Synthesis and optoelectronic properties of hexahydroxylated 10-O-R-substituted anthracenes via a new modification of the friedel-crafts reaction using o-protected ortho-acetal diarylmethanols

Article abstract of DOI:10.1002/chem.201101909

A new modification of the Friedel-Crafts type intramolecular cyclization involving O-protected ortho-acetal diarylmethanols as a new type of reactant, was carried out for the first time in a medium containing a large amount of water at room temperature an

Full text of DOI:10.1002/chem.201101909

DOI: 10.1002/chem.201101909
Synthesis and Optoelectronic Properties of Hexahydroxylated 10-O-R-
Substituted Anthracenes via a New Modification of the Friedel–Crafts
Reaction Using O-Protected ortho-Acetal Diarylmethanols
Agnieszka Bodzioch,[a] Bernard Marciniak,[b] Ewa Rꢀzycka-Sokołowska,[b]
˙
Jeremiasz K. Jeszka,[a, d] Paweł Uznan´ski,[a] Sylwester Kania,[c] Janusz Kulin´ski,[c] and
Piotr Bałczewski*[a, b]
4866
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876

FULL PAPER
Abstract: A new modification of the
Friedel–Crafts type intramolecular cy-
ACHTUNGTRENNUNGclization involving O-protected ortho-
acetal diarylmethanols as a new type of
reactant, was carried out for the first
time in a medium containing a large
amount of water at room temperature
and enabled synthesis of a series of
electron-rich, hexahydroxylated 10-O-
R-substituted anthracenes, where R is
tral 10-O-R-substituted benzene ring
was formed, fused to rings originating
from two independent aromatic alde-
hydes. The reaction proceeded via two
identified mechanisms involving acetal
and/or free aldehyde groups. The acid
sensitive acetal and dibenzyl alkoxy
functions have never been used togeth-
er in the intramolecular Friedel–Crafts
type cyclization. The new compounds
revealed deep blue fluorescence and
quantum yields in solution around 0.3.
The electrical properties investigated
for thin films obtained by vacuum dep-
osition on glass were 10-O-R-substitu-
ent dependent and showed much faster
transient current decay in the case of
the 10-O-CH2Ph derivative than for
the material with a 10-O-Me substitu-
ent (the lifetime of charge carriers was
25 times shorter in this case). The
AFM images of thin films, Stokes
shifts, and X-ray analysis of p-stacking
interactions in crystals of the new ma-
terials have been also obtained.
an alkyl (Me, nBu, n-C16H33) or ar
ACHTUNGERTNyNUNG l-
ACHTUNGTRENNUNGalkyl group (CH2Ph, CH2-2-Napht,
CH2C6H4CH2OAr) and also evaluation
of their electronic and optoelectronic
properties in solution, crystal, and solid
thin film. In this transformation, a cen-
Keywords: anthracenes
· cycliza-
tion · fluorescence · Friedel–Crafts ·
optoelectronic properties
Introduction
electroluminescent properties.[2] Many blue-light-emitting
materials with the anthracene core structure[3–11] have been
developed including one of the best known blue host materi-
al, 2-methyl-9,10-di(2,2’-naphthyl)anthracene (MADN).[12]
Although a theoretical maximum internal quantum efficien-
cy of nearly 100% has already been achieved in red and
green devices[13] yet the efficiency of deep blue phosphores-
cent OLEDs is not good enough for commercialization[14]
and therefore is a reason of further exploration.
In this paper, we report the synthesis, optical and electri-
cal properties of a series of 10-O-R protected (R=Me, nBu,
n-C16H33, CH2Ph, CH2-2-Napht, CH2C6H4CH2OAr) anthra-
cene systems 3a–f, as highly substituted and electron-rich
analogues of 9-methoxyanthracene 2 showing a deep blue
fluorescence (Scheme 1).
Organic electronics and optoelectronics are new fields of
basic knowledge and technology which have become a sub-
ject of interest to chemists, physicists and process engineers.
Therefore a search for organic semiconducting materials for
the construction of new generation, electronic devices such
as organic light emitting diodes (OLED), organic field-
effect transistors (OFET), organic solar cells (OPV), organic
solar concentrators (OSC), organic laser etc. has drawn the
attention of numerous multidisciplinary joint laboratories.
Among fused, polycyclic aromatic hydrocarbons, polyacenes
play an important role. Anthracene 1 and its derivatives are
particularly attractive due to high thermal stability, relative-
ly good solubility, low price, blue photoluminescent[1] and
The new anthracenes were obtained by the intramolecular
electrophilic substitution reaction operating on O-protected
ortho-acetal diarylmethanols. These compounds possessed
two chemical functions: acetal as the source of an active car-
bocation and dibenzylalkoxy, which have never been used
together in this type of the intramolecular Friedel–Crafts
type cyclization, carried out for the first time in a strongly
carbocation solvating medium containing a large amount of
water under very mild conditions.
´
[a] Dr. A. Bodzioch, Prof. J. K. Jeszka, Dr. P. Uznanski,
Prof. P. Bałczewski
Department of Heteroorganic Chemistry
Department of Polymer Physics
Department of Engineering of Polymer Materials
Center of Molecular and Macromolecular Studies
Polish Academy of Science
´
Sienkiewicza 112, 90-363 Łꢁdz (Poland)
Fax : (+48)426847126
E-mail: pbalczew@bilbo.cbmm.lodz.pl
In the literature, examples of the Friedel–Crafts type in-
tramolecular cyclization of o-formyl,[15] o-acyl[16] and o-car-
boxy[17] diarylmethanes and o-carboxy[18,19] diarylketones
leading to fused, polycyclic aromatic hydrocarbons are
known. In this type of reaction, except the first two and our
present modification, an additional step involving reduction
of intermediate products (anthrone or anthraquinone) is
necessary. Moreover, these reactions require harsh reaction
conditions (high concentrations of Brønsted acids and high
temperature).[20–22] Only a few examples of reactions carried
out under mild reaction conditions are known.[23,24] Our
modification employs a dilute aqueous methanolic solution
(2:1) of hydrochloric acid at room temperature, being the
[b] Dr. B. Marciniak, Dr. E. Rꢁz˙ycka-Sokołowska, Prof. P. Bałczewski
Department of Structural and Material Chemistry
Institute of Chemistry, Environmental Protection and Biotechnology
Jan Długosz University
Armii Krajowej 13/15, 42-200 Cze˛stochowa (Poland)
´
[c] Dr. S. Kania, J. Kulinski
Centre of Mathematics and Physics
´
Technical University of Łꢁdz
´
Al. Politechniki 11, 90-924 Łꢁdz (Poland)
[d] Prof. J. K. Jeszka
´
Department of Man-Made Fibres, Technical University of Łꢁdz
˙
´
ul. Zeromskiego 116, 90-543 Łꢁdz (Poland)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101909.
Chem. Eur. J. 2012, 18, 4866 – 4876
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4867

P. Bałczewski et al.
sensitive and, as mentioned,
have not been used together
before. Therefore, this modified
reaction is much more vulnera-
ble to changes of reaction con-
ditions than its original versions
and hence required tuning
which is also described below.
The new approach to substi-
tuted anthracenes arose from
the observation of a different
behavior of the O-benzyl pro-
tected diarylmethanol deriva-
tives 9a in the presence of 1n
HCl in benzene and methanol
Scheme 1. Blue-light emitting anthracenes 3a–f as examples of functionalized 1 and 2.
mildest reaction conditions ever used in this type of intra-
molecular cyclization.[25]
in synthesis of lignans.[25,29] We showed that this approach
could be extended to other polycyclic aromatic hydrocar-
bons containing nitrogen atoms like benzo[g]quinoline, ben-
zo[b]carbazole and pyrido[b]carbazole systems.[25,30] Thus, 9a
underwent a selective deacetalization in the presence of 1n
HCl in refluxing benzene to give the aldehyde 11a. Howev-
er, when the reaction was carried out in 1n HCl in aqueous
methanol (2:1), the unknown hexahydroxylated anthracene
Results and Discussion
Synthesis: The synthesis of a series of 10-O-R-substituted
anthracene derivatives 3a–e was based on transformation of
10-O-protected ortho-acetal di-
arylmethanols
(Scheme 2). The synthesis of
the branched anthracene
9
and
10
system 3 f is discussed separate-
ly (Scheme 3). The strategy of
the synthesis involved: i) pro-
tection of the aldehyde group
in 6-bromopiperonal 4 with 1,2-
ethanediol or 1,3-propanediol
to give acetals 5 or 6, respec-
tively. ii) The Br/Li exchange
reaction in 5 or 6 followed by
condensation with 3,4,5-tri-
ACHTUNGTRENNUNGmethACHTUNGTRENNUNGoxybenzaldehyde to afford
Scheme 2. Synthesis of the anthracene derivatives 3a–e. Reaction conditions: i) HO
ACHTUGNTRENUN(GN CH2)2OH/p-TsOH (cat.),
7 or 8. iii) protection of the hy-
droxyl group in 7 or 8 with an
alkyl or arylalkyl halide to
benzene, reflux, 26 h (for 5) or HO(CH2)3OH/p-TsOH (cat.), benzene, reflux, 4 h (for 6). ii) 1) nBuLi/n-hex-
AHCTUNGTRENNUNG
anes, THF, À788C, 15 min, 2) 3,4,5-trimethoxybenzaldehyde, THF, À788C to RT. iii) 1) NaH, THF, RT, 30 min,
2) RX (1.5 equiv), RT, 18 h (RX=MeI, PhCH2Br, NaphtCH2Br, nBuBr, n-C16H33I). iv) 1n HCl, MeOH, RT,
obtain protected diarylmetha- 60 h or 1n HCl, MeOH, reflux, 12 h (for 3e).
nols 9 or 10, iv) acid-driven cy-
ACHTUNGTRENNUNGclization of 9 or 10 to the corre-
sponding anthracene systems
3a–e (Scheme 2 and Scheme 3).
The last step is a Friedel–Crafts
type reaction and resembles its
later intramolecular modifica-
tion known as the Bradsher re-
action of ortho-acyl diaryl
ACHTUNGTRENNUNG
ACHTUNGTNERmNUNG eth-
anes.[26–28] Our modification of
this reaction differs from the
previous examples in that it em-
ploys reactants bearing two
functional groups, acetal and di-
Scheme 3. Synthesis of the anthracene derivative 3 f. Reaction conditions: i) 1) NaH, THF, RT, 30 min, 2) a,a’-
benzyl alkoxy, which are acid dibromo-p-xylene, THF, RT, 18 h. ii) 1n HCl, MeOH, RT, 6 days.
4868
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876

Synthesis and Optoelectronic Properties of Hexahydroxylated 10-O-R-Substituted Anthracenes
FULL PAPER
3a was formed unexpectedly in 68% yield (see Scheme 1 in
the Supporting Information).
formed more easily than their 5-membered analogues and
required six times shorter reaction times.
The anthracene 3a was also formed in case of the 1,3-di-
oxane protected diarylmethanol derivative 10a. The similar
53% yield (Scheme 2, Table 1) obtained in this case, sug-
gested that the type of acetal used for protection of the car-
bonyl function in O-protected ortho-acetal diarylmethanols
9 and 10 does not affect the efficiency of the cyclization pro-
cess. It is worth noting that the 6-membered acetals were
To optimize the conditions for the acid-catalyzed cycliza-
tion of 9a to the anthracene 3a, we tested a number of
acidic reagents, such as Lewis acid, Brønsted acid and strong
acidic ion-exchange resins. All the reactions afforded the an-
thracene 3a and the aldehyde 11a, accompanied in some
cases by the substrate 9a and the diarymethanol 7 with
a free hydroxyl group (see Table 1 in the Supporting Infor-
mation).
Optimized reaction condi-
Table 1. The final products: anthracenes 3 and aldehydes 11, obtained from 1,3-dioxolanes 9 and 1,3-dioxanes
10 under acidic conditions.
tions involving aqueous metha-
nol under very mild conditions
(1n HCl, MeOH, RT, 60 h)
were applied in this type of the
Friedel–Crafts cyclization for
the first time. They were next
used in the synthesis of the re-
maining 10-alkoxy (OMe, O-
nBu, O-n-C16H33) and 10-aryl-
methoxy (OCH2Ph, OCH2-2-
Substrates 9 or 10
Anthracene 3
Aldehyde 11
Napht,
OCH2C6H4CH2OAr)
substituted anthracenes 3b–f.
Unexpectedly, an attempt to
transform
O-n-hexadecyloxy
derivative 10e to the anthra-
cene 3e in the presence of 1n
HCl in methanol at room tem-
perature resulted in isolation of
the substrate 10e, accompanied
by trace amounts of the corre-
sponding aldehyde 11e. Finally,
refluxing 10e in methanol in
the presence of 1n HCl afford-
ed after 12 h the desired prod-
uct 3e in 38% yield (Scheme 2,
Table 1). The key derivatives 9,
10, and 12 were obtained by the
reaction of diarylmethanols 7
or 8 with alkyl or arylalkyl ha-
not isolated
AHCTUNGTERGlNNUN ides (methyl iodide, n-butyl
bromide, n-hexadecyl iodide,
2-(bromomethyl)naphthalene
and
a,a’-dibromo-p-xylene),
(Scheme 2
Table 1).
and
Scheme 3,
Following our successful syn-
thesis of the series of anthra-
cenes 3a–e in a single cycliza-
tion process, next we prepared
bis[(10-anthroxy)methyl]-1,4-ben-
AHCTUNGTERGzNNUN ene derivative 3 f, in which
two anthracene molecules are
connected via a p-xylene linker,
employing in one step two cy-
AHCTUNGTRENNUNG
Chem. Eur. J. 2012, 18, 4866 – 4876
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4869

P. Bałczewski et al.
of the diarylmethanol 7 with
a,a’-dibromo-p-xylene gave the
corresponding derivative 12 in
47% yield. Compound 12 in
the presence of 1n HCl was
next transformed into bis[(10-
anthroxy)methyl]-1,4-benzene
derivative 3 f (Scheme 3). Un-
expectedly,
compound
3 f
turned out to be very unstable
and underwent decomposition
during purification by column
chromatography. An attempt to
purify it by crystallization also
led to its degradation. Howev-
er, a small amount of the pure
product 3 f (15%) isolated by
preparative thin layer chroma-
tography (TLC) on silica gel,
allowed its unequivocal identifi-
1
cation using H NMR and MS-
EI. This system resembles
bis(9-anthroxy)methanes which
were reported to be photosensi-
tive below 400 nm due to the
high flexibility of the OCH2O
Scheme 4. Formation of anthracenes 3 via the aldehyde 11 and/or 1,3-dioxolane 9/1,3-dioxane 10 mechanistic
pathways.
spacer.[31] For experimental details, see the Supporting Infor-
mation.
Mechanistic studies and discussion: The mechanism of acid-
catalyzed cyclization of diarylmethanol derivatives to an-
thracene systems proposed previously[29] for the 1,3-dioxo-
lane derivatives can now be extended to 1,3-dioxane analogs
and may involve: 1) formation of the benzyl carbocation
13a as a result of protonation of acetal oxygen, followed by
opening of the five- or six membered acetal ring, 2) intramo-
lecular electrophilic Friedel–Crafts-type cyclization com-
bined with formation of the new six-membered ring 14a,
3) deprotonation and protonation sequence leading to 15a,
4) elimination of 1,2-ethanediol or 1,3-propanediol from 15,
5) final aromatization of 16a to the anthracene
(Scheme 4).
3
Scheme 5. Time dependent transformation of the O-protected diaryl-
ACHUTNGRENUmNG ethAHCUTNGTRENaNNGU nol 9a to the aldehyde 11a or the anthracene 3a using Amberlyst
15ꢂ. Reaction conditions: i) Amberlyst 15ꢂ, acetone, RT, 4 h. ii) Amber-
lyst 15ꢂ, acetone, RT, 24 h. iii) Amberlyst 15ꢂ, acetone, RT, 24 h. iv) 1n
HCl, MeOH, RT, 4 days.
Some results obtained during optimization of the cycliza-
tion conditions of 9a to 3a (See Table 1 in the Supporting
Information), especially those obtained for the reaction of
9a with the ion-exchange resin Amberlyst 15ꢂ in acetone,
suggested that the above mechanism could operate in paral-
aqueous methanolic solution of 1n HCl, the anthracene 3a
was isolated from 11a after four days in 47% yield
(Scheme 5, pathway iv).
lel with a mechanism of the direct cyclization of diaryl
ACHTUNGTNERmNUNG eth-
ACHTUNGTRENNUNGanols via free aldehydes to anthracenes, as in the Bradsher
reaction of o-formyl diarylmethanes.[26,27] Thus, the reaction
of the diarylmethanol 9a with Amberlyst 15ꢂ in acetone af-
forded after 4 h the aldehyde 11a in 96% yield, while after
24 h the anthracene 3a was isolated in 43% yield
(Scheme 5, pathway i and ii). The anthracene 3a was also
the main product of the reaction of the aldehyde 11a (ob-
tained in an independent way) with Amberlyst 15ꢂ in ace-
tone (Scheme 4, pathway iii). In a better cation solvating
In light of these results, the cyclization mechanism pro-
posed in Scheme 4 can be expanded by the additional possi-
bility of protonation of the aldehyde 11, and participation of
the protonated aldehyde 13b as the electrophilic species in
the first stage of cyclization. Other steps from 14b–16 would
proceed in an analogous way, and the final stage would in-
volve elimination of water instead of 1,2-ethanediol or 1,3-
propanediol (Scheme 5).
4870
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876

Synthesis and Optoelectronic Properties of Hexahydroxylated 10-O-R-Substituted Anthracenes
FULL PAPER
Thus, considerations of the mechanism of the above modi-
fication of the Friedel–Crafts type cyclization may be re-
duced to a question of participation in the cyclization of the
acetal pathway as an independent step. It seems that this
pathway operates, together with the aldehyde pathway, in
light of detection of the product 17 (m/z=388, MS-CI) con-
taining a glycol fragment, accompanied by 3a and 7, in the
reaction of 9a in the presence of FeCl3 as an acidic catalyst.
Similar intermediate compounds 18–20 (Scheme 6), contain-
ing 1,3-propanediol fragments were observed by Harvey and
co-workers,[32] in the cyclization of triaryl bis-o-acetals, car-
ried out in the presence of a strong acid. Moreover, carbo-
ACHTUNGTRENNUNGcatACHTUNGTRENNUNGions 13a and 13b which are stabilized in a similar way by
resonance, should have similar reactivity in the intramolecu-
lar, electrophilic substitution reaction.
Figure 1. Perspective views of a) 3b and b) 3d, showing the atomic num-
bering schemes. Displacement ellipsoids are drawn at the 30% probabili-
ty level and H atoms are shown as small spheres of arbitrary radii. The
À
red dashed line in b) denotes the intramolecular C H···O hydrogen
bond, which generates an S(6) graph-set motif.[34]
Scheme 6. Intermediate compounds observed in transformations of aryl
o-acetals under acidic conditions (17: this paper, 18–20: literature exam-
ples).
Crystal and molecular structures of anthracene 3b and an-
thracene 3d: The compounds 3b and 3d crystallized in the
¯
monoclinic P21/c (Z=4, Z’=1) and triclinic P1 (Z=2, Z’=
1) space groups, respectively. Similarly, as it was observed
for anthracene 3a (CSD[33] refcode ACOTUI[29]), in the case
of 3b and 3d molecules, anthracene and dioxolane rings as
a whole were essentially planar (Figure 1; see the Support-
ing Information for details).
Figure 2. Part of the crystal structure of 3b showing the (001) sheet built
up from R44(34) rings and formed by a combined effect of the two hydro-
gen-bonded C(9) and C(10) chains running along the crystallographic
The crystal structure of 3b contained two independent
À
weak non-conventional intermolecular C H···O hydrogen
À
b axis. The C H···O hydrogen bonds forming these chains are depicted
by red and blue dashed lines, respectively. All hydrogen atoms and the O
and C atoms of methoxy groups not involved in the hydrogen-bond
motifs have been omitted for clarity. Symmetry codes: (i) 1Àx, À1/2+y,
1/2Àz. (ii) 2Àx, 1/2+y, 1/2Àz.
bonds, which individually formed chains of C(9) and C(10)
types (Figure 2). The combined effect of these two hydrogen
bonds is the formation of a continuous two-dimensional
framework, that is, a sheet parallel to (001) and build up
from the R44(34) rings (Figure 2). In the crystal structure of
3d, there were three weak non-conventional intermolecular
tion forming a simple C(8) chain, additionally stabilized by
À
À
hydrogen bonds, that is, one hydrogen bond of the C H···O
one C H···p hydrogen bond (Figure 3). The molecules be-
longing to adjacent chains of this type were linked by the
À
type and two hydrogen bonds of the C H···p type. Each
À
molecule was connected to two others by the first interac-
second C H···p hydrogen bond and by the slipped p···p in-
Chem. Eur. J. 2012, 18, 4866 – 4876
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4871

P. Bałczewski et al.
Figure 3. Part of the crystal structure of 3d showing the two antiparallel
C(8) chains running along the crystallographic axis a and formed by the
À
À
C H···O and C H···p hydrogen bonds (red and navy blue dashed lines,
À
respectively). The black dashed and solid lines denote the C H···p and
p···p interactions, respectively, which connect the molecules of adjacent
chains. All H atoms, the O and C atoms of methoxy groups and the
carbon atoms of butoxy groups not involved in the above interactions
have been omitted for clarity. Symmetry codes: (i) 1+x, y, z. (ii) 1Àx,
1Ày, 1Àz. (iii) À1+x, y, z.
teraction (Figure 3). Moreover, it is worth noting that in the
crystal structures of 3b, 3d and also 3a there were stacks of
parallel in 3d and 3a or practically parallel in 3b anthracene
À
moieties (Figure 4a–c), without the C H···p interactions be-
tween their rings; these stacks run along the crystallographic
axes a or the [121]direction, respectively (see the Supporting
Information for details).
A comparisons drawn between the crystal structures of
3a, 3b, 3d, and those of their simple analogues, that is, un-
substituted anthracene 1 (CSD refcode ANTCEN[35]) and its
Figure 4. Packing structures of a) 3b, b) 3d, c) 3a, d) 1, and e) 2. Colum-
nar stacks of 3b, 3d, and 3a, respectively with a space-filling model for
planar moieties, and a ball-and-stick model for the substituents at the 10-
position; all hydrogen atoms and carbon and oxygen atoms of substitu-
ents at 1-, 2- and 3-positions have been omitted for clarity. d) and e) Her-
ringbone packing diagram of 1 and 2 with the space-filling model (the
methoxy substituent in 2 is drawn with the ball-and-stick model; all hy-
drogen atoms have been omitted for clarity).
¯ ¯
derivative
2 (i.e. 9-methoxyanthracene; CSD refcode
MXANTR01[36]), and also analysis of the ꢃpitchꢄ and ꢃrollꢄ
parameters [pitch (P) and roll (R) angles and pitch (dp) and
roll (dr) distances] estimated for these five compounds ac-
cording to the phenomenological approach proposed by
Curtis et al.[37] for the description of distortions from an
ꢃidealꢄ cofacial p stack and the values of the extent of the
area overlap of adjacent p-stacked molecules (AO), calcu-
lated according to a model proposed by Janzen et al.,[38] led
to the conclusions given below. A modification of molecular
structures of 1 or 2 by the replacement of three hydrogen
atoms at positions 1-, 2-, and 3- and two hydrogen atoms at
positions 6- and 7- by three methoxy groups and by a meth-
ylene-1,3-dioxy unit, respectively, results not only in an elim-
À
ination of intermolecular C H···p (arene) interactions be-
tween the benzene rings of the anthracene cores, but primar-
ily in a transformation of their arrangement, from typical
herringbone in 1 and 2 (Figure 4d and e; P<R, dp<dr) to
the parallel or practically parallel stacking in 3b, 3d, and 3a
(Figure 4a–c; P>R, dp>dr; Table 2). Moreover, a compari-
son of the AO values (Table 2) estimated for 3a, 3b, and
3d, that is, for the compounds belonging to the new group
of derivatives of 1,2,3-trimethoxy-6,7-(methylene-1,3-dioxy)
anthracene possessing a substituent at the 10-position, al-
lowed us to conclude that the extent of the area overlap be-
Table 2. p-Stacking distances (d; the shortest distance between the planes of anthracene moieties belonging to the two adjacent molecules (M) in the
stack), pitch (P, dp) and roll (R, dr) parameters and area overlaps (AO) for compounds 3b, 3d, and 3a.
Compound
Pair of molecules in the stacks
d
P
R
dp [ꢅ]
dr [ꢅ]
AO [%]
M3b(1), M3b (2)
2.768
3.863
3.369
3.465
3.834
3.494
62.71
59.13
61.7
62.4
60.94
49.45
15.58
24.98
50.53
10.10
34.75
47.24
5.34
6.46
6.26
6.63
6.90
4.08
0.77
1.80
4.09
0.62
2.66
3.78
9.4
1.5
–
2.9
0.1
–
¯
¯
3b
stack parallel to the [121] direction
M3b(1), M3b(3)
M3d(1), M3d(2)
M3b (1), M3d(3)
M3a(1), M3a(2)
M3a(1), M3a(3)
stack parallel to the axis a
3d
3a
between stacks
stack parallel to the axis a
[a] Excited at 355 nm. [b] Fluorescence quantum yields (fF) were determined by using anthracene (fF =0.29 in benzene) as the standard.[45]
4872
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876

Synthesis and Optoelectronic Properties of Hexahydroxylated 10-O-R-Substituted Anthracenes
FULL PAPER
Table 3. UV/Vis absorption and fluorescence properties of 3a, 3b, 3d,
and 3e in CH2Cl2 solution.
tween anthracene cores in the stacks of molecules depends
mainly on the nature of this substituent. Bearing in mind
that materials yielding p stacking with substantial spatial
overlap in the solid state are particularly attractive because
they often lead to devices with high charge carrier mobili-
ties[39–42] and taking into account the fact that in the crystal
structure of 3b such p stacking is predominant, it is possible
to suppose that of the group of derivatives, compound 3b
will turn out to be the most promising material for device
applications, particularly in the area of functional devices
such as organic field-effect transistors (OFETs). This suppo-
sition found a confirmation in the results obtained from in-
vestigations of optoelectronic properties of the synthesized
compounds (for more crystallographic details, see the Sup-
porting Information).
Compound
Absorption
lmax [nm]
Fluorescence
Stokes shifts
[cmÀ1
[b]
lmax [nm][a]
fF
N
]
3a
3b
3d
3e
331, 368, 391
354, 370, 389
359, 369, 389
270, 369, 390
399, 424
402, 424
401, 424
405, 425
0.26
0.32
0.29
0.27
513
813
769
950
[a] Excited at 355 nm. [b] Fluorescence quantum yields (fF) were deter-
mined by using anthracene (fF =0.29 in benzene) as the standard.[45]
crease of the alkyl chain length of the substituted group nor
its exchange to phenyl group lead to marked differences
with respect to peaks shape and spectral positions, which are
determined mostly by the anthracene core. Only a small
shift and a change of relative intensities of the maxima for
the longest wavelengths are observed.
The quantum yield of fluorescence (FF) calculated in
CH2Cl2 solution for methoxy 3b, butoxy 3d, benzoxy 3a,
and hexadecoxy 3e substituted anthracene derivatives oscil-
lated around the 0.3 value (Table 3) and were comparable
with the values determined for the unsubstituted anthracene
1 (FF =0.27[43]) and 1,4,5,8-tetraalkylsubstituted anthracenes
(FF =0.25–0.36, alkyl=Me, Et, nPr, nBu[44]). These results
indicate that both the type and position of substituents in
the anthracene ring do not affect the value of fluorescence
quantum yield in solution.
Photophysical properties in solution: UV/Vis absorption
spectra of benzoxy (3a), methoxy (3b), butoxy (3d), and
hexadecoxy (3e) substituted anthracene derivatives are
shown in Figure 5. The corresponding fluorescence spectra
Photophysical and electrical properties of thin films: Appli-
cation of organic compounds in molecular electronics re-
quires, in most cases, preparation of thin films. Such films of
compounds 3a, 3b, and 3d were prepared by vacuum evapo-
ration (10À5 Torr), on glass, spin casting or drop casting.
Films of the O-Me derivative 3b crystallized within 2–48 h
depending on the film thickness (thin films ca. 1 mm-slowly,
thick films ca. 2 mm-quickly). Progress of crystallization of
a 2 mm thick film is shown in Figure 7. One can see circular
Figure 5. Absorbances of anthracenes 3a (OCH2Ph), 3b (OMe), 3d
(OBu), and 3e (OC16H33) in CH2Cl2 solution. The inset shows magnifica-
tion of the long wavelength absorption (absorbance in a.u. for clarity).
are presented in Figure 6 and the positions of maxima, fluo-
rescence quantum yields (FF) and Stokes shifts are listed in
Table 3. It can be seen that (except for 3b) neither the in-
Figure 7. Progress in crystallization of a 2 mm-thick film of the O-Me de-
rivative 3b.
crystalline areas growing in time, which suggests spherulitic
growth with primary nucleation on impurities and subse-
quent secondary nucleation. However, the polarized optical
microscope pictures (Figure 8) revealed no preferential ori-
entation of the crystallites.
Figure 8b shows a typical AFM image of such a film and
the surface height profile (z direction). It can be seen that
higher regions of the surface which are probably related to
individual crystallites are about 0.7–1 mm long and protrude
Figure 6. Fluorescence of anthracenes 3a (OCH2Ph), 3b (OMe), 3d
(OBu), and 3e (OC16H33) in CH2Cl2 solution.
Chem. Eur. J. 2012, 18, 4866 – 4876
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4873

P. Bałczewski et al.
of the amorphous layer is of the order of 1.5 nm and it in-
creases to about 11 nm after crystallization.
Absorption spectra in the solid state were recorded for
thin layers (below 1 mm), obtained by vacuum evaporation
or spin coating (in the case of the O-Me derivative 3b, the
spectra were recorded before crystallization of the layer).
Low energy maxima, which can be observed are slightly
shifted to the blue as compared with the spectra of the same
compounds in solution. These data allow us to determine
the optical band gaps.
Figure 8. a) Polarized optical microscope picture of 1 mm thick evaporat-
ed layer of 3b. b) AFM image (4 mm), and c) its section analysis along
the line indicated on the image.
Figure 11 presents the results for the benzoxy 3a, meth-
AHCTUNGTREGoNNNU xy 3b, butoxy 3d and hexadecoxy 3e derivatives plotted in
by 30–80 nm from the surface. The surface roughness (Rrms
)
appropriate coordinates, assuming that these compounds are
direct semiconductors (Tauc plot). Extrapolation of the
linear part of the plots to absorption equal to zero gives the
value of the optical gap. The obtained band-gaps are:
3.08 eV for 3b and 3d, 3.21 eV for 3a, and 3.10 for 3e deriv-
atives. A similarity with the corresponding spectra in solu-
tion (Figure 5) suggests that in all cases molecular absorp-
tion dominates in the solid state and interactions between
the molecules are relatively weak. In the case of 3a, the dif-
ference is significant, which suggests that in this case the in-
teractions are relatively strong.
is 15 nm for the 1 mm film and increases with increasing film
thickness, reaching about 78 nm for a 4 mm film. Crystallite
size also increases up to about 2 mm.
Films of 3d obtained in the amorphous state also crystal-
lize after a few days forming crystals of various morpholo-
gies (Figure 9), which indicates that this compound can form
several polymorphic crystalline structures. Thus less suitable
for optoelectronic applications.
Figure 9. Polarized optical microscope pictures of a semicrystalline drop-
cast layer of 3d (after 5 days).
Films of 3a were obtained by both drop casting and
vacuum evaporation, in amorphous form (surface roughness
Rrms ca. 15 nm). Such layers are stable for at least a couple
of weeks but crystallize very slowly, forming after a few
months big spherulites with good crystallite orientation and
the classical maltese cross image observed under crossed po-
larizers (Figure 10).
Figure 11. Absorption of the 3a (O-CH2Ph), 3b (O-Me), 3d (O-Bu), and
3e (O-C16H33) derivatives plotted versus radiation energy to determine
the optical band-gap (3a and 3b: evaporated layers, 3d and 3e: spin-
coated layers).
AFM images of the sample surface in amorphous and
crystalline forms look similar at first sight but the roughness
Figure 12 shows fluorescence emission spectra of com-
pounds 3a, 3b, 3d and 3e in solution and in the solid state,
amorphous and crystalline layers. Crystalline layers were ob-
tained by crystallization of the initially amorphous layers.
The emissions of 3b, 3d, and 3e in the crystalline state are
similar to those in CH2Cl2 solution (only slightly (14 nm)
shifted to the red), which suggests that interactions between
these molecules in the solid state are weak.
The fluorescence spectrum thin layers of benzoxy deriva-
tive (3a; both in amorphous and crystalline state) is excep-
tionally broad. The band around 540 can be ascribed to for-
mation of excimer centers with relatively strong p-electron
interactions between the neighboring molecules. In the crys-
talline layers such centers are usually related to defects and
grain boundaries.[43] In solution, derivatives 3a, 3b, and 3d
Figure 10. a) Polarized optical microscope picture of the O-CH2Ph 3a
(1 mm thick evaporated layer). b) AFM image (height mode) and c) its
section analysis along the line shown in Figure 8b. The height differences
between the points indicated by triangles are 35 and 75 nm.
4874
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876

Synthesis and Optoelectronic Properties of Hexahydroxylated 10-O-R-Substituted Anthracenes
FULL PAPER
various voltages plotted in double logarithmic coordinates.
The inset shows the oscilloscope trace in linear coordinates.
A change of the slope in such plots can be due either to the
transit time of the light-induced charge carrier packet (dis-
persive transport[46] or multiple trapping) or to the life time
of charge carriers due to recombination of carriers of oppo-
site signs.[47,48]
As in our case, the time corresponding to the intersection
point is practically voltage independent, we can rule out the
first possibility. The determined lifetime of charge carriers
(holes) is about 200 ms. In the case of derivative 3a transient
currents decay is much faster. The lifetime is of the order of
magnitude of the flash lamp pulse so we can only estimate
that it is not longer than 7 ms.
Conclusion
Figure 12. Fluorescence emission spectra of 3a, 3b, 3d, and 3e deriva-
tives (as indicated in the Figures) in solution (S) and in the solid state:
amorphous layer (AmL) and crystalline layer (CrL; vacuum evaporated).
Excitation at 350 nm.
In summary, we performed a new approach to 10-O-R-sub-
stituted anthracenes via acid-catalyzed cyclization of O-pro-
tected ortho-acetal diarylmethanols as a new modification of
the Friedel–Crafts reaction. This modification involves acid
sensitive acetal and dibenzyl alkoxy groups contained in one
molecule and thence requiring special cyclization reaction
conditions. The advantage of our protocol over others ap-
plied in similar, intramolecular, electrophilic cyclizations, as
for instance in the Bradsher reaction (48% HBr in refluxing
acetic acid)[25,26] are much milder reaction conditions (1n
HCl, aqueous methanol or acetone at room temperature).
This transformation enabled synthesis of a series of blue-
light emitting, electron-rich hexahydroxylated anthracenes
according to two identified mechanisms. Their full crystallo-
graphic structures were determined and p-stacking interac-
tions were analyzed. Optoelectronic properties in solution
and solid thin films (absorption and emission spectra, Stokes
shifts, fluorescence quantum yields, optical band-gaps, and
the life time of charge carriers) were also determined. It was
found that the compound 3b with the best p stacking (as de-
termined by X-ray diffraction) had also the most promising
electrical properties due to long lifetime of charge carriers.
do not exhibit marked differences with respect to spectral
shape, or the wavelengths of absorption and fluorescence
peaks.
Figure 13 shows the time dependence of photoinduced
transient currents in the 10-methoxy derivative 3b layer for
Acknowledgements
The scientific work was financed from the Science Resources 2008–2013
as research grants (N20402232/0620, N204517139). We thank Prof. J. A.
Joule (The School of Chemistry, The University of Manchester) and
Stacy Joule for helpful discussion and correction of the manuscript.
[1] Y.-H. Kim, D.-C. Shin, S.-K. Kwon, Adv. Mater. 2001, 13, 1690–
1693.
[2] J. Shi, C. W. Tang, Appl. Phys. Lett. 2002, 80, 3201–3203.
[3] K. H. Lee, J. N. You, S. Kang, J. Y. Lee, H. J. Kwon, Y. K. Kim, S. S.
Yoon, Thin Solid Films 2010, 518, 6253–6258.
[4] Y. Li, M. K. Fung, Z. Xie, S.-T. Lee, L.-S. Hung, J. Shi, Adv. Mater.
2002, 14, 1317–1321.
Figure 13. Transient currents time dependence for 3b plotted in double
logarithmic coordinates. The intersection of the two slopes corresponds
to the lifetime of photogenerated charge carriers, which is approximately
3 ms. The insert shows a typical oscilloscope trace. The sample thickness
was 18.5 mm. A scheme of the investigated device and its picture are
shown in the bottom part of the figure.
[5] B. Balaganesan, W.-J. Shen, C. H. Chen, Tetrahedron Lett. 2003, 44,
5747–5750.
Chem. Eur. J. 2012, 18, 4866 – 4876
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4875

P. Bałczewski et al.
[6] Y. Kan, L. Wang, Y. Gao, L. Duan, G. Wu, Y. Qiu, Synth. Met. 2004,
141, 245–249.
[29] P. Bałczewski, M. Koprowski, A. Bodzioch, B. Marciniak, E. Rꢁ-
z˙ycka-Sokołowska, J. Org. Chem. 2006, 71, 2899–2902.
[7] Y.-H. Kim, H.-C. Jeong, S.-H. Kim, K. Yang, S.-K. Kwon, Adv.
Funct. Mater. 2005, 15, 1799–1805.
[30] P. Bałczewski, A. Bodzioch, E. Rꢁz˙ycka-Sokołowska, B. Marciniak,
´
P. Uznanski, Chem. Eur. J. 2010, 16, 2392–2400.
[8] M.-H. Ho, Y.-S. Wu, S.-W. Wen, T.-M. Chen, C.-H. Chen, Appl.
Phys. Lett. 2007, 91, 083515–083517.
[31] J. P. Desvergne, M. Gottag, J. C. Soulignac, J. Lauret, H. Bouas-Lau-
rent, Terrahedron Lett. 1995, 36, 1259–1262.
[9] Y.-Y. Lyu, J. Kwak, O. Kwon, S.-H. Lee, D. Kim, C. Lee, K. Char,
Adv. Mater. 2008, 20, 2720–2729.
[32] F.-J. Zhang, C. Cortez, R. G. Harvey, J. Org. Chem. 2000, 65, 3952–
3960.
[10] J. K. Park, K. H. Lee, S. Kang, J. Y. Lee, J. S. Park, J. H. Seo, Y. K.
Kim, S. S. Yoon, Org. Electron. 2010, 11, 905–915.
[11] S. E. Janga, C. W. Jooa, K. S. Yooka, J.-W. Kimb, C.-W. Leeb, J. Y.
Leea, Synth. Met. 2010, 160, 1184–1188.
[12] S. W. Wen, M. T. Lee, C. H. Chen, J. Disp. Technol. 2005, 1, 90–99.
[13] C. Adachi, M. A. Baldo, M. E. Thompson, S. R. Forrest, J. Appl.
Phys. 2001, 90, 5048–5051.
[33] F. H. Allen, Acta Crystallogr. Sect. A Acta Crystallogr. B 2002, 58,
380–388.
[34] J. Bernstein, R. E. Davis, L. Shimoni, N.-L. Chang, Angew. Chem.
1995, 107, 1689–1708; Angew. Chem. Int. Ed. Engl. 1995, 34, 1555–
1573.
[35] C. P. Brock, J. P. Dunitz, Acta Crystallogr. Sect. A Acta Crystallogr. B
1990, 46, 795–806.
[14] S. O. Jeon, K. S. Yook, C. W. Joo, J. Y. Lee, Adv. Funct. Mater. 2009,
19, 3644–3649.
[15] M. S. Newman, N. S. Hussain, J. Org. Chem. 1982, 47, 2837–2840.
[16] M. B. Andrus, Z. Ye, J. Zhang, Tetrahedron Lett. 2005, 46, 3839–
2842.
[36] V. Langer, H.-D. Becker, Z. Kristallogr. 1993, 206, 149–151.
[37] M. D. Curtis, J. Cao, J. W. Kampf, J. Am. Chem. Soc. 2004, 126,
4318–4328.
[38] D. E. Janzen, M. W. Burand, P. C. Ewbank, T. M. Pappenfus, H. Hi-
guchi, D. A. da Silva Filho, V. G. Young, J.-L. Bredas, K. R. Mann, J.
Am. Chem. Soc. 2004, 126, 15295–15308.
[17] R. G. Harvey, C. Cortez, T. Sugiyama, Y. Ito, T. W. Sawyer, J. Di-
A
[39] J. E. Anthony, D. L. Eaton, S. R. Parkin, Org. Lett. 2002, 4, 15–18.
[40] X.-C. Li, H. Sininghaus, F. Garnier, A. B. Holmes, S. C. Moratti, N.
Feeder, W. Clegg, S. J. Teat, R. H. Friend, J. Am. Chem. Soc. 1998,
120, 2206–2207.
[41] G. Horowitz, D. Fichou, D. Yassar, F. Garnier, Synth. Met. 1996, 81,
163–171.
[18] J. L. Hallman, R. A. Bartach, J. Org. Chem. 1991, 56, 6243–6245.
[19] K. L. Platt, F. Oesch, J. Org. Chem. 1981, 46, 2601–2603.
[20] R. Sangaiah, A. Gold, G. E. Toney, J. Org. Chem. 1983, 48, 1632–
1638.
[21] M. S. Newman, V. S. Prabhu, S. Veeraraghavad, J. Org. Chem. 1983,
48, 2926–2928.
[22] H. Ihmels, A. Meiswinkel, C. J. Mohrschladt, D. Otto, M. Waidelich,
M. Towler, R. White, M. Albrecht, A. Schnurpfeil, J. Org. Chem.
2005, 70, 3929–3938.
[23] C. K. Bradsher, E. F. Sinclair, J. Org. Chem. 1957, 22, 79–81.
[24] T. Yamato, N. Sakaue, N. Shinoda, K. Matsuo, J. Chem. Soc. Perkin
Trans. 1 1997, 1193–1199.
[42] J. G. Laquindanum, H. E. Katz, A. J Lovinger, A. Dodabalapur,
Adv. Mater. 1997, 9, 36–39.
[43] H. Nakayama, Chem. Phys. Lett. 1998, 289, 275–280.
[44] C. Kitamura, Y. Abe, N. Kawatsuki, A. Yoneda, K. Asada, T. Ko-
bayashi, H. Naito, Mol. Cryst. Liq. Cryst. 2007, 474, 119–135.
[45] W. R. Dawson, M. W. Windsor, J. Phys. Chem. 1968, 72, 3251–3260.
[46] H. Scherr, E. W. Montroll, Phys. Rev. B 1975, 12, 2455–2477.
[47] H. Fritzsche, Proc. Int. Summer School on Semiconductors, ESPOO,
Helsinki, 1982, p. 2.
[25] This reaction was a subject of patent applications: P. Bałczewski, A.
Bodzioch, J. Skalik, P-396700, 2011; P. Bałczewski, A. Bodzioch, J.
Skalik, P-389778, 2009; P. Bałczewski, A. Bodzioch, M. Koprowski,
J. Skalik, P-385794, 2008. (all from the Center of Molecular & Mac-
[48] S. Kania, M. Dłuz˙niewski, Diamond Relat. Mater. 2005, 14, 74–77.
´
romolecular Studies PAS, Łꢁdz, Poland).
[26] C. K. Bradsher, J. Am. Chem. Soc. 1940, 62, 486–488.
[27] C. K. Bradsher, F. A. Vikgiello, J. Org. Chem. 1948, 13, 786–789.
[28] C. K. Bradsher, Chem. Rev. 1987, 87, 1277–1297.
Received: June 21, 2011
Revised: February 10, 2012
Published online: March 21, 2012
4876
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 4866 – 4876