Convenient syntheses and photophysical properties of 1-thio- and 1-seleno-1,3-butadiene fluorophores in rigid dibenzobarrelene and benzobarrelene skeletons

Article abstract of DOI:10.1002/chem.201200761

No heavy-atom effect: Highly fluorescent, sulfur- or selenium-containing compounds were synthesized by intramolecular [4+2]-cycloadditions between 9-anthryl or 1-naphthyl and alkynyl moieties (see scheme). Their fluorescence is based on a 1-chalcogeno-1,3

Full text of DOI:10.1002/chem.201200761

COMMUNICATION
DOI: 10.1002/chem.201200761
Convenient Syntheses and Photophysical Properties of 1-Thio- and 1-Seleno-
1,3-Butadiene Fluorophores in Rigid Dibenzobarrelene and Benzobarrelene
Skeletons
Akihiko Ishii,* Tatsuro Annaka, and Norio Nakata[a]
Luminescent compounds have attracted considerable at-
tention in the fields of biochemistry[1] and materials science
as exemplified by organic light-emitting devices (OLEDs).[2]
In recent years, several types of fluorescent compounds with
heteroatoms, such as boron, silicon, phosphorus, and sulfur,
have been incorporated in conjugated systems,[3] in which
these heteroatoms provide crucial perturbations to the elec-
tronic nature of the HOMO and/or the LUMO of the corre-
sponding carbon counterparts. A significant characteristic of
these compounds is the dramatic change in photophysical
properties given by the chemical modification of heteroa-
toms. For example, oxides of fused thiophene derivatives ex-
hibit a bathochromic shift in emissions and, in some cases,
show larger quantum yields in the solid state than the corre-
sponding unoxidized derivatives.[4] Chalcogenides or com-
plexes with transition metals of phosphole derivatives exhib-
it similar properties.[5] In addition, some dendritic phosphole
oxides[6] show aggregation-induced emission (AIE).[7] These
outcomes provide useful chemistry for the heteroatom-con-
taining luminescent compounds.
The synthesis of 1 is based on the reaction of isolated or
intermediately formed chalcogenametallacycles 2 with di-
methyl acetylenedicarboxylate. In our studies, we have been
seeking to expand the substitution patterns of the 1-chalco-
geno-1,3-butadiene fluorophores to reveal the potential as
functional materials. Thus, we worked out an alternative
synthetic strategy, the intramolecular cycloaddition between
a 9-anthryl moiety and an alkynyl moiety, in which it is
straightforward to construct the dibenzobarrelene scaffold
accompanying an additional ring system in one process
[Eq. (1)].[9] Furthermore, this intramolecular cycloaddition
has the potential to synthesize the corresponding benzobar-
relene analogues by using 1-naphthyl as the ynophile,[10]
which would provide insight into the electronic and steric
roles of benzene rings fused on the barrelene core. In this
communication, we present the intramolecular [4+2]-cyclo-
additions of 1-(anthrylchalcogeno)- or 1-(naphthylchalcoge-
no)enynes I (E=S, Se) to synthesize dibenzobarrelene or
benzobarrelene derivatives II, respectively, which have a sub-
stitution pattern, which was hard to obtain by our previous
method, and are all highly fluorescent in solution. In addi-
tion, some of the oxide properties of the sulfur derivatives
are reported.
We recently reported fluorescent compounds 1 bearing
a 3-methylene-2,3-dihydrochalcogenophene in a rigid diben-
zobarrelene skeleton, in which 1-thio- and 1-seleno-1,3-buta-
dienes behave as the main contributor to the fluorescence.[8]
The fluorescence quantum yields (FF) of 1 in dichlorome-
thane were very high despite the presence of a heavy atom:
1.0 for 1 (E=S) and 0.86 for 1 (E=Se).
For the preparation of (9-anthrylthio)enyne 3 (Ar=Ph),
9-anthrylthiolate (AntSÀ), generated by the reduction of di-
9-anthryl disulfide with NaBH4 in EtOH and THF, was al-
lowed to react with 1,4-diphenyl-1,3-butadiyne (4a) at
reflux.[11] Unexpectedly, the reaction proceeded directly to
the desired final product 5a with 73% yield, indicating that
the enyne 3 (Ar=Ph) readily underwent an intramolecular
cycloaddition under the stated conditions (Scheme 1). In
a similar manner, dibenzobarrelenethio derivatives (here-
after, abbreviated as Dbb-S) 5 with aryl groups substituted
by an MeO (5b), F (5c), or CF3 (5d) group at the para posi-
tion and the corresponding selenium analogues (similarly
abbreviated as Dbb-Se) 6a–d were synthesized in high
[a] Prof. Dr. A. Ishii, T. Annaka, Dr. N. Nakata
Department of Chemistry, Faculty of Science and
Graduate School of Science and Engineering
Saitama University
255 Shimo-okubo, Sakura-ku, Saitama 338-8570 (Japan)
Fax : (+81)48-858-3394
E-mail: ishiiaki@chem.saitama-u.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200761.
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Scheme 1. Synthesis of dibenzobarrelene (Dbb) derivatives
5 and 6.
a) NaBH4, THF, EtOH, RT (for 4b (Ar=p-MeOC6H4): BuOH, DMF);
ꢀ À ꢀ
b) ArC C C CAr (4), THF, EtOH, reflux (for 4b: BuOH, DMF).
yields. In the case of MeO derivatives 5b and 6b, the reac-
tions were slow at reflux in EtOH/THF mixture due to the
p-donating methoxy substituent, which lowered the reactivi-
ty of diyne 4b toward nucleophile AntEÀ, so the syntheses
were performed at higher temperature at reflux in BuOH/
DMF (DMF=dimethyl formamide).
Figure 1. ORTEP drawing of Dbb-Se 6d (Ar=p-CF3C6H4) with 30%
probability ellipsoids. Selected bond lengths (ꢁ) and torsion angles (8):
À
À
À
À
C1 Se1: 1.960(2), Se1 C2: 1.915(2), C2 C3: 1.344(3), C3 C4: 1.432(3),
À
À
C1 C4: 1.546(3), C4 C5: 1.348(3); C3-C2-C19-C24: 29.2(3), C4-C5-C26-
C27: À55.5(3).
This synthetic strategy was successfully applied for the
synthesis of the benzobarrelene derivatives (monobenzobar-
relenes, abbreviated as Mbb-S and Mbb-Se) by employing
di-1-naphthyl dichalcogenides (Scheme 2). In this case, the
methane at room temperature gave the sulfoxide 11 (89%)
or the sulfone 12 (99%), respectively. Similarly, oxidation of
Mbb-S 9 with MCPBA (1 equiv) in dichloromethane at
room temperature gave the sulfoxide 13 with quantitative
yield and that with MCPBA (2 equiv) at reflux in dichloro-
methane yielded the sulfone 14 (66%). The structures of
11–14 were determined by spectroscopic methods and con-
firmed by X-ray crystallography for 11–13. Figure 2 presents
Scheme 2. Synthesis of benzobarrelene (Mbb) derivatives
9 and 10.
ꢀ À ꢀ
a) NaBH4, THF, EtOH, RT; b) PhC C C CPh (4a), THF, EtOH,
reflux; c) xylene, 1608C in an autoclave.
enyne intermediates 7 and 8 were isolated, and the cycliza-
tion was performed by heating their xylene solutions at
1608C in an autoclave to give Mbb-S 9 and Mbb-Se 10 with
72 and 54% yields, respectively.
The structures of 5–10 were determined by spectroscopic
methods and X-ray crystallography for 5 and 6.[12] A repre-
sentative ORTEP drawing of Dbb-Se 6d is depicted in
Figure 1. The bond lengths and angles of the 1-chalcogeno-
1,4-diaryl-1,3-butadiene part in Dbb-S 5 and Dbb-Se 6 are
in the normal ranges and almost independent of the sub-
stituents on the aryl groups. The five-membered rings with
a sulfur or selenium atom were planar. The torsion angles of
the aryl group attached at C2 to the planar five-membered
ring were smaller than those at C5 (5: Ar-C2: 4.3(4)–
17.4(4)8; Ar-C5: 25.9(3)–47.3(10)8; 6: Ar-C2: 6.5(4)–
33.9(3)8; Ar-C5: 38.5(3)–55.5(3)8).
Figure 2. ORTEP drawing of Mbb-SO 13 with 30% probability ellipsoids.
À
À
Selected bond lengths (ꢁ) and torsion angles (8): C1 S1: 1.8365(19), S1
À
À
À
À
C2: 1.8046(18), C2 C3: 1.358(2), C3 C4: 1.426(3), C1 C4: 1.537(2), C4
The oxidation of Dbb-S 6a with meta-chloroperoxybenzo-
ic acid (MCPBA, 1 equiv) or MCPBA (2 equiv) in dichloro-
À
C5: 1.350(3), S1 O1: 1.5033(14); C3-C2-C6-C7: À20.4(3), C4-C5-C12-
C13: À37.3(3).
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Syntheses and Photophysical Properties of Fluorophores
COMMUNICATION
an ORTEP drawing of Mbb-SO 13. In the oxidation of
Mbb-S 9, the formation of two diastereomeric sulfoxides
may be expected due to the presence of two chiral centers
at the bridgeheads [(RC*,RC*)]. In our study, we obtained
only one diastereomer (RS*,RC*,RC*)-13. In the recrystalli-
zation of 13, spontaneous crystallization occurred (the space
group of the single crystal is chiral P21).
have longer labs with larger e values and similar lem [1: labs =
359 nm (e=7400) and lem =488 nm; 2: labs =370 nm (e=
4700) and lem =494 nm, in dichloromethane], indicating that
the two aryl substituents in Dbb-E and Mbb-E have a sub-
stantial effect on labs and e values by the extension of conju-
gation. Stokes shifts of 1 and 2 are larger than Dbb-E and
Mbb-E (1: 7360 cmÀ1; 2: 6780 cmÀ1). Concerning the sub-
stituent effect in Dbb-S 5 and Dbb-Se 6, 5b, and 6b with
electron-donating p-MeO and 5d and 6d with electron-with-
drawing p-CF3 showed small bathochromic shifts in both labs
and lem compared with those of 5a and 6a (Ar=Ph). para-
Fluorine groups in 5c and 6c revealed slight hypsochromic
shifts.
In solution, compounds 5, 6, 9, and 10 showed blue (lem
479 nm for 6a) to green (lem 505 nm for 5d) fluorescence in
a relatively narrow region with almost quantitative quantum
yields (FF =0.97–1.0). It is clear that the free rotation of
aryl substituents has no influence on the quantum yield. Be-
cause these compounds involve cis,trans-1,4-diaryl-1,3-buta-
dienes in their fluorophores, their photophysical properties
were compared with those of 1,4-diphenyl-1,3-butadienes
(DPB). Although trans,trans-DPB is moderately fluorescent
(labs =332 nm, lem =373 nm, FF =0.42 in hexane), cis,trans-
DPB (labs =313 nm, FF <10À3 in hexane) and cis,cis-DPB
(labs =299 nm, FF <10À3 in hexane) are substantially non-
fluorescent by decay due to cis/trans isomerization and inter-
nal conversion.[13] In the DPBs, intersystem crossing is not
efficient and isomerization takes place through twisted inter-
mediates.[13] Thus, the present compounds demonstrate that
anchoring a flexible fluorophore in a rigid scaffold is quite
effective for emitting fluorescence, as has been seen in stil-
benes incorporated in rigid ladder-type structures.[3]
Photophysical properties of 5, 6, 9, and 10 are listed in
Table 1. Figure 3 shows UV/Vis and emission spectra of 5a,
6a, 9, and 10. Dbb-S 5 and Mbb-S 9 in dichloromethane
Figure 3. UV/Vis (c) and emission (g) spectra of 5a, 6a, 9, and 10.
In the solid state, Dbb-S 5 and Dbb-Se 6 have low (FF =
0.215 for 6a) to high (FF =0.812 for 5d) fluorescence quan-
tum yields. Compounds with an electron-donating MeO (5b
and 6b) and electron-withdrawing F and CF3 (5d, 6c, and
6d) substituents have relatively large quantum yields. In
a comparison between 5 and 6 with identical substituents,
the values are larger for Dbb-S 5 than those for Dbb-Se 6.
However, this is not the case for Mbb-S 9 (FF =0.090) and
Mbb-Se 10 (FF =0.200). In the crystals, no significant inter-
molecular interactions were observed except for 6d, in
showed the longest absorption maxima (labs) in the range of
378–398 nm with a molar extinction coefficient (e) of
17000–23000 and the emission maxima (lem) in the range of
491–505 nm. Dbb-Se 6 and Mbb-Se 10 in dichloromethane
exhibited labs in a similar region [381–399 nm (e=16000–
23000)] and blueshifted lem (479–490 nm). Thus, Dbb-S 5
and Mbb-S 9 have larger Stokes shifts (5300–6100 cmÀ1)
than Dbb-Se 6 and Mbb-Se 10 (4700–5200 cmÀ1). In compar-
ison with diesters 1 and 2, Dbb-E and Mbb-E (E=S, Se)
Table 1. Photophysical properties of 5, 6, 9, and 10.[a,b]
[c]
[c]
labs (e)
[nm
(mÀ1 cmÀ1)]
lem
FF
Stokes shift
[cmÀ1
labs (e)
[nm
(mÀ1 cmÀ1)]
lem
FF
Stokes shift
[cmÀ1
G
G
[nm]
R
]
G
E
[nm]
N
]
5a (H)
5b (OMe)
5c (F)
378 (23000)
388 (23000)
378 (17000)
398 (18000)
391 (19000)
491
0.996[d]
0.471[e]
1.0[d]
6100
5700
5900
5300
5500
6a (H)
384 (16000)
389 (23000)
381 (17000)
399 (17000)
391 (17000)
479
0.978[d]
0.215[e]
0.992[d]
0.604[e]
1.0[d]
5200
5200
5200
4700
5100
483[e]
497
472[e]
487
6b (OMe)
6c (F)
494[e]
486
0.690[e]
1.0[d]
481[e]
476
469[e]
505
0.687[e]
0.994[d]
0.812[e]
0.970[d]
0.090[e]
466[e]
490
0.252[e]
1.0[d]
5d (CF3)
9 (H)
6d (CF3)
10 (H)
514[e]
499
511[e]
488
0.465[e]
0.982[d]
0.200[e]
508[e]
486[e]
[a] The substituents at the para position of Ar groups are shown in parentheses. [b] In dichloromethane, unless otherwise noted. [c] Absolute fluores-
cence quantum yields were determined by using a calibrated integrating sphere system. [d] Under argon. [e] In the solid state.
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A. Ishii et al.
which an aromatic CH–p interaction (edge-to-face aromatic
interaction)[14] was observed between a hydrogen atom on
a benzene ring (C9-H, see Figure 1) and p-CF3C6H4 group
attached to the C2 carbon in a neighboring molecule
(CH···p: 2.511 ꢁ), which might contribute to the large bath-
ochromic shift (21 nm) from 490 nm in solution to 511 nm in
the solid state.
among three vinylene groups in barrelene than that among
three benzene rings in triptycene.[16] Another factor of the
decrease in HOMO levels of 15 and 16 compared with 17 is
presumably the electron-withdrawing effect of the benzene
ring(s).
Table 2 summarizes the photophysical data of oxides 11–
14. Compared with Dbb-S 5a and Mbb-S 9, large hypso-
chromic shifts were observed (17–37 nm for labs and 29–
Mbb-S 9 and Mbb-Se 10 exhibited both labs and lem at
somewhat longer wavelengths, by 13 and 7 nm and 8 and
9 nm, respectively, than the corresponding Dbb-S 5a and
Dbb-Se 6a. Time-dependent (TD)-DFT calculations[15] were
carried out on the unsubstituted model compounds 15 and
16 with barrelene derivative 17 as the reference to consider
the excitation energies and the shapes of HOMO and
LUMO. The calculated excitation energy of 16 (3.81 eV)
was smaller than that of 15 (3.88 eV), reproducing the bath-
ochromic shift of Mbb-S 9 (labs =391 nm) compared with
Dbb-S 5a (labs =378 nm). Figure 4 depicts the shapes of
HOMO and LUMO of 15–17, which indicate that their fluo-
rescence is based mainly on 1-thiobutadiene moieties with
some contribution from benzene rings and vinylene bridges.
In the HOMO of 15, orbital interactions exist between the
1-thiobutadiene conjugate system and benzene rings in
a mutual counterphase manner. This is the case for 16, in
which a vinylene p orbital takes part. As the number of ben-
zene rings decreases from 15 to 17, both the HOMO and
LUMO levels rise to a larger extent by the former, leading
to a decrease in the excitation energies. A plausible explana-
tion for the perturbation on energy levels of the 1-thiobuta-
diene conjugate systems in 15–17 is a larger through-space
interaction of (1-thiobutadiene)-vinylene than that of (1-thi-
obutadiene)-benzene, providing a larger contribution of the
vinylene bridge in HOMO than that of the benzene ring,
which is assumed from the larger through-space interaction
Table 2. Photophysical properties of oxides 11–14.[a]
[b]
labs (e) [nm (mÀ1 cmÀ1)] lem [nm] FF
Stokes shift [cmÀ1
]
11 361 (14000)
459
0.807[c] 5900
464[d]
462
0.388[d]
12 350 (17000)
13 365 (20000)
14 354 (19000)
0.792[c] 6900
0.672[d]
449[d]
453
0.019[c] 5300
0.597[d]
456[d]
453
0.020[c] 6200
0.144[d]
466[d]
[a] In dichloromethane, unless otherwise noted. [b] Absolute fluorescence
quantum yields determined by using a calibrated integrating sphere
system. [c] Under argon. [d] In the solid state.
46 nm for lem), which is in contrast with the case of the
oxides of fused thiophene derivatives exhibiting a bathochro-
mic shift.[4] These blueshifts are straightforwardly ascribed
À
À
to shortening of the conjugate system from C=C CH=C S
À
in 5a and 9 to C=C CH=C in 11–14 along with the electron-
ic effect of electron-withdrawing sulfoxide or sulfone
groups. The difference between Dbb-SO 11 and DbbSO2 12
is small in labs (11 nm) or negligible in lem (only 3 nm). This
is also true for Mbb-SO 13 and Mbb-SO2 14. However,
there are stark contrasts in their FF values. Although the FF
values of Dbb-SO 11 and DbbSO2 12 in solution remain
high (0.807 and 0.792, respectively) and are larger than
those in the solid state (0.388 and 0.672, respectively), those
of Mbb-SO 13 and Mbb-SO2 14 are quite low in solution
(both FF =0.020 in dichloromethane) but, in the solid state,
are enhanced to 0.597 and 0.144, respectively. This is attrib-
uted to the crystallization-induced emission (CIE) as ob-
served in polyACTHNUTRGNEUNG
(phenyl)-substituted conjugate systems.[7] AIE
was also observed for 13 and 14. In 100% THF, FF of 13
and 14 is 0.02, and in THF/H2O 5:95, the values rose up to
0.07 and 0.19, respectively, in which the emission wave-
lengths were redshifted (lem =474 nm for 13 and 483 nm for
14).
In summary, we have demonstrated the short-step and
high-yield syntheses of fluorescent compounds with 1,4-
diaryl-1-thio- or 1-seleno-1,3-butadienes as the fluorophores
in dibenzobarrelene (5 and 6) or benzobarrelene (9 and 10)
scaffolds by the intramolecular [4+2]-cycloaddition between
9-anthryl or 1-naphthyl and alkynyl moieties. These com-
pounds feature the fluorophores immobilized in a rigid skel-
eton and, at the same time, protected, in general, from inter-
molecular interaction by the nonplanar structures. Com-
pounds 5, 6, 9, and 10 are intrinsically fluorescent in solution
and hardly undergo the quenching by intersystem crossing,
Figure 4. Calculated labs, oscillator strength (f), HOMO (middle), and
LUMO (right) of model compounds 15–17 obtained by TD-DFT calcula-
tions at the B3LYP/6-31+GACTHNUTRGNE(NUG d,p) level.
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despite the presence of heavy atoms, nor non-irradiative re-
laxation resulting from intermolecular interactions. Al-
though their fluorescence quantum yields decrease in the
solid state, some still remain high (FF =0.812 for 5d and
0.690 for 5b and 5c). With respect to their oxides, some
characteristic properties were observed for benzobarrelene
derivatives 13 and 14. Their FF values in the solid state are
larger than those in solution (CIE), and AIE is observed.
Studies on their physical properties, such as electrochemis-
try, and the synthesis of derivatives with a wider range of
emission wavelengths are currently under investigation in
our laboratory.
[8] A. Ishii, Y. Yamaguchi, N. Nakata, Org. Lett. 2011, 13, 3702–3705.
[9] E. Ciganek, J. Org. Chem. 1980, 45, 1497–1505.
Experimental Section
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via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of Dbb-S 5a (Ar=Ph): A solution of di(9-anthryl) disulfide
(350 mg, 0.84 mmol) in THF (16 mL) was added slowly to a solution of
NaBH4 (170 mg, 4.49 mmol) in EtOH (15 mL) at 08C under argon. After
stirring for 30 min at 08C,
a solution of 1,4-diphenyl-1,3-butadiyne
(365 mg, 0.176 mmol) in EtOH (20 mL) was added to the mixture at 08C.
The mixture was heated at reflux for 12 h, and then the reaction was
quenched by addition of dilute hydrochloric acid. The mixture was ex-
tracted with dichloromethane, and the extract was washed with water,
dried over anhydrous Na2SO4, and evaporated to dryness. The residue
was subjected to column chromatography (hexane/CH2Cl2 4:1) to give 5a
(506 mg, 73%).
[13] a) W. A. Yee, S. J. Hug, D. S. Kliger, J. Am. Chem. Soc. 1988, 110,
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Keywords: cycloaddition
selenium · sulfur
· fluorescence · naphthalene ·
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Received: March 7, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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A. Ishii et al.
Intramolecular Cycloaddition
A. Ishii,* T. Annaka,
N. Nakata ...................... &&&& — &&&&
Convenient Syntheses and Photophys-
ical Properties of 1-Thio- and 1-
Seleno-1,3-Butadiene Fluorophores in
Rigid Dibenzobarrelene and Benzo-
barrelene Skeletons
No heavy-atom effect: Highly fluores-
cent, sulfur- or selenium-containing
compounds were synthesized by intra-
molecular [4+2]-cycloadditions
between 9-anthryl or 1-naphthyl and
alkynyl moieties (see scheme). Their
fluorescence is based on 1-chalcogeno-
1,3-butadiene-conjugated system in
a rigid skeleton. Some of them are also
highly fluorescent in the solid state.
The monoxide of Mbb-S is more fluo-
rescent in the solid state (FF =0.6)
than in solution (FF <0.02).
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www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!