Mechanochemical Synthesis, Photophysical Properties, and X-ray Structures of N-Heteroacenes

Article abstract of DOI:10.1002/ejoc.201600005

The described mechanochemical methodology is an example of a proof-of-concept in which solution-based tedious, poor yielding, and difficult syntheses of pyrazaacenes are achieved under solvent-free ball-milling conditions; the method is easy, high yieldin

Full text of DOI:10.1002/ejoc.201600005

DOI: 10.1002/ejoc.201600005
Full Paper
Heteroacene Synthesis
Mechanochemical Synthesis, Photophysical Properties, and
X-ray Structures of N-Heteroacenes
Prasit Kumar Sahoo,[a] Chandan Giri,[a,b] Tuhin Subhra Haldar,[a] Rakesh Puttreddy,[b]
Kari Rissanen*[b] and Prasenjit Mal*[a]
Abstract: The described mechanochemical methodology is an common solvents, and column chromatographic purifications
example of a proof-of-concept in which solution-based tedious, could be avoided after the solvent-free syntheses. The UV/Vis
poor yielding, and difficult syntheses of pyrazaacenes are absorption spectra of the pyrazaacenes show intense absorp-
achieved under solvent-free ball-milling conditions; the method tion bands in the near-IR region. The single-crystal X-ray analy-
is easy, high yielding, time-efficient, and environmentally be- ses of selected pyrazaacene derivatives showed pairwise π–π
nign. The synthesized compounds also include pyrazaacenes interactions and some C–H···π interactions, which could ac-
(N-heteroacenes) that are octacene analogues containing pyr- count for some of the photophysical features of the compounds
ene building blocks. The compounds were sparingly soluble in in the solid state.
Introduction
Herein, we mainly focus our attention on the synthesis of
pyrazaacenes or N-heteroacenes, that is, nitrogen-containing
heteroacenes with either pyrene building blocks or pyrene-
fused oligoazaacenes. In general, N-heteroacenes are synthe-
sized by two popular methods: (1) cyclocondensation reactions
between 1,2-diaminoarenes and 1,2-diketones;[5] (2) substitu-
tion reactions of 1,2-diaminoarenes with dihydroxyacenes, fol-
lowed by oxidation.[3,4] However, these pyrazaacenes are syn-
thesized by following the cyclocondensation method, be-
cause –C=N bonds are readily constructed through this reac-
tion.[5b] The major disadvantages of the known syntheses of
pyrazaacenes are associated with the hazardous reaction condi-
tions and low yields; therefore, very few methods are available
for pyrazaacene synthesis.[5a,6]
The recent advances in the syntheses of extended π-conjugated
acene molecules with exciting optoelectronic properties have
led to significant interest in these compounds for materials sci-
ence.[1] Generally, acenes are considered as the most compre-
hensive class of fused polycyclic aromatic hydrocarbons and
are described by the fewest localized Clar resonant sextets per
number of aromatic rings.[2] The uses of these materials vary
from moth repellents to precursors for synthetic dyes such as
alizarin. Also, owing to their electronic properties, these mol-
ecules have gained attention for applications such as field-
effect transistors (FETs), organic light-emitting diodes (OLEDs),
and photovoltaic cells. Unfortunately, acenes are highly unsta-
ble, and the incorporation of heteroatoms increases their stabil-
ity.[3] These heteroacenes display improved stability compared
to their hydrocarbon analogues because it is much easier to
make C–N bonds than C–C bonds.[4] Owing to their electron-
deficient nature, small band gaps, and high thermal stabilities,
heteroacenes are considered to be alternatives to acenes as po-
tential n-type semiconducting materials.[1d,3]
Recently, as result of public interest in alternative energy in-
put,[7] ball-milling mechanochemistry[8] has received significant
interest from chemists as a solvent-free synthetic methodology
owing to its benefits over traditional solution-based methods.[9]
The advantages of mechanochemistry are substantial and well-
documented.[7] This technique has huge significance to green
processes and is time efficient, environmentally benign, and
economical. The minimum purification required, quantitative
conversions, and the production of fewer byproducts bring ex-
tra importance to this method. Under the area of mechano-
chemistry, we have recently reported multistep syntheses,[10]
metal-free synthetic methodologies,[11] and self-sorting reac-
tions.[12] Therefore, we have anticipated that solvent-free syn-
thesis by the ball-milling methodology may possibly be used
as a supply of mechanical energy and that reactions for the
synthesis of heteroacenes could be performed in a greener
way.[13] Taking into consideration all of these aspects, we have
designed a straightforward mechanochemical route for the
[a] School of Chemical Sciences, National Institute of Science Education and
Research (NISER) Bhubaneswar,
PO Bhimpur-Padanpur, Via Jatni, District Khurda, Odisha 752050, India
E-mail: pmal@niser.ac.in
http://www.niser.ac.in/users/pmal
[b] University of Jyvaskyla, Department of Chemistry, Nanoscience Center,
P. O. Box. 35, 40014 University of Jyvaskyla, Finland
E-mail: kari.t.rissanen@jyu.fi
https://www.jyu.fi/kemia/tutkimus/orgaaninen/en/research/rissanen
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejoc.201600005.
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preparation of N-heteroacenes in a limited number of synthetic
steps, under solvent-free conditions, and in high yields.
Results and Discussion
Synthesis
The mechanochemical (ball-milling) syntheses of heteroacenes
from their respective precursors are outlined in Figure 1. 1,2-
Dicarbonyl compounds (1) and 1,2-diaminoarenes (2) were
used as precursors for the solvent-free cyclocondensation reac-
tions. The reactions were performed under ambient laboratory
conditions with p-toluenesulfonic acid (PTSA) as the catalyst.
For optimization, the reaction progress was monitored by thin
layer chromatography (TLC) or 1H NMR spectroscopy. As a
standard method, the milling instrument was stopped, and a
small sample was collected from the reaction jar and analyzed.
After the reactions were complete, the solid products were col-
lected in a flask, washed with an appropriate solvent, and col-
lected by filtration. The substrate scope of this methodology
was verified, and the results are shown in Figure 2.
As shown in Figure 2 (a), excellent yields (91–95 %) of pyr-
azaacene derivatives were obtained from pyrene-4,5-dione
(1a)[14] and different diamines. Similar high-yielding reactions
were observed for the synthesis of pyrazaacene derivatives from
other dicarbonyl or tetracarbonyl derivatives (Figure 2, b–d). In
the majority of cases, a single product was obtained; therefore,
purification by washing with an appropriate solvent (mainly
highly polar solvents) led to the isolation of analytically pure
1
products (Figure 3, H NMR spectra). By this methodology, we
also synthesized the octacene derivatives benzo[i]benzo[6′,7′]-
quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine (3bb)[15]
and 2,13-di-tert-butylbenzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]-
Figure 1. Mechanochemical approach for heteroacene synthesis.
Table 1. Efficiency of the synthesis by ball milling.
Entry
1
Information
Previous work
ref.[16]
pyridine, reflux, Ar atm, 3 d
workup and then flash chromatography
This work
ball mill
r.t., 3 h, PTSA catalyst
solid residue washed with ethanol
95
ball mill
r.t., 4 h, PTSA catalyst
solid residue washed with ethanol and then
DMF
78
3ab
3bb
method:
reaction conditions:
isolation procedure:
yield [%]
method:
reaction conditions:
isolation procedure:
32
2
3
ref.[17]
pyridine, 120 °C, Ar atm, 3 d
solid residue washed with ethanol and then
chloroform
yield [%]
method:
40
3db
ref.[5a]
ball mill
reaction conditions:
isolation procedure:
pyridine, 120 °C, Ar atm, 3 d
solid residue washed with ethanol and chloro- solid residue washed with ethanol and then
r.t., 4 h, PTSA catalyst
form
32
DMF
76
yield [%]
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Figure 2. The mechanochemically synthesized N-heteroacenes are shown with their compound identification numbers, reaction times, and isolated yields.
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Figure 3. 1H NMR spectra of 3aa, 3cb, 3ee, and 3gg in CDCl3. No purifications of these compounds were performed before the spectra were recorded.
phenanthro[4,5-abc]phenazine (3db) in good yields. The studies. As representative examples, the 1H NMR spectra of 3aa,
octacenes (3bb and 3db) were purified by washing with highly 3cb, 3ee, and 3gg without any purification are shown in Fig-
polar solvents such as N,N-dimethylformamide (DMF).
ure 3. Thus, the efficiency of this ball-mill method for the syn-
thesis of N-heteroacenes has been established.
As pyrazine is one of the most important heterocyclic cores
in heteroacene systems, we extended our methodology to
other classes of N-heteroacene analogues. By using different
1,2-diketones (Figure 1, b) such as benzil (1g), 1,10-phen-
anthroline-5,6-dione (1e), and phenanthrene-5,6-dione (1f), we
synthesized different classes of N-heteroacenes in excellent
yields (Figure 2, e–g). Similarly, the bis(phenazine) 3eg and the
bis(quinoxaline) 3gg were also obtained in excellent yields
(ca. 90 %) from (1,1′-biphenyl)-3,3′,4,4′-tetraamine (2g) and
benzene-1,2,4,5-tetraamine (2h), respectively.
The commonly used methods to synthesize pyrazine-con-
taining heteroacenes use ethanol/acetic acid or acetic acid un-
der reflux in the presence of the oxidant 2-iodoxybenzoic acid
(IBX). In all of these cases, the reaction conditions are hazard-
ous, time consuming, and often lead to very poor yields. Inter-
estingly, this method is simple, convenient, time-efficient, eco-
nomical, and environmentally friendly. A comparison of the syn-
theses of a few heteroacenes by our method and by literature
methods is presented in Table 1. Hence, it is established that
our methodology for the synthesis of heteroacenes is superior
to the existing ones.
Photophysical Study[18]
The absorption and photoluminescence spectra of the com-
pounds were recorded in appropriate solvents, and selective
data are shown in Table 2. The absorption maxima of the com-
pounds above λ = 400 nm are due to n–π* transitions. As ex-
pected, with increasing conjugation, more redshifted absorp-
tions were observed, for example, λmax ≈ 435 nm for 3aa and
469 nm for 3ab. The UV/Vis absorption spectra of pyrazaacenes
3aa–3ae in dichloromethane are shown in Figure 4.
Table 2. Absorption maxima, emission maxima, and fluorescence quantum
yields for selected compounds.
λabs [nm]
λem [nm]
Φ
3aa
3ab
3ac
3ad
3ae
3ca
3cb
3cc
3cd
3cf
435
469
434
447
452
439
474
438
455
456
412
417
415
419
471
502
462
490
494
480
511
471
507
503
442
446
443
440
0.35
0.16
0.47
0.12
0.02
0.42
0.17
0.48
0.32
0.08
0.10
0.23
0.11
0.28
1H NMR Spectroscopy
The solvent-free syntheses were performed under ambient con-
1
ditions, and H NMR spectroscopy studies helped us to under-
stand the efficiency of this described methodology. No chro-
matographic purifications were performed; however, by wash-
ing the products with minimum quantities of highly polar sol-
vents, the compounds were isolated with high purity for further
3ba
3bc
3da
3dc
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Figure 4. UV/Vis absorption spectra of pyrazaacenes 3aa–3ae in dichloro-
methane (1 × 10–5
).
M
Crystallographic Investigations
The molecular structures of polycyclic aromatic hydrocarbons
(PAHs) are not very interesting.[1e] However, heteroatom-con-
taining PAHs and their solid-state organizational features such
as enhanced π–π interactions are very interesting and can be
understand through X-ray crystallography.[19] In the solid-state,
the extent of π–π and C–H···π interactions in N-heteroacenes
are believed to be further improved by the substituents and
any π disturbances caused by the inclusion of charged species.
These concepts are explored within the crystal structures of
3ac, 3ae, 3ba, and 3cf, as are the forces that drive the associa-
tion of the aromatic rings through π–π and C–H···π interac-
tions.[18,20]
All of the crystal structures show characteristic π–π interac-
tions, as shown in Figure 5. Compound 3ac displays a herring-
bone pattern (Figure S45) with the aromatic rings displaced lat-
erally and stabilized by pairwise π–π interactions at centroid-to-
centroid distances of 3.562 to 3.786 Å. Additionally, the lateral
displacement allows the methyl substituents to form C–H···π
interactions (ca. 2.780 to 3.022 Å), as shown in Figure 5 (b). In
3ae, the aromatic rings are displaced such that the bromine-
substituted benzene ring stacks uniquely above the pyrazine
ring stabilized by pairwise π–π interactions (ca. 3.532 to
3.849 Å), as shown in Figure 5 (d). The packing of 3ae is influ-
enced by the bromine substituents and again displays a her-
ringbone solid-state organization stabilized by π–π and Br···Br
interactions (ca. 3.602 Å). All of the interatomic distances in the
crystal-packing interactions are shorter than the sum of the van
der Waals radii (Figure S46).
Figure 5. Left: X-ray crystal structures of (a) 3ac, (c) 3ae, (e) 3ba, and (g) 3cf
with thermal ellipsoids at 50 % probability level. Hydrogen atoms are not
labeled for clarity. Right: the corresponding motifs showing π–π interactions.
of the trifluoroacetate anions are further stabilized by unsym-
metrical O···H···O hydrogen bonds with distances of 1.21(5) and
1.23(4) Å [angle O···H···O 167(4)°], as shown in Figure 5 (f). The
crystal packing is further extended one-dimensionally by π–π
interactions (ca. 3.737 Å) and two dimensionally by weak C–
H···O interactions between the trifluoroacetate anions and the
hydrogen atoms of the aromatic rings to generate herringbone
(viewed along the a axis) and sinusoidal (viewed along the c
axis) patterns (Figure S46). Although the C–H···O interactions
deviate by 0.122 Å from the sum of the van der Waals radii and
are caused by the packing, they are important in the crystal-
packing stabilization. The efficient π-cloud delocalization be-
tween the pyrene core with electron-donating tert-butyl-substi-
tuted and pyrazine-fused benzene rings with electron-with-
drawing chloride substituents results in strong π–π interactions
in 3cf. The π–π interactions occur one-dimensionally without
aromatic-ring displacements (Figure S47) but in an inverted
fashion to avoid steric hindrance between the tert-butyl groups,
as shown in Figure 5 (h). The centroid-to-centroid distances
range from 3.415 to 3.698 Å. The crystal packing of 3cf is trivial,
and all of the observed C–H···π interactions are above the sum
of the van der Waals radii. The Hirshfeld surface plots and 2D
fingerprint analyses are given in the Supporting Information.
As shown in Figure 5 (f), 3ba clearly has the most-abundant
and efficient π–π interactions (ca. 3.608 to 3.808 Å) of all of the
compounds. This can be accounted for by the protonation of a
pyrazine nitrogen atom. The N–H moiety acts as a bifurcated
hydrogen-bond donor for two trifluoroacetate C–O oxygen at-
oms with slight double-bond character [1.211(3) Å] at distances
Conclusions
of 2.726(3) [angle N–H···O 144°] and 2.802(3) Å [angle N–H···O We foresee that the benefits of the mechanochemical synthesis
115°]. On the other hand, the C–O oxygen atoms [1.273(3) Å] of the pyrazaacenes will be substantial: (a) this could potentially
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11,12-Dimethylphenanthro[4,5-abc]phenazine (3ac): Pale or-
ange solid; yield 94 % (67 mg); m.p. 238–240 °C. 1H NMR (400 MHz,
CDCl3): δ = 9.54 (d, J = 7.7 Hz, 2 H), 8.26 (d, J = 7.7 Hz, 2 H), 8.08–
8.05 (m, 4 H), 8.02 (s, 2 H), 2.58 (s, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 142.6, 141.7, 140.9, 131.6, 130.0, 128.9, 128.5, 127.3,
be the most efficient approach for heteroacene synthesis; (b)
the room-temperature synthesis, shorter reaction time, and sim-
plified purification procedure will make the heteroacenes
cheaply available for materials chemistry applications. The X-ray
crystal analysis of a few pyrazaacene derivatives show pairwise
π–π interactions and some C–H···π interactions, which may re-
sult in conductivity properties in the solid state. We are explor-
ing the conducting behavior of the N-heteroacenes. Further, we
anticipate that our study may receive substantial attention from
researchers working on the development of synthetic method-
ologies with N-heteroacenes as well as chemists searching for
superior methods in organic mechanochemistry.
126.9, 126.1, 123.7, 20.7 ppm. IR (KBr): ν = 3041, 2920, 2848, 1613,
˜
1354, 1295, 1096, 1001, 867, 831, 719, 438 cm–1. HRMS: calcd. for
C24H16N2 [M + H]+ 333.1386; found 333.1410.
Phenanthro[4,5-abc]phenazine-11-carboxylic Acid (3ad): Or-
ange solid; yield 91 % (68 mg); m.p. 246–248 °C. 1H NMR (400 MHz,
CDCl3): δ = 9.57 (s, 2 H), 9.41 (s, 1 H), 8.80 (s, 2 H), 8.60 (dd, J = 22.0,
6.9 Hz, 2 H), 8.25 (s, 2 H), 8.19 (q, J = 9.3 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 170.0, 144.68, 140.7, 138.4, 136.0, 135.8, 134.5,
134.4, 133.2, 132.6, 132.4, 131.0, 128.9, 128.8, 128.7, 128.2, 127.5,
127.4, 126.5, 126.4, 124.8, 124.3, 121.8 ppm. IR (KBr): ν = 3050, 2880,
˜
1688, 1680, 1435, 1358, 1283, 1206, 1134, 1023, 832, 801,
714 cm–1. HRMS: calcd. for C23H12N2O2 [M + H]+ 349.0972; found
349.0993.
Experimental Section
General Methods: Ball-mill syntheses (21 Hz) were performed in
the open atmosphere with a Retsch MM 200 mixer mill in a 10 mL
ZrO2 or stainless-steel jar with one ball of 15 mm diameter made
of ZrO2 or stainless-steel, respectively. The NMR spectra were re-
corded with a 400 MHz instrument at 25 °C. The chemical shift
values are reported in parts per million (ppm) and were referenced
11,12-Dibromophenanthro[4,5-abc]phenazine (3ae): Yellow
1
solid; yield 95 % (85 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3):
δ = 9.43 (s, 2 H), 8.87 (s, 2 H), 8.50 (d, J = 6.5 Hz, 2 H), 8.18 (s, 2 H),
8.10 (s, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 141.8, 136.0, 134.0,
132.2, 132.1, 129.9, 128.5, 128.2, 126.5 126.4, 123.8 ppm. IR (KBr):
1
ν = 3063, 3046, 2917, 2843, 1624, 1442, 1353, 1293, 1171, 1099,
to the residual chloroform (δ = 7.26 ppm for H, δ = 77.16 ppm for
˜
1080, 903, 833, 714, 434 cm–1. HRMS: calcd. for C22H10Br2N2 [M +
H]+ 460.9283; found 460.9253.
13C) and deuterium oxide signals (δ = 4.79 ppm for H). The peak
1
patterns are designated as follows: s singlet, d doublet, t triplet, q
quartet, m multiplet, dd doublet of doublets, td triplet of doublets,
br. s broad singlet. The coupling constants (J) are reported in Hertz
(Hz). High-resolution mass spectrometry (HRMS) was conducted
with an ESI-TOF mass spectrometer. The infrared spectroscopic data
are reported in wavenumbers (cm–1). The melting points of the
compounds were determined with a digital melting point appara-
tus.
Quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine
(3ba):
Pale yellow solid; yield 92 % (71 mg); m.p. >300 °C (ref.[22] >420 °C).
1H NMR (400 MHz, CDCl3): δ = 9.98 (d, J = 8.0 Hz, 4 H), 8.79 (dd, J =
6.4, 3.3 Hz, 4 H), 8.59 (t, J = 8.0 Hz, 2 H), 8.40 (dd, J = 6.5, 3.1 Hz, 4
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 130.0, 137.7, 136.4, 132.1,
131.0, 128.9, 126.1, 125.2 ppm. IR (KBr): ν = 3053, 3011, 2923, 1957,
˜
1903, 1613, 1479, 1415, 1403, 1356, 1332, 1294, 1231, 1133, 1101,
976, 870, 809, 759, 720, 615, 570, 515, 443 cm–1. HRMS: calcd. for
C28H14N4 [M + H]+ 407.1291; found 407.1290.
Phenanthro[4,5-abc]phenazine (3aa): Pyrene-4,5-dione (1a,
50 mg, 0.21 mmol), o-phenylenediamine (2a, 23 mg, 0. 21 mmol),
PTSA (4 mg, 0.021 mmol), and a stainless-steel ball were added to
a stainless-steel jar (10 mL). Milling was performed for 3 h, after
which the crude reaction mixture was washed with ethanol to iso-
late the product as yellowish solid; yield 94 % (62 mg); m.p. 257–
Benzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]-
phenazine (3bb):[17] Orange solid; yield 78 % (71 mg); m.p. >300 °C.
1H NMR (400 MHz, CF3CO2D): δ = 9.19 (d, J = 8.0 Hz, 4 H), 8.52 (s,
4 H), 7.19 (t, J = 8.0 Hz, 2 H), 7.58 (m, 4 H), 7.13 (m, 4 H) ppm. IR
259 °C (ref.[21] 276.8–277.4 °C). H NMR (400 MHz, CDCl3): δ = 9.59
1
(KBr): ν = 3428, 2338, 1677, 1406, 1359, 1327, 1298, 1207, 1178,
˜
(dd, J = 7.7, 0.9 Hz, 2 H), 8.39 (dd, J = 6.5, 3.4 Hz, 2 H), 8.28 (dd, J =
7.7, 0.9 Hz, 2 H), 8.10 (t, J = 7.7 Hz, 2 H), 8.03 (s, 2 H), 7.90 (dd, J =
6.5, 3.4 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 143.5, 142.6,
131.6, 130.1, 129.7, 129.7, 129.4, 127.4, 127.0, 126.3, 124 ppm. IR
1132, 1094, 1022, 897, 869, 805, 774, 721 cm–1. The HRMS data
could not be obtained owing to the insoluble nature of the com-
pound.
(KBr): ν = 3049, 2923, 1624, 1480, 1422, 1359, 1334, 1314, 1292,
˜
6,7,15,16-Tetramethylquinoxalino[2′,3′:9,10]phenanthro[4,5-
abc]phenazine (3bc): Yellow solid; yield 91 % (80 mg); m.p. >300 °C
1174, 1094, 1063, 830, 763, 713, 630, 587, 426 cm–1. HRMS: calcd.
for C22H12N2 [M + H]+ 305.1073; found 305.1088.
1
(ref.[22] >420 °C). H NMR (400 MHz, CDCl3): δ = 9.91 (d, J = 8.0 Hz,
4 H), 8.54 (t, J = 8.0 Hz, 2 H), 8.50 (s, 4 H), 2.78 (s, 12 H) ppm. 13C
NMR (101 MHz, CDCl3): δ = 149.6, 137.6, 137.0, 131.0, 130.6, 128.1,
Large-Scale Synthesis: The suggested loading of the reactants is
less than one third of the jar volume (25 mL ZrO2 jar). Compound
3aa was also synthesized from pyrene-4,5-dione (1.2 g), o-phenyl-
enediamine (552 mg), and PTSA (96 mg), yield 1.5 g (94 %).
125.2, 124.6, 21.5 ppm. IR (KBr): ν = 2976, 2915, 1621, 1474, 1449,
˜
1397, 1353, 1338, 1215, 1112, 1027, 998, 066, 894, 815, 723,
445 cm–1. HRMS: calcd. for C32H22N4 [M + H]+ 463.1917; found
463.1916.
Benzo[i]phenanthro[4,5-abc]phenazine (3ab):[16] Yellow solid;
1
yield 95 % (72 mg); m.p. >300 °C. H NMR (400 MHz, CF3CO2D): δ =
9.62 (d, J = 7.6 Hz, 2 H), 9.25 (d, J = 3.2 Hz, 2 H), 8.73 (d, J = 7.7 Hz,
2 H), 8.52 (dd, J = 6.3, 3.1 Hz, 2 H), 8.48 (t, J = 7.7 Hz, 2 H), 8.30 (d,
J = 2.3 Hz, 2 H), 8.17 (dd, J = 6.5, 2.9 Hz, 2 H) ppm. 13C NMR
2,7-Di-tert-butylphenanthro[4,5-abc]phenazine (3ca): Yellow
solid; yield 95 % (57 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3):
δ = 9.69 (d, J = 4.0 Hz, 2 H), 8.44 (q, J = 4.0 Hz, 2 H), 8.28 (d, J =
1
(101 MHz, CF3CO2H): δ = 142.0, 138.1, 136.4, 134.2, 133.1, 132.5, 4.0 Hz, 2 H), 8.00 (s, 2 H), 7.89 (q, J = 4.0 Hz, 2 H), 1.67 (s, 18 H)
130.2, 130.1, 129.8, 127.5, 127.3, 125.4, 124.1 ppm. IR (KBr): ν = 3049, ppm. 13C NMR (101 MHz, CDCl3): δ = 149.9, 144.1, 131.4, 129.8,
˜
2917, 1855, 1624, 1421, 1358, 1294, 1262, 1176, 1098, 874, 829, 737,
129.7, 129.2, 127.5, 126.0, 124.5, 121.7, 35.7, 32.1 ppm. IR (KBr): ν =
˜
716, 486 cm–1. HRMS: calcd. for C26H14N2 [M + H]+ 355.1230; found 2961, 2885, 2867, 2333, 1815, 1759, 1612, 1625, 1610, 1477, 1438,
355.1241.
1364, 1353, 1346, 1328, 1259, 1201, 1169, 1112, 1033, 972, 948, 912,
1288 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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887, 803, 760, 723, 582 cm–1. HRMS: calcd. for C30H28N2 [M + H]+
417.2325; found 417.2355.
2,11-Di-tert-butyl-6,7,15,16-tetramethylquinoxalino[2′,3′:9,10]-
phenanthro[4,5-abc]phenazine (3dc): Orange solid; yield 93 %
1
(71 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3): δ = 9.91 (s, 4 H),
2,7-Di-tert-butylbenzo[i]phenanthro[4,5-abc]phenazine (3cb):
Yellow solid; yield 93 % (63 mg); m.p. >300 °C. 1H NMR (400 MHz,
CDCl3): δ = 9.70 (d, J = 4.0 Hz, 2 H), 9.03 (s, 2 H) 8.28 (d, J = 4.0 Hz,
2 H), 8.24 (m, 2 H), 8.00 (s, 2 H), 7.63 (m, 2 H), 1.69 (s, 18 H) ppm.
13C NMR (101 MHz, CDCl3): δ = 150.1, 145.3, 139.1, 134.2, 121.5,
129.3, 128.8, 127.7, 127.4, 126.7, 126.6, 124.7, 122.3, 35.7, 32.1 ppm.
8.52 (s, 4 H), 2.79 (s, 12 H), 1.72 (s, 18 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 154.9, 149.4, 138.0, 136.5, 128.7, 126.4, 124.6, 124.4, 36.7,
31.3, 21.4 ppm. IR (KBr): ν = 2965, 2912, 2867, 2730, 2558, 2347,
˜
1845, 1823, 1677, 1610, 1477, 1400, 1324, 1302, 1280, 1226, 1185,
1136, 1025, 1001, 899, 886, 865, 784, 732, 562 cm–1. HRMS: calcd.
for C40H38N4 [M + H]+ 575.3169; found 575.3190.
IR (KBr): ν = 3051, 2866, 2743, 2713, 2689, 2668, 2485, 2333, 2324,
˜
Dipyrido[3,2-a:2′,3′-c]phenazine (3ea): Orange solid; yield 94 %
(63 mg); m.p. 248–250 °C (ref.[24] 246–247 °C). 1H NMR (400 MHz,
CDCl3): δ = 9.67 (dd, J = 8.1, 1.6 Hz, 2 H), 9.29 (dd, J = 4.4, 1.5 Hz,
2 H), 8.38 (dd, J = 6.5, 3.4 Hz, 2 H), 7.95 (dd, J = 6.5, 3.4 Hz, 2 H),
7.82 (dd, J = 8.1, 4.4 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
152.8, 148.6, 142.7, 141.4, 134.0, 130.9, 129.8, 127.8, 124.4 ppm.
HRMS: calcd. for C14H16N2O3 [M + H]+ 283.0978; found 283.1003.
Benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine (3eb):[25] Orange solid;
yield 92 % (72 mg); m.p. 272–274 °C. 1H NMR (400 MHz, CDCl3): δ =
9.60 (d, J = 7.8 Hz, 2 H), 9.24 (d, J = 3.5 Hz, 2 H), 8.89 (s, 2 H), 8.18
(dd, J = 6.3, 2.9 Hz, 2 H), 7.78 (dd, J = 7.9, 4.4 Hz, 2 H), 7.62 (dd, J =
6.5, 2.9 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 152.7, 148.5,
142.0, 138.8, 134.6, 134.2, 128.7, 128.0, 127.9, 127.3, 124.5 ppm.
HRMS: calcd. for C22H12N4 [M + H]+ 333.1135; found 333.1162.
1625, 1612, 1552, 1480, 1474, 1436, 1390, 1365, 1344, 1283, 1257,
1236, 1201, 1161, 1109, 1098, 975, 948, 890, 803, 739, 723, 601,
616, 578 cm–1. HRMS: calcd. for C34H30N2 [M + H]+ 467.2482; found
467.2509.
2,7-Di-tert-butyl-11,12-dimethylphenanthro[4,5-abc]phenazine
(3cc): Yellow solid; yield 93 % (60 mg); m.p. >300 °C. 1H NMR
(400 MHz, CDCl3): δ = 9.64 (d, J = 4.0 Hz, 2 H), 8.25 (d, J = 4.0 Hz,
2 H), 8.17 (s, 2 H), 7.99 (s, 2 H), 2.62 (s, 6 H), 1.66 (s, 18 H) ppm. 13C
NMR (101 MHz, CDCl3): δ = 149.7, 143.2, 141.5, 140.6, 131.3, 129.5,
128.5, 127.4, 125.6, 124.3, 121.3, 35.7, 32.1, 20.7 ppm. IR (KBr): ν =
˜
2963, 2868, 2331, 1625, 1612, 1509, 1479, 1444, 1363, 1346, 1327,
1262, 1242, 1225, 1209, 1161, 1123, 1057, 1033, 1000, 964, 887, 866,
804, 724, 624, 601, 577 cm–1. HRMS: calcd. for C34H30N2 [M + H]+
445.2638; found 445.2699.
11,12-Dimethyldipyrido[3,2-a:2′,3′-c]phenazine (3ec): White
2,7-Di-tert-butylphenanthro[4,5-abc]phenazine-11-carboxylic
Acid (3cd): Yellow solid; yield 90 % (61 mg); m.p. >300 °C. H NMR
(400 MHz, CDCl3): δ = 9.63 (s, 1 H), 9.53 (s, 1 H), 9.42 (s, 1 H), 8.79
(d, J = 8.0 Hz, 1 H), 8.72 (d, J = 8.0 Hz, 1 H), 8.59 (s, 1 H), 8.53 (s, 1
H), 8.15 (m, 2 H), 1.66 (s, 9 H), 1.62 (s, 9 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 152.5, 152.3, 145.3, 141.3, 138.1, 135.6, 134.1, 133.0,
132.8, 132.3, 132.2, 131.0, 130.9, 128.7, 128.2, 125.9, 124.9, 124.6,
1
solid; yield 95 % (70 mg); m.p. 183–185 °C (ref.[26] 183 °C). H NMR
1
(400 MHz, CDCl3): δ = 9.59 (dd, J = 8.1, 1.4 Hz, 2 H), 9.25 (dd, J =
4.3, 1.4 Hz, 2 H), 8.03 (s, 2 H), 7.78 (dd, J = 8.1, 4.4 Hz, 2 H), 2.58 (s,
6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 152.3, 148.3, 141.9, 141.7,
140.4, 133.6, 128.3, 127.9, 124.1, 20.8 ppm. HRMS: calcd. for
C
20H14N4 [M + H]+ 311.1291; found 311.1318.
124.4, 124.2, 124.0, 36.0, 31.7, 31.5 ppm. IR (KBr): ν = 2661, 2551,
Dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylic Acid (3ed):[27]
˜
1845, 1690, 1616, 1486, 1442, 1363, 1344, 1302, 1283, 1261, 1226,
White solid; yield 91 % (70 mg); m.p. >300 °C. 1H NMR (400 MHz,
1166, 978, 887, 843, 795, 767, 722, 554 cm–1. HRMS: calcd. for CDCl3): δ = 10.12 (t, J = 7.2 Hz, 2 H), 9.35–9.31 (m, 3 H), 8.69–8.67
C
31H28N2O2 [M + H]+ 461.2224; found 461.2249.
(m, 1 H), 8.61 (d, J = 8.9 Hz, 1 H), 8.35 (td, J = 8.1, 5.2 Hz, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 170.3, 148.3, 147.7, 144.5, 141.6,
139.8, 139.3, 139.2, 139.1, 139.0, 138.9, 133.5, 131.2, 131.0, 130.0,
129.0, 128.9, 126.8, 126.8 ppm. HRMS: calcd. for C19H10N4O2 [M +
H]+ 327.0877; found 327.0893.
2,7-Di-tert-butyl-11,12-dichlorophenanthro[4,5-abc]phenazine
(3cf): Yellow solid; yield 92 % (65 mg); m.p. >300 °C. 1H NMR
(400 MHz, CDCl3): δ = 9.59 (d, J = 4.0 Hz, 2 H), 8.53 (s, 2 H), 8.31 (d,
J = 4.0 Hz, 2 H), 8.01 (s, 2 H), 1.67 (s, 18 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 152.5, 142.4, 140.6, 134.7, 132.4, 131.9, 128.5, 125.9,
11,12-Dibromodipyrido[3,2-a:2′,3′-c]phenazine (3ee):[28] White
1
solid; yield 96 % (100 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3):
125.2, 124.1, 122.7, 36.0, 31.5 ppm. IR (KBr): ν = 2958, 2884, 2866,
˜
δ = 10.04 (d, J = 7.5 Hz, 2 H), 9.32 (d, J = 4.0 Hz, 2 H), 8.83 (s, 2 H),
8.32 (dd, J = 8.2, 5.1 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
148.9, 142.4, 140.0, 139.9, 139.6, 133.8, 131.1, 129.9, 127.7 ppm.
HRMS: calcd. for C18H8Br2N4 [M + H]+ 440.9169; found 440.9193.
1906, 1820, 1810, 1799, 1787, 1759, 1752, 1729, 1610, 1593 1473,
1449, 1406, 1383, 1364, 1330, 1287, 1240, 1219, 1171, 1127, 1111,
1103, 986, 888, 866, 798, 722, 528 cm–1. HRMS: calcd. for C34H30N2
[M + H]+ 485.1546; found 485.1526.
11,11′-Bidipyrido[3,2-a:2′,3′-c]phenazine (3eg):[29] Pale yellow
solid; yield 88 % (58 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3):
2,11-Di-tert-butylquinoxalino[2′,3′:9,10]phenanthro[4,5-abc]-
phenazine (3da):[23] Pale yellow solid; yield 92 % (64 mg); m.p.
1
1
δ = 10.23 (d, J = 7.2 Hz, 4 H), 9.34 (s, 4 H), 9.06 (s, 2 H), 8.79 (d, J =
8.8 Hz, 2 H), 8.72 (d, J = 8.8 Hz, 2 H), 8.38 (s, 4 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 148.7, 148.5, 143.9, 143.7, 143.6, 140.6, 140.4,
139.8, 139.7, 139.6, 139.3, 133.0, 131.4, 130.5, 130.4, 128.7, 128.0,
128.0 ppm. HRMS: calcd. for C36H18N8 [M + H]+ 563.1727; found
563.1722.
>300 °C (ref. >300 °C). H NMR (400 MHz, CDCl3): δ = 9.94 (s, 4 H),
8.77 (m, 4 H), 8.39 (m, 4 H), 1.71 (s, 18 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 155.4, 139.4, 137.2, 136.1, 129.7, 127.1, 125.9, 124.6, 36.7,
31.3 ppm. IR (KBr): ν = 2961, 2861, 1951, 1924, 1822, 1709, 1612,
˜
1533, 1479, 1436, 1405, 1383, 1298, 1261, 1184, 1115, 898, 879, 865,
763, 730, 584 cm–1. HRMS: calcd. for C36H30N4 [M + H]+ 519.2543;
found 519.2570.
Tribenzo[a,c,i]phenazine (3fb): Yellow solid; yield 96 % (76 mg);
m.p. 291–293 °C (ref.[25] m.p. 293–294 °C). 1H NMR (400 MHz, CDCl3):
δ = 9.25 (d, J = 7.9 Hz, 2 H), 9.10 (s, 2 H), 8.51 (d, J = 8.0 Hz, 2 H),
8.25–8.24 (m, 2 H), 7.95 (t, J = 7.1 Hz, 2 H), 7.84–7.77 (m, 4 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 140.2, 136.3, 135.2, 133.8, 131.9,
130.5, 130.3, 129.0, 127.3, 124.5, 124.3, 124.2 ppm. HRMS: calcd. for
2,13-Di-tert-butylbenzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]-
phenanthro[4,5-abc]phenazine (3db):[5a] Orange solid; yield 76 %
1
(63 mg); m.p. >300 °C. H NMR (400 MHz, CDCl3): δ = 9.99 (s, 4 H),
9.38 (s, 4 H), 8.84 (m, 4 H), 7.94 (m, 4 H), 1.75 (s, 18 H) ppm. IR (KBr):
ν = 2961, 1984, 1931, 1797, 1674, 1602, 1519, 1380, 1350, 1305,
˜
C
24H14N2 [M + H]+ 331.1230; found 331.1233.
1277, 1238, 1141, 1111, 1033, 960, 943, 905, 875, 831, 779, 754, 742,
668, 545 cm–1. HRMS: calcd. for C44H34N4 [M + H]+ 619.2856; found 11,12-Dimethyldibenzo[a,c]phenazine (3fc):[30] Pale yellow solid;
619.2877.
yield 96 % (71 mg); m.p. 280–282 °C. 1H NMR (400 MHz, CDCl3): δ =
1289 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2016, 1283–1291
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9.20 (dd, J = 8.2, 0.9 Hz, 2 H), 8.60 (d, J = 8.2 Hz, 2 H), 8.33 (s, 2 H),
7.97–7.93 (m, 2 H), 7.86 (t, J = 7.6 Hz, 2 H), 2.69 (s, 6 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 148.3, 138.1, 135.6, 134.1, 133.2, 129.9,
126.3, 124.3, 124.2, 124.1, 21.1 ppm. HRMS: calcd. for C14H16N2O3
[M + H]+ 309.1386; found 309.1368.
Keywords: Synthetic methods · Mechanochemistry · Solvent-
free synthesis · Fused-ring systems · Nitrogen heterocycles ·
Polycycles
11,12-Dibromodibenzo[a,c]phenazine (3fe):[31] Pale yellow solid;
yield 96 % (101 mg); m.p. 278–280 °C. 1H NMR (400 MHz, CDCl3):
δ = 9.33 (d, J = 7.6 Hz, 2 H), 8.65 (s, 2 H), 8.57 (d, J = 8.0 Hz, 2 H),
7.85 (t, J = 7.4 Hz, 2 H), 7.77 (t, J = 7.3 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 143.6, 141.4, 133.5, 132.6, 131.2, 130.0, 128.4,
126.7, 126.5, 123.3 ppm. HRMS: calcd. for C20H10Br2N2 [M + H]+
436.9283; found 436.9233.
[1] a) M. Watanabe, K.-Y. Chen, Y. J. Chang, T. J. Chow, Acc. Chem. Res. 2013,
46, 1606–1615; b) H. Usta, A. Facchetti, T. J. Marks, Acc. Chem. Res. 2011,
44, 501–510; c) J. E. Anthony, Angew. Chem. Int. Ed. 2008, 47, 452–483;
Angew. Chem. 2008, 120, 460; d) W. Jiang, Y. Li, Z. Wang, Chem. Soc. Rev.
2013, 42, 6113–6127; e) M. Randić, Chem. Rev. 2003, 103, 3449–3606.
[2] Y. Ruiz-Morales, J. Phys. Chem. A 2002, 106, 11283–11308.
[3] W. Yue, S. L. Suraru, D. Bialas, M. Muller, F. Wurthner, Angew. Chem. Int.
Ed. 2014, 53, 6159–6162; Angew. Chem. 2014, 126, 6273.
[4] a) L. Qiu, X. Zhuang, N. Zhao, X. Wang, Z. An, Z. Lan, X. Wan, Chem.
Commun. 2014, 50, 3324–3327; b) A. Mateo-Alonso, N. Kulisic, G. Valenti,
M. Marcaccio, F. Paolucci, M. Prato, Chem. Asian J. 2010, 5, 482–485.
[5] a) N. Kulisic, S. More, A. Mateo-Alonso, Chem. Commun. 2011, 47, 514–
516; b) A. Mateo-Alonso, Chem. Soc. Rev. 2014, 43, 6311–6324.
[6] B. Kohl, F. Rominger, M. Mastalerz, Org. Lett. 2014, 16, 704–707.
[7] a) R. B. N. Baig, R. S. Varma, Chem. Soc. Rev. 2012, 41, 1559–1584; b) S.
Ley, M. O'Brien, R. Denton, Synthesis 2011, 1157–1192.
2,2′,3,3′-Tetraphenyl-6,6′-biquinoxaline (3gg): Pale yellow solid;
yield 96 % (66 mg); m.p. >300 °C (ref.[32] >300 °C). 1H NMR (400 MHz,
CDCl3): δ = 8.62 (s, 2 H), 8.35 (d, J = 8.4 Hz, 2 H), 8.26 (d, J = 8.2 Hz,
2 H), 7.58 (d, J = 6.0 Hz, 4 H), 7.38 (d, J = 6.5 Hz, 10 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 154.4, 153.9, 141.7, 141.4, 141.2, 139.2,
130.2, 130.1, 129.7, 129.2, 128.5, 127.7 ppm. HRMS: calcd. for
C40H26N4 [M + H]+ 563.2230; found 563.2244.
2,3,7,8-Tetraphenylpyrazino[2,3-g]quinoxaline (3gh):[33] Yellow
solid; yield 90 % (50 mg); m.p. 280–282 °C. 1H NMR (400 MHz,
CDCl3): δ = 9.03 (s, 2 H), 7.63 (d, J = 6.7 Hz, 8 H), 7.45–7.38 (m, 12
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 155.6, 140.7, 139.1, 130.3,
129.7, 129.1, 128.6 ppm. HRMS: calcd. for C34H22N4 [M + H]+
487.1917; found 487.1947.
[8] a) A. Stolle, T. Szuppa, S. E. S. Leonhardt, B. Ondruschka, Chem. Soc. Rev.
2011, 40, 2317–2329; b) G.-W. Wang, Chem. Soc. Rev. 2013, 42, 7668–
7700.
[9] a) J. G. Hernández, C. G. Avila-Ortiz, E. Juaristi, in: Comprehensive Organic
Synthesis II (Ed.: P. Knochel), 2nd ed., Elsevier, Amsterdam, The Nether-
lands, 2014, p. 287–314; b) L. Takacs, Chem. Soc. Rev. 2013, 42, 7649–
7659; c) S. L. James, T. Friscic, Chem. Soc. Rev. 2013, 42, 7494–7496; d)
S. L. James, C. J. Adams, C. Bolm, D. Braga, P. Collier, T. Friscic, F. Grepioni,
K. D. M. Harris, G. Hyett, W. Jones, A. Krebs, J. Mack, L. Maini, A. G. Orpen,
I. P. Parkin, W. C. Shearouse, J. W. Steed, D. C. Waddell, Chem. Soc. Rev.
2012, 41, 413–447.
[10] S. Maiti, P. Mal, Synth. Commun. 2014, 44, 3461–3469.
[11] a) P. K. Sahoo, A. Bose, P. Mal, Eur. J. Org. Chem. 2015, 6994–6998; b) T. K.
Achar, P. Mal, J. Org. Chem. 2015, 80, 666–672; c) A. Bose, P. Mal, Tetrahe-
dron Lett. 2014, 55, 2154–2156; d) T. K. Achar, S. Maiti, P. Mal, RSC Adv.
2014, 4, 12834–12839.
Fluorescence Quantum Yield Determination: For fluorescence
quantum yield determination, quinine sulfate[34] was used as the
standard (ΦFl = 0.577 in 0.1
was 350 nm). In a typical measurement, heteroacene stock solution
(20 μL, 2.5 × 10–3
in dichloromethane) was added to solvent
N H2SO4, the irradiation wavelength
M
(2.5 mL). Fluorescence wavelengths from 385 to 650 nm were con-
sidered for the calculation:
[12] C. Giri, P. K. Sahoo, R. Puttreddy, K. Rissanen, P. Mal, Chem. Eur. J. 2015,
21, 6390–6393.
[13] a) L. Carlier, M. Baron, A. Chamayou, G. Couarraze, Tetrahedron Lett. 2011,
52, 4686–4689; b) S. Paul, B. Basu, Tetrahedron Lett. 2011, 52, 6597–6602.
[14] J. Hu, D. Zhang, F. W. Harris, J. Org. Chem. 2005, 70, 707–708.
[15] A. Mateo-Alonso, N. Kulisic, G. Valenti, M. Marcaccio, F. Paolucci, M. Prato,
Chem. Asian J. 2010, 5, 482–485.
[16] A. Mateo-Alonso, C. Ehli, K. H. Chen, D. M. Guldi, M. Prato, J. Phys. Chem.
A 2007, 111, 12669–12673.
[17] A. Mateo-Alonso, N. Kulisic, G. Valenti, M. Marcaccio, F. Paolucci, M. Prato,
Chem. Asian J. 2010, 5, 482–485.
[18] J. Fleischhauer, S. Zahn, R. Beckert, U.-W. Grummt, E. Birckner, H. Görls,
Chem. Eur. J. 2012, 18, 4549–4557.
[19] Y. Wu, Z. Yin, J. Xiao, Y. Liu, F. Wei, K. J. Tan, C. Kloc, L. Huang, Q. Yan, F.
Hu, H. Zhang, Q. Zhang, ACS Appl. Mater. Interfaces 2012, 4, 1883–1886.
[20] U. H. F. Bunz, Chem. Eur. J. 2009, 15, 6780–6789.
Here, ꢀ = quantum yield, A = absorbance at a given wavelength
(350 nm), n = refractive index, and α = the area under the fluores-
cence spectrum. Indices 1 and 2 designate the sample and stand-
ard, respectively.
X-ray Crystallography: The single-crystal X-ray diffraction data
were collected at room temperature with a Bruker-SMART-APEX II
D8 diffractometer with Mo-Kα (λ = 0.71073 Å) radiation. CCDC
1437948 (for 3ac), 1437949 (for 3ae), 1437950 (for 3ba), and
1437951 (for 3cf) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre.
[21] F. G. Oberender, J. A. Dixon, J. Org. Chem. 1959, 24, 1226–1229.
[22] B. Wex, A. a. O. El-Ballouli, A. Vanvooren, U. Zschieschang, H. Klauk, J. A.
Krause, J. Cornil, B. R. Kaafarani, J. Mol. Struct. 2015, 1093, 144–149.
[23] T. Yamato, M. Fujimoto, A. Miyazawa, K. Matsuo, J. Chem. Soc. Perkin
Trans. 1 1997, 1201–1208.
Supporting Information (see footnote on the first page of this
article): experimental methods, spectroscopic investigations, syn-
thetic procedure, characterization data, and spectra.
[24] F. Ferretti, E. Gallo, F. Ragaini, J. Organomet. Chem. 2014, 771, 59–67.
[25] W. Guo, B. J. Engelman, T. L. Haywood, N. B. Blok, D. S. Beaudoin, S. O.
Obare, Talanta 2011, 87, 276–283.
[26] A. Kleineweischede, J. Mattay, Eur. J. Org. Chem. 2006, 947–957.
[27] A. J. McConnell, M. H. Lim, E. D. Olmon, H. Song, E. E. Dervan, J. K. Barton,
Inorg. Chem. 2012, 51, 12511–12520.
[28] B. Schafer, H. Gorls, M. Presselt, M. Schmitt, J. Popp, W. Henry, J. G. Vos,
S. Rau, Dalton Trans. 2006, 2225–2231.
[29] A. K. Bilakhiya, B. Tyagi, P. Paul, P. Natarajan, Inorg. Chem. 2002, 41, 3830–
3842.
Acknowledgments
The authors are thankful to the Department of Science and
Technology (DST), New Delhi for financial support (grant num-
bers INT/FINLAND/P-06 and SR/S1/IC-59/2010). P. K. S. is thank-
ful to the University Grants Commission (UGC), New Delhi for a
fellowship. The Academy of Finland (grants 263256 and 265328
to K. R.) and the University of Jyvaskyla, Finland are also grate-
fully acknowledged for financial support.
[30] S. M. Baghbanian, Chin. Chem. Lett. 2015, 26, 1113–1116.
Eur. J. Org. Chem. 2016, 1283–1291
www.eurjoc.org
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[31]
[34] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Springer, New York,
2006, p. 27–61.
A. Putta, J. D. Mottishaw, Z. Wang, H. Sun, Cryst. Growth Des. 2014, 14,
350–356.
[32] M. Lian, Q. Li, Y. Zhu, G. Yin, A. Wu, Tetrahedron 2012, 68, 9598–9605.
[33] H. Takeshita, A. Mori, T. Nagao, T. Nagamura, Chem. Lett. 1989, 18, 1719–
1722.
Received: January 4, 2016
Published Online: January 19, 2016
Eur. J. Org. Chem. 2016, 1283–1291
www.eurjoc.org
1291
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim