13 ppm (upfield) regions (Table 3). 9,10-Difluorophenanthrene (6a), in which both
19
fluorine atoms are in the non-bay (K) region, exhibited a F NMR signal in the upfield region (10.4
ppm). On the other hand, 13,14-difluoropicene (6e), in which both fluorine atoms are in the bay region,
19
exhibited a F NMR signal in the downfield region (23.9 ppm). 5,6-Difluorochrysene (6b) and 5,6-
difluoropicene (6c, CCDC 1563733), which both have one bay-region fluorine atom and one non-bay-
region (K) fluorine atom, exhibited signals in both the downfield region (21.6 ppm for 6b and 22.0 ppm
for 6c) and the upfield region (12.6 ppm for 6b and 13.0 ppm for 6c). On the basis of these observations,
19F NMR signals of vic-difluorinated PAHs are observed in both downfield and upfield regions, and can
reasonably be assigned to bay-region and non-bay-region (K) fluorine atoms, respectively.

18
Table 3. 19F NMR chemical shifts (vs. C6F6) and assignments of vic-difluorinated phenacenes. a
Downfield region
Upfield region
Compounds
( 21–24)
( 10–13)
10.4
(K, C9, C10)
6a
6e
23.9
(bay, C13, C14)
21.6 (bay, C5)
22.0 (bay, C6)
12.6 (K, C6)
13.0 (K, C5)
6b
6c
a Colored: Structure determined by single crystal X-ray structure analysis.
The abovementioned downfield shifts were apparently due to the deshielding effect of the opposite
benzene ring in the bay region, whereas systematic study on the deshielding effect has not been reported
till date [10i]. In the array of synthesized pinpoint-fluorinated PAHs, a downfield shift was observed in
19
all the F NMR signals of bay-region fluorine atoms. The magnitudes of the downfield shifts were ca.
11–19 ppm for the monofluorinated and the non-vic-difluorinated PAHs and ca. 8–14 ppm for the vic-
difluorinated PAHs.
2.5. Polarity, solubility, and mobility of pinpoint-fluorinated picenes
A fluorine substituent has an electron-withdrawing inductive effect, and its lone pairs are involved
in a repulsive interaction with the adjacent -electrons (Figure 2), which leads to the polarization of the
molecule. In fact, theoretical calculations indicated that polarity was induced in the phenacene
molecules (Table 4). For example, the dipole moments of 5- and 6-fluoropicenes are 1.37 and 1.28 D
(Entries 2 and 3), respectively, whereas picene has a dipole moment of 0.06 D (Entry 1). Thus, the
introduction of fluorine substituent(s) effectively induced the polarization of the PAH molecules.

19
Wet processes (solution processes) are promising methods that enable the low-cost and easy
fabrication of electronic devices and are characteristically employed with organic materials. For the
adoption of these processes, the solubility of semiconducting materials in organic solvents is an
important factor. Recently, we reported on the solubilizing effect of the introduction of the fluorine
atoms into aromatic systems. However, no systematic study of this effect has been conducted to date
[6a]. We therefore investigated the solubilities of the pinpoint-fluorinated PAHs.
The solubilities of the pinpoint-fluorinated picenes and picene in THF were measured via the
Lambert–Beer law, using a UV–vis spectrometer. Among the monofluorinated picenes, 6-fluoropicene
exhibited high solubility in THF (2d, 0.16 mol/L, 5.3 wt%, Entry 3), which represents a 25-fold increase
in comparison with picene (Entry 1). 13-Fluoropicene also exhibited high solubility (2e, 15-fold increase
with respect to picene, Entry 4). Among the difluorinated picenes, 1,6-difluoropicene (6f, 0.081 mol/L,
2.9 wt%, Entry 7) exhibited comparable solubility to 13-fluoropicene (2e, Entry 4), which was 13 times
that of picene. 6,7-Difluoropicene also exhibited high solubility (6h, 0.15 mol/L, 5.4 wt%, Entry 9). It is
noteworthy that 5-fluoropicene (2c) exhibited p-type semiconducting behavior (mobility 2.81 × 10–5
cm2/Vs) [20].

20
Table 4. Solubility of pinpoint-fluorinated picenes in THF.
max
 at max
Solubility
Dipole moment
(debye), (°)
0.06, 90
Entry
Compound

(nm) (105 L/mol cm) (10–2 mol/L) a (wt%)
1
2
3
4
5
6
7
8
9
picene
–
285
285
287
282
287
282
286
285
290
1.02
1.03
1.07
0.66
1.24
1.25
1.16
1.10
0.98
0.64 (1) [6a]
1.4 (2) [6a]
16 (25) [6a]
9.3 (15) [6a]
3.9 (6)
0.20
0.48
5.3
5-fluoropicene
6-fluoropicene
13-fluoropicene
5,6-difluoropicene
2c
2d
2e
6c
1.37, 69
1.28, 102
1.14, –113
2.40, 84
3.1
1.4
13,14-difluoropicene 6e
2.8 (4)
0.98
2.9
2.07, –90
0.55, 165
1.85, 42
1,6-difluoropicene
3,6-difluoropicene
6,7-difluoropicene
6f
6g
6h
8.1 (13)
5.0 (8)
1.8
15 (23)
5.4
2.54, 90
a The relative solubility is indicated in parentheses.
The introduction of fluorine substituents into organic molecules has been practiced for a long time
in the life sciences [3d]. Fluorine substituents often improve the bioactivity of the original molecule
because of their electronic effects and low steric demand. Our study clearly demonstrated that the
introduction of one or two fluorine atoms into PAHs had an advantageous effect on their solubility
without affecting their planarity, which is of particular interest in materials science [21].
2.6. HOMO and LUMO energy levels of pinpoint-fluorinated picenes
The energy levels of molecules are important factors in the development of electronic devices with
high carrier mobility. In addition, the HOMO energy level is a key parameter used to estimate the
resistance of materials to aerial oxidation. Thus, the HOMO and LUMO energy levels were
systematically investigated for the pinpoint-fluorinated picenes that we synthesized.

21
The energy levels of the pinpoint-fluorinated picenes are listed in Table 5. The energy gaps (Egs)
of the pinpoint-fluorinated picenes and picene were determined on the basis of the longest absorption
wavelength (offset). Picene (i.e., [5]phenacene) exhibited an energy gap of 3.71 eV (Entry 1), which was
smaller than that of chrysene (i.e.; [4]phenacene, 3.8 eV) [22]. Pinpoint-fluorinated picenes 2c–e, 6c,
and 6e–g exhibited Eg values of 3.61–3.69 eV (Entries 2–8), which displayed correlations with those
calculated by DFT (B3LYP/6–31G*, Figure 8). 6,7-Difluoropicene (6h) exhibited the lowest Eg value of
3.45 eV (Entry 9). The introduction of fluorine thus lowered the energy gaps of the picenes.
The reduction peaks of the pinpoint-fluorinated picenes were not definite in cyclic
voltammograms (CV). The HOMO and LUMO energy levels of these compounds were therefore
determined by differential pulse voltammetry (DPV). The oxidation peak (EOX) observed in the
corresponding deferential pulse voltammogram indicated that picene has a deeper HOMO level (–5.62
eV, Entry 1) than pentacene (–5.1 eV) and TIPS-pentacene (–5.1 eV) [23]. The HOMO levels of the
pinpoint-fluorinated picenes, which were estimated in a similar manner, range from –5.72 to –5.84 eV
(Entries 2–9). Substitution by fluorine thus lowered the HOMO levels of the picenes by 0.10–0.22 eV.
These observations are consistent with the fact that the HOMO levels of picene and 13-fluoropicene (2e),
estimated by ultraviolet photoelectron spectroscopy (UPS), are –5.3 eV and –5.4 eV, respectively
(Entries 1 and 4). The deeper HOMO levels of the pinpoint-fluorinated picenes contribute to the high
resistance of these compounds to aerial oxidation.
Reduction peaks could not be found in the differential pulse voltammograms because of overlaps
with the solvent signals. The LUMO levels of the pinpoint-fluorinated picenes were therefore
determined by the equation ELUMO = EHOMO + Eg. The LUMO energy levels of the fluorinated picenes
range from –2.32 to –2.03 eV, which are lower than that of picene (–1.91 eV) by 0.12–0.41 eV.

22
Table 5. HOMO and LUMO energy levels of pinpoint-fluorinated picenes.

offset

Eg
ELUMO – EHOMO
EOX
(V) c
0.82
EHOMO
(eV) d,e
ELUMO
(eV) e,f
–1.91
Entry
1
Compound
picene
(nm) (eV) a (eV, calcd.) b
–
335
336
342
338
3.71
3.69
3.63
3.68
4.22
4.20
4.11
4.13
–5.62
–5.3 g
2
3
4
5-fluoropicene
6-fluoropicene
13-fluoropicene
2c
2d
2e
0.92
0.92
0.95
–5.72
–2.03
(–0.10)
(–0.12)
–5.72
–2.09
(–0.10)
(–0.18)
–5.75
–2.07
(–0.13)
–5.4 g
(–0.16)
5
6
7
8
9
5,6-difluoropicene
6c
341
342
344
340
360
3.65
3.63
3.61
3.65
3.45
4.09
4.07
4.07
4.11
4.01
0.96
1.01
1.04
0.98
0.97
–5.76
–2.12
(–0.14)
(–0.21)
13,14-difluoropicene 6e
–5.81
–2.18
(–0.19)
(–0.27)
1,6-difluoropicene
3,6-difluoropicene
6,7-difluoropicene
6f
6g
6h
–5.84
–2.23
(–0.22)
(–0.32)
–5.78
–2.13
(–0.16)
(–0.22)
–5.77
–2.32
(–0.15)
(–0.41)
a Eg / eV = 1240 / (offset / nm). b Calculated using the B3LYP/6–31G* basis set. c Working/counter electrodes: Pt,
d
e
reference electrode: Ag/Ag+, n-Bu4N ClO4, vs. Fc/Fc+. EHOMO / eV = –4.80 – EOX / eV. The decrease with
respect to picene is indicated in parentheses. f ELUMO = EHOMO + Eg. g Based on the ionization potential determined
by UPS measurements [6a].

23
Figure 8. Comparison of the observed and calculated energy gaps of the pinpoint-
fluorinated picenes and picene.
3. Conclusions
An array of pinpoint-fluorinated PAHs was successfully prepared by the electrophilic cyclization
of 1,1,2-trifluoro-1-alkenes or 1,1-difluoro-1-alkenes catalyzed by cationic Pd(II) species or by the
In(III)-catalyzed tandem cyclization of bis(1,1-difluoroallene)s. We thus, gained a broader perspective
on their physical properties. (i) Single crystal X-ray structure analysis and 19F NMR spectroscopy
showed that the NMR signals of the bay-region fluorine atoms shifted downfield by ca. 11–19 ppm
(monofluorinated and non-vic-difluorinated PAHs) or by ca. 8–14 ppm (vic-difluorinated PAHs). (ii) A
study of the solubility revealed that the introduction of fluorine into PAH molecules solubilizes them in
organic solvents, and 6-fluoropicene and 6,7-difluoropicene exhibited the highest solubilities in THF (5.3
and 5.4 wt%). In addition, 5-fluoropicene exhibited p-type semiconducting behavior (2.81 × 10–5
cm2/Vs). (iii) UV–vis spectroscopy and DPV indicated that the energy gaps (Egs) of the pinpoint-
fluorinated PAHs are smaller (3.61–3.69 eV) than that of the fluorine-free PAH (i.e., picene) and that
the HOMO (–5.72 to –5.84 eV) and LUMO (–2.32 to –2.03 eV) energy levels of the pinpoint-
fluorinated picenes were lowered by 0.10–0.22 eV and 0.12–0.41 eV, respectively.

24
4. Experimental
4.1. General information
IR spectra were recorded on a Horiba FT-300S spectrometer. NMR spectra were recorded on a
Bruker Avance 500 spectrometer in CDCl3, at 500 MHz (1H NMR), at 126 MHz (13C NMR), and at 470
MHz (19F NMR). Chemical shift values were given in ppm relative to internal Me4Si (for 1H NMR: 
19
0.00), CDCl3 (for 13C NMR: = 77.0), and C6F6 (for F NMR:  = 0.0) [16]. Mass spectra were taken
with Jeol JMS-T100GCV (EI, 70 eV) or JMS-T100CS (APCI+) spectrometers. UV–Vis absorption
spectra were determined using a Jasco V-630 spectrometer. Cyclic and differential pulse
voltammograms were recorded with a BAS ALS 600Bz analyser. Elemental analyses were performed
with a Yanako MT-3 CHN Corder apparatus. Mobility was measured using a Keysight 4156C
semiconductor parameter analyser.
4.2. Synthesis of vic-difluorinated PAHs
4.2.1. Preparation of 1,2,2-trifluorovinylzinc(II) chloride–TMEDA (1/1) (3)
Trifluorovinylzinc(II) chloride–TMEDA complex was prepared by the method in the literature but
at –78 °C [13c]. To a THF solution (7 mL) of 1,1,1,2-tetrafluoroethane [gas (300 mL) was condensed at
–78 °C, 13.5 mmol] and TMEDA (2.20 mL, 14.7 mmol) was slowly added a THF solution (11 mL) of
lithium diisopropylamide (LDA, 22.6 mmol) at –78 °C over 20 min. A THF solution (7 mL) of
anhydrous ZnCl2 (1.6 mol/L, 11.2 mmol) [24] was added to the reaction mixture at –78 °C. After stirring
19
at –78 °C for 2 h, the reaction mixture was slowly warmed to room temperature. F NMR analysis of
the colorless solution, using PhCF3 as an internal standard, indicated that the desired
trifluorovinylzinc(II)–TMEDA complex 3 was generated in 65% yield, along with 16% yield of
divinylzinc(II) complex. This solution was kept in a refrigerator (–35 °C) without substantial
decomposition over one month.
4.2.2. Preparation of biaryl triflates 4
Biaryl triflate 4d was prepared from phenylboronic acid and 2-bromo-1-
trifluoromethanesulfonyloxynaphthalene under Pd catalysis [6a]. Other biaryl triflates were prepared

25
from the corresponding boronic acids and bromotriflates by a similar procedure. Specifically,
phenanthren-2-ylboronic acid for 4c was prepared from 2-bromophenanthrene [25] (n-BuLi 1.1 equiv,
THF, –90 °C; B(OMe)3 2.5 equiv, RT; aq. HCl, 98% yield).
4.2.3. Spectral data of biaryl triflates 4
4.2.3.1. 2-(2-Naphthyl)phenyl trifluoromethanesulfonate (4b)
1H NMR (500 MHz, CDCl3): δ 7.29–7.35 (m, 3H), 7.38–7.43 (m, 2H), 7.44–7.49 (m, 2H), 7.74–7.79 (m,
2H), 7.81 (d, J = 8.5 Hz, 1H), 7.84 (s, 1H); 13C NMR (126 MHz, CDCl3): 118.3 (q, JCF = 321 Hz), 122.1,
126.4, 126.6, 126.9, 127.7, 128.15, 128.19, 128.5, 128.7, 129.0, 132.2, 132.8, 133.0, 133.2, 135.4,
19
146.9; F NMR (470 MHz, CDCl3): δ 88.9 (s); IR (neat): ν~ 1419, 1203, 1136, 1093, 887, 729, 596
cm–1; HRMS (70 eV, EI): m/z calcd. for C17H11F3O3S ([M]+): 352.0381; found: 352.0373.
4.2.3.2. 2-(Phenanthren-2-yl)phenyl trifluoromethanesulfonate (4c)
1H NMR (500 MHz, CDCl3): δ 7.42–7.51 (m, 3H), 7.59–7.64 (m, 2H), 7.67 (ddd, J = 7.1, 7.0, 1.5 Hz,
1H), 7.75 (d, J = 8.6, 2.0 Hz, 1H), 7.76 (d, J = 8.9 Hz, 1H), 7.78 (d, J = 9.0 Hz, 1H), 7.90 (dd, J = 7.9,
1.2 Hz, 1H), 7.99 (d, J = 1.9 Hz, 1H), 8.70 (d, J = 8.2 Hz, 1H), 8.75 (d, J = 8.6 Hz, 1H); 13C NMR (126
MHz, CDCl3): 118.3 (q, JCF = 321 Hz), 122.2, 122.8, 123.0, 126.79, 126.87, 126.92, 127.5, 127.6,
19
128.61, 128.63, 129.1, 129.3, 130.0, 132.0, 132.25, 132.31, 133.7, 135.2, 146.9; F NMR (470 MHz,
CDCl3): δ 88.3 (s); IR (neat): ν~ 1419, 1207, 1138, 906, 879, 742, 600 cm–1; HRMS (70 eV, EI): m/z
calcd. for C21H13F3O3S ([M]+): 402.0537; found: 402.0532.
4.2.3.3. 2-(2-Naphthyl)naphthalen-1-yl trifluoromethanesulfonate (4e)
1H NMR (500 MHz, CDCl3):  7.53–7.57 (m, 2H), 7.61–7.69 (m, 3H), 7.71 (ddd, J = 8.3, 7.0, 1.2 Hz,
13
1H), 7.89–7.94 (m, 2H), 7.94–7.99 (m, 3H), 8.05 (d, J = 1.5 Hz, 1H), 8.22 (d, J = 8.5 Hz, 1H); C
NMR (126 MHz, CDCl3):  118.1 (q, JCF = 320 Hz), 121.7, 126.5, 126.7, 127.21, 127.24, 127.5, 127.8,
128.0, 128.1, 128.2, 128.3, 128.6, 128.7, 129.2, 132.7, 132.9, 133.3, 133.7, 134.1, 142.1; 19F NMR (470
MHz, CDCl3):  87.7 (s); IR (neat): ~ 3059, 1415, 1209, 1134, 816, 744 cm–1; EA: calcd. for
C21H13F3O3S: C 62.68%, H 3.26%; found: C 63.03%, H 3.25%.

26
4.2.4. Negishi-coupling of trifluorovinylzinc(II) chloride–TMEDA complex 3 with aryl iodides or
triflates
4.2.4.1. Synthesis of 1,1,2-trifluoro-1-alkene 5a
The reagent loading of 3 for the Negishi coupling was calculated on the basis of the concentration of 3
19
determined by F NMR. Although the bis(trifluorovinyl)zinc complex partly took part in the coupling
reaction [26], the amount of the bis(trifluorovinyl)zinc complex was excluded in the preparation of 5.
To a THF solution (150 mL) of trifluorovinylzinc(II) 3 (0.126 mol/L, 18.9 mmol) were added 2-
iodo-1,1'-biphenyl (4.44 g, 15.9 mmol), Pd2(dba)3･CHCl3 (392 mg, 0.378 mmol), and PPh3 (426 mg,
1.61 mmol). The resulting solution was refluxed for 18 h. The reaction mixture was cooled to room
temperature and silica gel was added. After removal of the solvent under reduced pressure, the residue
was purified by column chromatography on silica gel (hexane) to give a dark red oil. This crude product
was purified by Kügel–Rohr distillation to give trifluoroalkene 5a as a colorless liquid (3.65 g, 98%
yield).
4.2.4.2. Synthesis of 1,1,2-trifluoro-1-alkenes 5b–f
Preparation of trifluoroalkene 5b is described as a typical procedure. To a THF solution (83 mL)
of 3 (0.143 mol/L, 11.9 mmol) were added triflate 4b (2.10 g, 5.97 mmol), Pd2(dba)3･CHCl3 (502 mg,
0.485 mmol), and dppp (396 mg, 0.959 mmol). The resulting solution was refluxed for 24 h. The
reaction mixture was cooled to room temperature and silica gel was added. After removal of the solvent
under reduced pressure, the residue was purified by column chromatography on silica gel (hexane) to
give trifluoroalkene 5b as a yellow liquid (1.60 g, 94% yield).
4.2.5. Spectral data of 1,1,2-trifluoro-1-alkenes 5
4.2.5.1. 2-(1,2,2-Trifluoroethenyl)-1,1'-biphenyl (5a)
13
1H NMR (500 MHz, CDCl3): δ 7.35–7.44 (m, 7H), 7.48–7.53 (m, 2H); C NMR (126 MHz, CDCl3):
125.0 (dd, JCF = 20, 4 Hz), 127.4, 127.59, 127.60 (ddd, JCF = 219, 52, 20 Hz), 128.3, 130.4, 130.4, 130.5,
19
130.7, 140.2, 142.7, 152.9 (ddd, JCF = 328, 277, 51 Hz); F NMR (470 MHz, CDCl3): δ 3.77 (dd, J =

27
117, 30 Hz, 1F), 45.3 (dd, J = 117, 74 Hz, 1F), 60.8 (dd, J = 74, 30 Hz, 1F); IR (neat): ν~ 1782, 1284,
1138, 982, 741, 698 cm–1; HRMS (70 eV, EI): m/z calcd. for C14H9F3 ([M]+): 234.0656; found: 234.0656.
4.2.5.2. 1-(2-Naphthyl)-2-(1,2,2-trifluoroethenyl)benzene (5b)
1H NMR (500 MHz, CDCl3): δ 7.46 (dd, J = 7.0, 7.0 Hz, 1H), 7.49–7.57 (m, 6H), 7.83–7.90 (m, 4H);
13C NMR (126 MHz, CDCl3): 125.2 (dd, JCF = 20, 4 Hz), 126.2, 126.3, 126.5, 127.3, 127.4, 127.6 (ddd,
JCF = 233, 52, 20 Hz), 127.7, 128.0, 128.2, 130.5, 130.7 (d, JCF = 2 Hz), 130.8, 132.6, 133.3, 137.7,
142.5, 152.9 (ddd, JCF = 328, 278, 50 Hz); 19F NMR (470 MHz, CDCl3): δ 2.95 (dd, J = 117, 30 Hz, 1F),
44.7 (dd, J = 117, 74 Hz, 1F), 60.2 (dd, J = 74, 30 Hz, 1F); IR (neat): ν~: 1778, 1491, 1284, 1138, 982,
820, 758 cm–1; HRMS (70 eV, EI): m/z calcd. for C18H11F3 ([M]+): 284.0813; found: 284.0806.
4.2.5.3. 1-(Phenanthren-2-yl)-2-(1,2,2-trifluoroethenyl)benzene (5c)
1.19 g, 68% yield, a pall yellow solid; 1H NMR (500 MHz, CDCl3): δ 7.43–7.47 (m, 1H), 7.54–7.57 (m,
3H), 7.60 (dd, J = 7.4, 7.4 Hz, 1H), 7.64–7.69 (m, 2H), 7.74 (d, J = 9.0 Hz, 1H), 7.77 (d, J = 9.0 Hz, 1H),
7.88–7.91 (m, 2H), 8.70 (dd, J = 8.7, 8.7 Hz, 2H); 13C NMR (126 MHz, CDCl3): 122.7, 122.8, 125.2 (dd,
JCF = 20, 5 Hz), 126.7, 126.8, 126.9, 127.4, 127.5, 127.7 (ddd, JCF = 222, 52, 20 Hz), 128.1, 128.6, 129.6,
130.1, 130.5, 130.76, 130.77, 130.83, 132.0, 132.2, 138.4, 142.3, 152.9 (ddd, JCF = 328, 278, 50 Hz); 19F
NMR (470 MHz, CDCl3): δ 3.91 (dd, J = 117, 30 Hz, 1F), 45.6 (dd, J = 117, 74 Hz, 1F), 61.1 (dd, J =74,
30 Hz, 1F); IR (neat): ν~ 1774, 1444, 1281, 1136, 980, 808, 742 cm–1; HRMS (70 eV, EI): m/z calcd. for
C22H13F3 ([M]+): 334.0969; found: 334.0962.
4.2.5.4. 2-Phenyl-1-(1,2,2-trifluoroethenyl)naphthalene (5d)
0.464 g, 27% yield, a yellow liquid. 1H NMR (500 MHz, CDCl3): δ 7.39–7.49 (m, 5H), 7.56 (d, J = 8.3
Hz, 1H), 7.57 (d, J = 6.3 Hz, 1H), 7.64 (ddd, J = 8.2, 7.0, 1.3 Hz, 1H), 7.93 (d, J = 8.2 Hz, 1H), 8.02–
8.06 (m, 2H); 13C NMR (126 MHz, CDCl3): 120.9 (dd, JCF = 19, 4 Hz), 125.0, 125.5 (ddd, JCF = 234, 54,
20 Hz), 126.5, 127.6, 127.7, 127.8, 128.3, 128.9, 131.45, 131.47, 132.55 (d, JCF = 1 Hz), 132.63 (d, JCF
= 3 Hz), 140.3, 143.0, 153.4 (ddd, JCF = 327, 276, 51 Hz); 19F NMR (470 MHz, CDCl3): δ 8.81 (dd, J =
118, 27 Hz, 1F), 46.9 (dd, J = 118, 73 Hz, 1F), 61.0 (dd, J = 73, 27 Hz, 1F); IR (neat): ν~ 1788, 1230,

28
1140, 1099, 947, 762, 702 cm–1; HRMS (70 eV, EI): m/z calcd. for C18H11F3 ([M]+): 284.0813; found:
284.0825.
4.2.5.5. 2-(2-Naphthyl)-1-(1,2,2-trifluoroethenyl)naphthalene (5e)
0.141 g, 85% yield, colorless crystals; 1H NMR (500 MHz, CDCl3): δ 7.54 (d, J = 6.1 Hz, 1H), 7.55 (d,
J = 6.1 Hz, 1H), 7.60 (dd, J = 7.5, 7.5 Hz, 2H), 7.66 (dd, J = 8.2, 8.2 Hz, 2H), 7.89–7.97 (m, 5H), 8.07
(d, J = 8.3 Hz, 2H); 13C NMR (126 MHz, CDCl3): δ 121.1 (dd, JCF = 19, 4 Hz), 125.0, 125.4 (ddd, JCF =
234, 54, 21 Hz), 126.36, 126.38, 126.6, 126.9, 127.5 (d, JCF = 24 Hz), 127.7, 127.8, 127.88, 127.92,
128.0, 128.29, 128.32, 131.5 (d, JCF = 3 Hz), 132.6, 132.7, 133.2, 137.8, 142.8, 153.5 (ddd, JCF = 292,
276, 51 Hz); 19F NMR (470 MHz, CDCl3): δ 8.64 (dd, J = 118, 27 Hz, 1F), 47.0 (dd, J = 118, 72 Hz, 1F),
61.2 (dd, J = 72, 27 Hz, 1F); IR (neat): ν~ 2924, 1790, 1300, 1138, 1095, 820, 746 cm–1; HRMS (70 eV,
EI): m/z calcd. for C22H13F3 ([M]+): 334.0970; found: 334.0969.
4.2.6. Synthesis of vic-difluorinated PAHs 6a–e
Synthesis of 5,6-difluorochrysene (6b) is described as a typical procedure. To a HFIP suspension
(2 mL) of palladium(II) chloride (3.3 mg, 0.019 mmol) were added trifluoroalkene 5b (57 mg, 0.20
mmol), silver bis(trifluoromethanesulfonyl)imide (23 mg, 0.059 mmol), and boron trifluoride etherate
(BF3･OEt2, 25 L, 0.20 mmol) at 0 ℃. After the reaction mixture was stirred for 2 h at 60 ℃, aqueous
sodium hydrogen carbonate was added to quench the reaction. Organic materials were extracted with
dichloromethane four times. The combined extracts were washed with brine and dried over anhydrous
sodium sulfate. After removal of the solvent under reduced pressure, the residue was purified by column
chromatography on silica gel (hexane) to give 5,6-difluorochrysene (6b) as colorless crystals (42 mg,
78% yield).
4.2.7. Spectral data of vic-difluorinated PAHs 6a–e
4.2.7.1. 9,10-Difluorophenanthrene (6a)
0.100 g, 47% yield, a colorless solid; 1H NMR (500 MHz, CDCl3): δ 7.64–7.74 (m, 4H), 8.14–8.20 (m,
13
2H), 8.60–8.67 (m, 2H); C NMR (126 MHz, CDCl3): 120.9 (dd, JCF = 6.5, 6.5 Hz), 122.7, 124.4 (dd,

29
19
JCF = 8.6, 8.6 Hz), 126.8, 127.4, 127.9, 142.2 (dd, JCF = 252, 13 Hz); F NMR (470 MHz, CDCl3): δ
10.4 (s); IR (neat): ν~ 1657, 1356, 1242, 1016, 906, 746, 544 cm–1; HRMS (70 eV, EI): m/z calcd. for
C14H8F2 ([M]+): 214.0594; found: 214.0595.
4.2.7.2. 5,6-Difluorochrysene (6b)
1H NMR (500 MHz, CDCl3): δ 7.65–7.76 (m, 4H), 8.01 (d, J = 8.5 Hz, 2H), 8.22–8.27 (m, 1H), 8.67 (dd,
13
J = 9.2, 2.3 Hz, 1H), 8.73–8.78 (m, 1H), 9.20 (d, J = 7.8 Hz, 1H); C NMR (126 MHz, CDCl3): 120.0
(d, JCF = 9 Hz), 120.3 (d, JCF = 6 Hz), 120.4, 123.1, 123.6 (d, JCF = 15 Hz), 126.4 (dd, JCF = 3, 3 Hz),
126.7 (d, JCF = 2 Hz), 126.9, 127.14, 127.17, 127.3, 127.4, 128.0, 128.5, 128.6 (dd, JCF = 5, 5 Hz), 132.7,
144.3 (dd, JCF = 215, 14 Hz), 146.3 (dd, JCF = 218, 13 Hz); 19F NMR (470 MHz, CDCl3): δ 12.6 (d, J =
16 Hz, 1F), 21.6 (d, J = 16 Hz, 1F); IR (neat): ν~ 1647, 1381, 1242, 993, 812, 750, 640 cm–1; HRMS (70
eV, EI): m/z calcd. for C18H10F2 ([M]+): 264.0751; found:264.0744.
4.2.7.3. 5,6-Difluoropicene (6c)
1
60 mg, 63% yield (6c + 6c', 6c : 6c' = 89 : 11), colorless crystals; H NMR (500 MHz, CDCl3): δ 7.69
(dd, J = 7.8, 7.8 Hz, 1H), 7.72–7.78 (m, 3H), 8.01 (d, J = 8.5 Hz, 2H), 8.22–8.27 (m, 1H), 8.78–8.81 (m,
1H), 8.83 (d, J = 8.3 Hz, 1H), 8.88 (dd, J = 9.3, 2.0 Hz, 1H), 8.95 (d, J = 9.3 Hz, 1H), 9.16 (dd, J = 9.4,
2.9 Hz, 1H); 13C NMR (126 MHz, CDCl3): 120.5 (dd, JCF = 6, 6 Hz), 120.7 (d, JCF = 8 Hz), 121.2, 122.2,
123.20, 123.23, 123.23, 123.9 (d, JCF = 15 Hz), 124.8, 125.0, 126.8, 127.0 (d, JCF = 2 Hz), 127.1, 127.5,
127.8 (d, JCF = 3 Hz), 128.3, 129.8, 130.0, 131.9, 132.3, 144.7 (dd, JCF = 250, 15 Hz), 146.1 (dd, JCF
=
253, 13 Hz); 19F NMR (470 MHz, CDCl3): δ 13.0 (d, J = 15 Hz, 1F), 22.0 (d, J = 15 Hz, 1F); IR (neat):
ν~ 1645, 1250, 1011, 912, 741, 650 cm–1; HRMS (70 eV, EI): m/z calcd. for C22H12F2 ([M]+): 314.0907;
found: 314.0914; mp: 233–234 °C.
4.2.7.4. 13,14-Difluoropicene (6e)
1
92 mg, 98% yield, yellow crystals; H NMR (500 MHz, CDCl3): δ 7.69–7.77 (m, 4H), 8.00 (d, J = 9.3
Hz, 2H), 8.02 (d, J = 6.5 Hz, 2H) 8.72 (d, J = 9.3 Hz, 2H), 9.24 (d, J = 8.5 Hz, 2H); 13C NMR (126 MHz,
CDCl3): δ 121.1, 126.1 (dd, JCF = 4, 4 Hz), 127.37, 137.39, 127.62, 127.61 (dd, JCF = 30, 5 Hz), 128.1,